Author: admin

Study design and target groups

A cross-sectional study was conducted across Egypt’s distinct geographical and socioeconomic regions from January to September 2022. The study targeted adolescents of both genders, aged 10–19 years, who consented to participate. The participants were categorized according to the World Health Organization (WHO) criteria for the stages of adolescence [40], early adolescence (10–13 years), middle adolescence (14–16 years), and late adolescence (17–19 years). The study aimed to assess the nutritional literacy of adolescents across these age groups.

Sample size calculation and selection

The sample size was calculated based on an estimated proportion of 18.1% for adolescents with inadequate total nutrition literacy (TNL) in each adolescence stage. A sample size of 297 provided a two-sided 97% confidence interval with a margin of error of 0.100. The sample size was calculated as follows [41].

Numeric results for Two-Sided confidence intervals for one proportion

Confidence interval formula: exact (Clopper-Pearson)

To ensure representation across the three stages of adolescence and socioeconomic strata, the sample size was increased to 1,050 participants, with 350 adolescents from each age group (early, middle, and late adolescence) [42]. By focusing on adolescents, the study captures a critical period of development during which nutrition literacy can significantly impact both immediate and long-term health outcomes.

Study setting and participant selection

Participants were recruited from households through a multi-stage random sampling approach. Stage one was the selection of governorates to represent the main districts of four Egyptian regions. each governorate represented distinct geographical and dietary regions of Egypt: Cairo (representative of the Greater Cairo region representing Urban/metropolitan region); Fayoum (representative of Upper Egypt representing Agricultural region); Al Dakhlyia (representative of the Delta region) and Marsa Matrouh (representative of a border/frontier governorate). Each region has unique dietary habits and crops, contributing to the study’s focus on the diversity of dietary patterns across Egypt. These governorates were randomly chosen to capture various dietary practices, socioeconomic backgrounds, and cultural influences on nutrition. This selection enhances the study’s relevance to Egypt’s broader context [43, 44]. Cairo is a dense urban setting with high dietary diversity, while Fayoum and Al Dakhlyia represent agricultural areas with traditional dietary practices, and Marsa Matrouh, a frontier region, has limited food access compared to other areas.

For each governorate, both urban and rural areas were targeted for addressing the regional variability in nutrition literacy. By including both urban and rural households in each governorate, this study accounts for these disparities, enhancing the generalizability of the findings. During phase three, participants were stratified by socioeconomic status (SES) using the Economic Research Forum and CAPMAS (Central Agency for Public Mobilization and Statistics) wealth index (low, middle, and high). To minimize selection bias, random sampling was conducted in urban and rural districts within each SES group, with three cities and three local village units chosen per stratum. This structured approach also addresses potential oversampling biases in urbanized areas, ensuring that rural adolescent voices are represented adequately [45]. This selection was designed as part of a broader effort to identify children at high risk for autism, and it adhered to the study’s inclusion and exclusion criteria [46]. Adolescents were randomly selected through a community house-to-house approach.

For each targeted governorate, 45 participants (15 per adolescent stage) were recruited from each social class, resulting in a total of 225 adolescents from each governorate, with the exception of the Cairo governorate, which had 270 participants (90 per each social class, 30 per each adolescent stage).

Inclusion criteria

The study included adolescents aged 10–19 years, classified according to the World Health Organization (WHO) adolescence stages, encompassing early, middle, and late adolescence. Both male and female participants were eligible, provided they had been residing in the selected governorates for at least one year to ensure their dietary habits reflected the local environment. To account for variations in educational background, the study included adolescents actively attending school in public, private, or community-based educational institutions, as well as those who had dropped out of school but had completed at least six years of formal education, ensuring they possessed the necessary literacy skills to engage with the study materials. Additionally, informed parental consent and adolescent assent were mandatory for participation.

Exclusion criteria

Adolescents were excluded from the study if they had diagnosed cognitive impairments or severe learning disabilities that could hinder their ability to complete the nutrition literacy assessment. Those who had not completed at least six years of formal education were also excluded, as they might lack the foundational literacy skills required for the questionnaire To minimize confounding factors, adolescents with chronic medical conditions affecting nutrition intake, such as diagnosed eating disorders or metabolic disorders, were excluded unless their condition was a specific focus of the study. Additionally, non-Egyptian adolescents or those who had moved to Egypt within the past year were not included, as their dietary habits and environmental influences might not align with the local context. To prevent potential clustering biases within families, only one adolescent per household was selected for participation.

Data collection instruments and procedures

Questionnaire administration

A self-administered questionnaire was utilized to gather data from the adolescent participants. This questionnaire was filled out under the guidance of the research team to ensure clarity and accuracy. The questionnaire was adapted from a previously validated tool, originally designed and published by Hoteit and colleagues [47], ensuring its relevance to the adolescent population in the context of nutrition literacy (NL) assessment. A pilot study involving 10% of the participants was conducted before the main study to enhance clarity, minimize ambiguity, and address potential sources of measurement error.

The questionnaire was divided into two major sections:

Demographic and socioeconomic information

This section focused on collecting essential background information on the enrolled adolescents. The demographic variables collected included the participants’ age, gender, educational level, and details on their primary caregiver (i.e., who was primarily responsible for their daily care). Additionally, the study gathered data on the education levels of both parents, as parental education often influences the nutritional habits and literacy of children. Household Crowding Index: Calculated as the number of co-residents (excluding newborns) divided by the number of rooms (excluding kitchens and bathrooms [48,49,50].

Parents provided self-reported anthropometric data (weight and height) to calculate Body Mass Index (BMI), facilitating assessment of nutritional status in line with WHO’s BMI-for-age guidelines. Participants were instructed to provide recent height and weight measurements to reduce potential reporting biases, particularly in anthropometric data. However, the reliance on self-reported anthropometrics remains a limitation, as it introduces the possibility of data inaccuracy, an issue common in large-scale, self-administered surveys Participants also reported on their intake of vitamins and minerals, providing insight into their dietary supplementation habits.

Vitamins assessment

Assessing adolescents’ consumption of dietary supplements focused on participants’ report on vitamins D, C, A, B12, and folic acid intake. Assessment of these particular vitamins was crucial due to the essential roles these micronutrients play during this critical developmental stage. Adolescence is marked by rapid growth and physiological changes, increasing the demand for nutrients that support bone development, immune function, cognitive maturation, and overall health.​ Monitoring supplement intake in this demographic helps identify nutritional gaps and informs interventions aimed at promoting balanced diets rich in essential vitamins.

Vitamin D

is vital for calcium absorption and bone mineralization, processes that are foundational during the adolescent growth spurt. Adequate vitamin D levels are necessary to achieve optimal bone density, reducing the risk of osteoporosis and fractures later in life [51].​.

Vitamin C

serves as a potent antioxidant and is essential for collagen synthesis, which is integral to the structural integrity of skin, blood vessels, and connective tissues. It also enhances immune defense mechanisms, aiding in the prevention and recovery from infections [52, 53].​.

Vitamin A

is crucial for vision, immune competence, and cellular differentiation. During adolescence, sufficient vitamin A intake supports the development of epithelial tissues and bolsters the body’s ability to combat pathogens [54].

Vitamin B12

is indispensable for neurological function and the formation of red blood cells. Its role in DNA synthesis and myelination of nerve fibers is particularly pertinent during adolescence, a period characterized by significant cognitive and physical development [55].​.

Folic acid (vitamin B9)

is essential for DNA synthesis and repair, supporting rapid cell division and growth. Adequate folic acid intake is vital during adolescence to prevent megaloblastic anemia and to support neural development [56].

Minerals assessment

Understanding which supplements adolescents consume provides insights into existing nutrient gaps and overall dietary patterns. Dietary supplements, such as multivitamin/mineral products, have been shown to help fill nutrient gaps and improve micronutrient sufficiency among children and adolescents. However, there is a concern about the over-reliance on supplements as substitutes for whole foods, which can lead to lower overall energy intake and lack of consumption of other critical nutrients found in whole foods [57, 58]. The current study focused on participants’ report on consumption of dietary supplements, specifically calcium, magnesium, iron, and zinc, that is grounded in their critical role in growth, development, and overall health during this life stage [59]. Adolescence is a period of rapid skeletal growth and bone mineralization, making calcium and magnesium essential for maintaining strong bones and preventing future conditions like osteoporosis and fractures. Since bone mass peaks during adolescence, ensuring adequate intake of these minerals is crucial for long-term musculoskeletal health [60, 61].

Beyond skeletal development, iron and zinc are fundamental for cognitive function, immune health, and metabolic processes. Iron deficiency is a leading cause of anemia among adolescents, particularly in females due to increased iron loss from menstruation, which can lead to fatigue, decreased concentration, and poor academic performance [62]. Similarly, zinc plays a key role in immune function, wound healing, and enzymatic reactions, helping adolescents maintain overall health and fight infections during a stage of high physiological demand [63].

In this study, data on vitamin and mineral intake reflect self-reported use of dietary supplements only, specifically including calcium, magnesium, iron, zinc, and multivitamin preparations. These data do not include intake from food sources. Dietary intake of vitamins and minerals from regular meals was assessed as part of a broader project; however, those findings are presented in a separate manuscript.

Nutrition literacy and food literacy assessment

The second part of the questionnaire measured the nutrition literacy (NL) of the adolescents and the food literacy of their parents. Nutrition literacy refers to the ability to obtain, process, and understand basic nutrition information needed to make appropriate health decisions.

To assess NL, the Adolescent Nutrition Literacy Scale (ANLS) developed by Bari [64], was utilized. This comprehensive tool consists of 22 questions, categorized into three distinct components:

• Functional Nutrition Literacy (FNL): This component, composed of 7 questionsassessing basic nutritional information comprehension. It evaluated the adolescents’ ability to comprehend and use basic nutritional information, such as their understanding of nutrition-related scientific terms, dietary guidelines, and the recommendations provided by public health professionals. For instance, it included questions assessing participants’ familiarity with international dietary guidelines, such as those from the World Health Organization (WHO) regarding fruit and vegetable intake. The scoring range for FNL is 7–35, with a cut off score of ≥ 21 indicating adequate functional literacy.

• Interactive Nutrition Literacy (INL): The 6 questionsin this component measured the adolescents’ skills in seeking out, discussing, and applying nutrition-related informationwithin social contexts, including communication with peers, family members, and health professionals. The ability to engage with nutrition topics and translate this knowledge into practical actions, such as modifying dietary habits based on newly acquired information, was a key aspect of this component. The score for INL ranges from 6 to 30, with a cut off score of ≥ 18 considered adequate.

• Critical Nutrition Literacy (CNL): The9 questionsin this section focused on the adolescents’ ability to critically assess nutrition information and influenceothers’ dietary practices. It assessed participants’ engagement in activities that promote healthy eating, support for policies that improve dietary habits, and their ability to evaluate the credibility of nutrition-related information, particularly from social media and other sources. The score range for CNL is 9–45, with a cut off score of ≥ 27 indicative of sufficient critical literacy.

Total nutrition literacy (TNL)

was calculated as the sum of the three components (FNL, INL, CNL), yielding a total possible score between 22 and 110. A cut off score of ≥ 66 reflected adequate overall nutrition literacy. This metric provided a comprehensive view of the adolescents’ ability to understand, interact with, and critically evaluate nutrition information.

To assess parental food literacy, the validated Short Food Literacy Questionnaire (SFLQ) developed by Gréa Krause et al. [65] was used. The parental food literacy questionnaire was composed of 12 questions, divided across three dimensions similar to those assessed in the adolescent scale but with fewer questions per category: Functional food literacy (6 questions); Interactive food literacy (2 questions); Critical food literacy (4 questions).

The parental food literacy score ranged from 7 to 52, with a cut off score of ≥ 36 indicating adequate food literacy. This allowed for comparison between the literacy levels of parents and their children, providing a deeper understanding of family dynamics regarding nutrition knowledge and behaviors.

Nutritional and growth status assessment

In addition to the self-reported data of the parents, a physical assessment of nutritional status was conducted. By conducting in-person measurements, this study enhances data reliability and consistency across rural and urban participants. Additionally, anthropometric data allows for exploring relationships between growth status and nutrition literacy, which could reveal developmental implications of inadequate nutrition literacy during adolescence. Anthropometric measurements of weight and height were taken using standardized equipment and techniques. Weight was measured with a Seca Scale Balance, while height was recorded using a Holtain portable anthropometer. These measurements were critical for evaluating the growth status of the adolescents, as weight and height are primary indicators of nutritional health. The BMI was calculated as weight (in kilograms) divided by height (in meters) squared based on the WHO growth standards with the help of the Anthro-Program of PC [66]. The body mass index (BMI) was evaluated as follows: underweight if BMI is less than 18.5, normal/healthy weight if BMI is 18.5 to 24.9, overweight is BMI is 25.0 to 29.9, and obese if BMI is 30.0 or higher [67]. The BMI classification provided an additional layer of insight into the participants’ nutritional health, correlating with their dietary habits and nutrition literacy levels.

Measures to ensure validity and reliability of tools used for NL and FL assessment

Both ANLS that is developed by Bari [64] and SFLQ that is developed by Gréa Krause et al. [65] have been translated, culturally adapted and utilized in Arabic-speaking contexts. They have been adapted in a study to assess the nutrition literacy of adolescents across countries including Lebanon, Bahrain, Egypt, Jordan, Kuwait, Morocco, Palestine, Qatar, Saudi Arabia, and the United Arab Emirates [68]. The study involved 5,401 adolescent-parent dyads and found that 28% of adolescents had poor nutrition literacy. However, the study did not detail the process of translating or validating the ANLS and SFLQ for each specific Arabic-speaking context and it did not provide specific psychometric properties of the Arabic-translated tools.

We have conducted a multistep process to mitigate this for ensuring the tools appropriateness for our target population. Initially, a pilot test was conducted before large-scale implementation to ensure the clarity and appropriateness of the translated Arabic ANLS and SFLQ tools. This step involved administer of the Arabic versions of the tools for 10% of different participants as a pilot sample (n = 105) to assess their usability and ensure that participants could complete the questionnaire without difficulty. Subsequently, to assess internal consistency, the study employed Cronbach’s alpha [69]. with a larger sample of 330 participants, achieving high values of Cronbach’s alpha (0.89 for ANLS and 0.86 for SFLQ, ≥ 0.8) that indicated strong reliability [70]. To assess the stability of responses over time, a subset of 105 participants completes the Arabic SFLQ twice, with a two-week interval (test-retest reliability). The Intraclass Correlation Coefficient (ICC) was calculated to measure consistency, achieving ICC of 94% and 92% respectively indicating excellent reliability (ICC ≥ 0.75) [71]. This comprehensive approach ensured that the Arabic ANLS and SFLQ are scientifically sound and culturally relevant tool for assessing nutrition literacy among Arabic-speaking adolescents.

Statistical analysis

Data were analyzed using the Statistical Package for Social Sciences (SPSS), version 26. Various statistical techniques were employed to summarize and analyze the collected data: Categorical variables (e.g., gender, social class, nutritional literacy categories) were summarized as numbers and percentages. Continuous variables (e.g., BMI, literacy scores) were presented as means and standard deviations.

Statistical significance was determined using: Pearson’s Chi-square test (χ²) and Fisher’s exact test to assess associations between categorical variables. Z-tests were applied for comparisons of proportions.For comparisons of means between groups, the t-test and ANOVA were utilized. Crude Odds Ratio (COR) with 95% confidence intervals (CI) were calculated to examine associations between adolescence stages and nutritional literacy. Logistic regression analysis was conducted to identify significant predictors of adequate TNL among the adolescents.A p-value < 0.05 was considered statistically significant, indicating a meaningful association or difference, while a p–value < 0.01 was considered highly important, highlighting particularly strong associations or differences.

Introduction

Obesity has emerged as a global epidemic and has a significant impact on human health and socio-economic outcomes. According to the latest data, the total number of children with obesity, adolescents with obesity and adults with obesity worldwide has exceeded 1 billion. In 2022, 159 million children with obese and 879 million adults with obese worldwide. Obesity is prevalent not only in developed countries, but also rapidly spreading in low- and middle-income countries. More than 750 million adolescents (5–19 years) worldwide are expected to be overweight or obese by 2035.^1,2 The negative health impacts of obesity are multifaceted. Obesity is an important risk factor for non-communicable diseases such as cardiovascular disease, type 2 diabetes, and certain cancers.³ In addition, obesity is associated with multiple psychosocial problems, such as impaired self-esteem, social discrimination, and decreased quality of life. Obesity in childhood and adolescence not only impacts their immediate health, but also increases the risk of chronic diseases in adulthood.⁴ Obesity also places a huge burden on the global economy, and the global cost of overweight and obesity is expected to reach $3 trillion per year by 2030.⁵

Metabolic and bariatric surgery (MBS) has a crucial role in the treatment of severe obesity. MBS is one of the most effective methods to achieve sustained long-term weight loss, especially for those patients who fail to achieve successful weight loss with diet, exercise, and medical therapy. Surgery promotes a significant decrease in body weight by altering the anatomy and function of the gastrointestinal tract, reducing the intake and absorption of food, while affecting the appetite regulation mechanisms of patients.⁶ MBS is not only effective in reducing body weight, but also significantly improves or resolves a variety of metabolic diseases associated with obesity, such as type 2 diabetes, hypertension, hyperlipidemia and obstructive sleep apnea.⁷ The improvement of these diseases not only improves the quality of life of patients, but also reduces long-term medical costs and the risk of death.⁷ MBS addresses not only the physical aspects of obesity but also significantly impacts mental health and overall patient experience. Obesity is often associated with psychological challenges such as depression, anxiety, and low self-esteem, which can be exacerbated by social stigma and discrimination. These psychological factors play a crucial role in the success of MBS and the long-term outcome of patients. A comprehensive patient-centered approach that integrates psychological support and addresses patient experience is essential to optimize surgical outcomes and improve quality of life. Preoperative psychological assessment is essential to identify patients who may be at risk for adverse mental health outcomes. This includes screening obese people for prevalent depression, anxiety, and eating disorders. Providing psychological support and counseling before surgery can help patients develop coping strategies and improve mental health, thereby enhancing the preparation of surgery and postoperative recovery. Following surgery, patients’ mental health should continue to be prioritized. Many patients experience significant lifestyle changes following MBS, which can lead to emotional and psychological challenges.¹ Regular follow-up with mental health professionals can help address these issues and provide ongoing support. In addition, support groups and peer coaching programs have been shown to be beneficial in improving patient experience and long-term adherence to lifestyle changes. Patient education and participation in decision-making processes are critical components of a patient-centered approach. Patients should be fully informed about the surgical procedure, potential risks, and expected outcomes. Involving patients in the development of their nutrition and lifestyle programs can enhance their sense of control and improve compliance with postoperative recommendations. However, it is important to note that MBS, like any surgical intervention, carries certain risks and potential complications. These may include surgical site infections, bleeding, thromboembolic events, and anesthesia-related risks. Additionally, some patients may experience long-term complications such as nutritional deficiencies, dumping syndrome, or gastrointestinal reflux.⁸ Although surgery carries certain risks and complications, its combined benefits in the treatment of severe obesity far outweigh these potential risks, providing patients with a comprehensive and lasting solution.⁸ However, it is important to note that MBS, like any surgical intervention, carries certain risks and potential complications.

Perioperative nutritional management plays a crucial role in MBS. First, in the preoperative period, the main goal of nutritional management is to improve the nutritional status of patients and reduce the degree of malnutrition, thereby improving the patient tolerance to surgical trauma and reducing the incidence of postoperative complications.⁹ To achieve this, specific interventions are essential. Preoperative dietary modifications should prioritize low-fat and low-energy diets, which can help reduce overall caloric intake while ensuring adequate nutrient intake. Additionally, multivitamin and mineral supplements, including vitamin D, iron, and folic acid, should be administered to address common micronutrient deficiencies observed in obese patients. These supplements are crucial for optimizing nutritional status and preventing postoperative complications such as anemia and metabolic bone disease. Reasonable nutritional therapy, such as low-fat, low-energy diet and multivitamin and mineral supplementation, can effectively reduce the patient’s weight, reduce liver volume, improve surgical field exposure, and increase the success rate of surgery.^10,11 In addition, preoperative nutritional management can also help patients adapt to the feeding pattern in the postoperative volume-restricted state and reduce the loss of lean body tissue and bone mass after surgery. During the intraoperative period, perioperative nutritional management helps to maintain blood glucose levels and fluid balance in patients and reduce the damage of surgical stress to the body. After surgery, nutritional management focuses on promoting rapid recovery of patients and preventing the occurrence of malnutrition.¹² A low-energy, high-protein diet should be given early after surgery to maintain muscle mass and promote wound healing. A high-protein diet typically refers to a diet that provides at least 1.2 to 1.5 grams of protein per kilogram of body weight per day, which is higher than the general dietary recommendation for the average adult. For example, a patient weighing 70 kg should aim to consume between 84 and 105 grams of protein daily. This recommendation is based on evidence that higher protein intake supports muscle preservation and overall metabolic health during the recovery phase.¹² Diverse Protein Sources To achieve the recommended protein intake, patients should be encouraged to consume a variety of protein-rich foods. These can include: Animal Proteins: Lean meats such as chicken breast (31 grams of protein per 100 grams), turkey (28 grams of protein per 100 grams), and fish-like salmon (20 grams of protein per 100 grams) and cod (17 grams of protein per 100 grams). Dairy products such as Greek yogurt (10 grams of protein per 100 grams) and cottage cheese (11 grams of protein per 100 grams) are also excellent sources. Plant-Based Proteins: Legumes like lentils (9 grams of protein per 100 grams) and chickpeas (8 grams of protein per 100 grams), as well as tofu (8 grams of protein per 100 grams), provide essential amino acids and support a balanced diet for patients who prefer or require vegetarian options. These foods not only provide essential amino acids but also help in maintaining satiety and supporting overall health. It is important to note that protein sources should be easily digestible, especially in the early postoperative period when patients may experience gastrointestinal sensitivity. In addition to macronutrient management, postoperative micronutrient supplementation is crucial to prevent deficiencies. Patients should receive regular supplementation with key vitamins and minerals, including vitamin D, vitamin B12, folic acid, and iron. Supplementation should be tailored based on individual nutritional assessments and laboratory tests to ensure adequate levels of these micronutrients. Nutritional therapy should be started as early as possible in patients with malnutrition or nutritional risk, and enteral or parenteral nutrition support should be used if necessary.¹³ In addition, long-term nutritional monitoring and supplementation are required after surgery to prevent and correct micronutrient deficiencies and maintain the long-term nutritional status of patients. Specifically, it is recommended to perform comprehensive nutritional assessments every 3 months in the first year after surgery, including blood tests for micronutrients such as iron, zinc, copper, vitamin B1, B9, B12, D, A, and E, as well as bone mineral density testing and liver and kidney function indicators. In the second year, monitoring can be adjusted to biannual, and then at least once a year focusing on key indicators. For patients at high risk of nutritional deficiencies, such as those with severe preoperative malnutrition or postoperative complications, more frequent monitoring and personalized supplementation plans are essential. In conclusion, perioperative nutritional management runs through the whole process of MBS and is of great significance to improve the surgical effect and promote the postoperative recovery of patients. To maintain good weight loss, scientific nutritional management is still required during the perioperative period.¹⁴ However, perioperative nutritional management also faces several challenges. These include patient compliance with dietary and supplement regimens, variability in nutritional needs based on individual factors such as surgical type and pre-existing conditions, and the necessity for long-term monitoring to prevent and address nutritional deficiencies. Addressing these challenges is essential to optimize patient outcomes. The aim of this literature review is to present the latest advancements in perioperative nutritional management in MBS and provide insights for optimizing the nutrition of these patients.

Prevalence and Influencing Factors of Preoperative Malnutrition

Preoperative malnutrition is prevalent in patients with MBS and has a high incidence. Studies have shown that obese patients have prevalent deficiencies of multiple micronutrients before surgery, including vitamin D, iron, folic acid, vitamin B12, vitamin A, thiamine, and zinc. Preoperative vitamin D deficiency may be present in up to 76%, iron deficiency in 6% to 50.5%, folic acid deficiency in 0% to 56%, low MCV in 19% to 47.9%, and anemia in 15.8% to 19.6%.^15–19 This malnourished condition not only impacts the quality of life of patients, but may also increase the risk of postoperative complications, such as anemia, neurological disorders, and metabolic bone disease.^20–22 To address these deficiencies before surgery, specific interventions are recommended based on the type and severity of the deficiency. For patients with vitamin D deficiency, oral vitamin D supplements are typically prescribed, with the daily dose adjusted according to serum 25(OH)D levels. The goal is to maintain serum 25(OH)D levels above 30 ng/mL. For iron deficiency, oral iron supplements are usually the first-line treatment, although intravenous iron may be considered in cases of severe deficiency or poor gastrointestinal absorption. Regular monitoring of serum ferritin and hemoglobin levels is essential to assess the effectiveness of the supplementation. In cases of severe anemia, additional interventions such as intravenous iron or even transfusions may be necessary (Table 1).

Table 1 Common Micronutrient Deficiencies and Recommended Supplementation Strategies in Metabolic and Bariatric Surgery

The occurrence of preoperative malnutrition is influenced by multiple factors. Obese patients usually have long-term imbalance in dietary intake, and their diet is often dominated by foods with high calorie and low nutritional quality, resulting in insufficient intake of micronutrients.²³ Second, obesity itself decreases the bioavailability of certain nutrients, for example, vitamin D is easily taken up by adipose tissue due to its lipid solubility, thereby reducing its concentration in blood.²⁴ In addition, obesity-related chronic inflammation can also affect nutrient absorption and utilization, such as iron absorption and utilization may be negatively affected by chronic inflammation. Female patients have a higher risk of preoperative malnutrition due to menstrual blood loss and other reasons, particularly in terms of iron and vitamin D deficiency.²⁵ Ethnic differences may also have an impact on the development of preoperative malnutrition, and dietary habits and lifestyles vary among ethnic groups, resulting in differences in the type and degree of their nutritional deficiencies.²⁶

In summary, preoperative malnutrition is highly prevalent in patients those being considered for MBS, and its occurrence is influenced by multiple factors such as dietary habits, obesity itself, chronic inflammation, gender, and ethnicity. Tailoring nutritional interventions based on the severity of deficiencies is crucial. For mild deficiencies, oral supplements and dietary adjustments may suffice, while more severe cases may require higher doses, intravenous administration, or additional medical interventions. Correction of preoperative malnutrition is important to improve the preoperative status of patients and prevent postoperative complications.

Key Indicators and Methods of Preoperative Nutritional Assessment

Preoperative nutritional assessment for weight loss is an important link to ensure the safety of surgery and postoperative recovery. Key indicators and methods include comprehensive body composition analysis of patients, measurement of height and weight to calculate body mass index (BMI), assessment of body fat percentage, waist circumference, hip circumference and waist-to-hip ratio, and understanding of visceral fat area content, which are important indicators for judging the degree of obesity and health risks.²⁷ At the same time, micronutrient levels in blood, such as vitamin B1, vitamin B12, vitamin A, vitamin D, zinc, and copper, as well as mineral contents such as calcium, phosphorus, iron, potassium, sodium, and chloride, are measured to identify potential nutritional deficiencies.^28,29 In addition, the nutritional status and metabolic function of patients were assessed by blood tests to understand the content of macronutrients such as protein, fat, and carbohydrates in patients.³⁰ The evaluation methods mainly include detailed history inquiry, understanding the dietary habits, past disease history and drug use of patients; physical examination, observing the body size, skin condition and hair distribution of patients; laboratory tests, such as blood routine, blood biochemistry, liver and kidney function, blood glucose, blood lipid and endocrine hormone levels, such as insulin and thyroid hormone, to evaluate the metabolic status and endocrine function of patients.¹¹ Through comprehensive analysis of these indicators and methods obtained information, can comprehensively understand the nutritional status of patients, for the development of personalized preoperative nutritional intervention program to provide the basis, reduce the risk of postoperative complications, and promote postoperative recovery of patients.

It is also important to consider the educational and socioeconomic status of each individual with obesity during preoperative nutritional assessment. Not all individuals have the same access to preoperative weight loss programs, and some may not be able to afford these diets, which can sometimes be expensive. Social discrimination should also be taken into account when making these decisions, and certain social groups may need further support to ensure equitable access to care. At present, the commonly used nutritional risk screening tools are Nutritional Risk Screening Scale (NRS2002), Malnutrition Universal Screening Tools (MUST) and Mini-nutritional Assessment Short Form (MNA- SF). NRS2002 is recommended as the preferred tool for nutritional risk screening in inpatients by multiple nutrition societies internationally based on strong evidence-based evidence.³¹ However, obese patients, especially those with moderate to severe obesity and diabetes, often have micronutrient deficiencies before surgery,³² and nutritional screening using NRS-2002 is not accurately assessed at this time. Therefore, it is equally important for such patients to use nutritional assessment methods for nutritional screening. The nutritional status of the body was determined by subjective and objective methods such as clinical examination, anthropometry, biochemical examination, body composition measurement, and multiple comprehensive nutritional evaluations of the patients, so as to provide all-round nutritional guidance for the patients.³³

Type and Effect of Preoperative Dietary Management

Preoperative dietary management for MBS is an essential component of surgical success and aims to achieve moderate weight loss and improve surgical conditions. Common preoperative dietary patterns include energy restricted diets, low-carbohydrate ketogenic diets (LCKD), and dietary regimens incorporating ready-to-eat low-carbohydrate ketogenic products (RLCKPs).^34,35

Energy restricted diets are the most commonly recommended type of preoperative diet, which promotes weight loss by reducing caloric intake. However, this diet is associated with poorer long-term weight management outcomes and may lead to problems such as weight rebound, increased food craving, binge eating, emotional eating, malnutrition, and eating disorders, thereby reducing future success in changing eating behaviors. In addition, energy restricted diets may increase the likelihood of eating disorders, food consumption anxiety, and internalization of weight stigma, adversely affecting pre- and postoperative outcomes.³⁴

In contrast, LCKD showed better results in preoperative dietary management. Studies have shown that weight loss and left lateral liver segment (LLLS) volume reduction can be safely and effectively achieved with LCKD 4 weeks before surgery, thereby reducing the difficulty of surgery and the risk of complications. Most programs require people to follow a low calorie low carbohydrate diet prior to surgery for between 2 to 6 weeks to reduce the size of the liver and make the surgery safer. LCKD promotes lipolysis and energy expenditure by limiting carbohydrate intake and putting the body into a ketogenic state. However, long-term adherence to LCKD can be challenging because it has limited sweetness options and easily triggers a desire for traditional carbohydrate-rich foods.³⁵ In addition, it is important that patients have access to a dietitian to prepare for surgery. For instance, to help improve the quality of diet and eating patterns.

To address this issue, RLCKP was introduced into preoperative dietary management. RLCKP helps patients adhere more easily to LCKD by replicating the texture and flavor of traditional foods while maintaining low carbohydrate content. The study showed that a 4-week preoperative dietary regimen with RLCKP significantly reduced body weight and LLLS volume, with high patient compliance and satisfaction. The use of RLCKP improves adherence to ketogenic diet regimens and helps to improve the effect of preoperative diet management.³⁶ Patients following an LCKD may experience significant changes in hunger and mood. Studies have shown that while LCKD can effectively promote weight loss, some patients may report increased feelings of hunger or irritability during the initial adaptation phase. However, with proper support and counseling, these symptoms can be managed, and patient satisfaction can be improved. The use of RLCKP can further enhance patient compliance by providing more palatable and familiar food options, thereby reducing the psychological burden associated with dietary changes.³⁶

Overall, the types of preoperative dietary management for MBS are diverse, and different dietary regimens have their own advantages and disadvantages. Although energy-restricted diets are widely used, their long-term effects and effects on eating behavior cannot be ignored. LCKD and RLCKP dietary regimens have shown good results in promoting weight loss and improving surgical conditions, but further studies are still needed to optimize dietary regimens and improve patient compliance, so as to provide more scientific and effective preoperative dietary management strategies for MBS patients.

Necessity and Strategy of Preoperative Micronutrient Supplementation

MBS is an effective treatment for severe obesity and its related complications, however, preoperative and postoperative micronutrient deficiencies are prevalent in patients with MBS and may lead to a variety of complications, such as anemia, neurological diseases and metabolic bone diseases, which seriously affect the quality of life of patients and surgical outcomes. Therefore, preoperative micronutrient supplementation appears particularly necessary.^23,37 Preoperative micronutrient supplementation can not only correct the existing nutritional deficiency status of patients, optimize their nutritional status, create a good physiological basis for surgery, but also prevent the further deterioration of postoperative nutritional deficiency to a certain extent. Studies have shown that preoperative micronutrient deficiency is an important predictor of postoperative deficiency, and preoperative identification and treatment of these nutritional deficiencies can effectively prevent the deterioration of postoperative nutritional status, reduce the incidence of postoperative complications, and promote postoperative recovery of patients.²³

When developing preoperative micronutrient supplementation strategies, patients first need to undergo a comprehensive nutritional assessment, including a detailed history, physical examination, and relevant laboratory tests, such as blood routine, serum ferritin, vitamin D, folic acid, and vitamin B12 measurements, to accurately understand the specific nutritional deficiency of patients. On this basis, a personalized supplementation program is developed according to the type and degree of micronutrients deficient in the patient. For patients with vitamin D deficiency, oral vitamin D supplements can be used, and the daily dose of supplementation depends on serum 25 (OH) vitamin D levels, and it is generally recommended to maintain serum 25 (OH) vitamin D levels above 30 ng/mL.³⁸ For patients with iron deficiency, oral iron or intravenous iron supplementation can be given, and changes in serum ferritin, hemoglobin and other indicators should be monitored to assess the effect of supplementation; patients with folic acid and vitamin B12 deficiency can be corrected by oral or injection of the corresponding supplement.³⁹

In the selection of supplementary methods, oral supplements are the most commonly used modality and have the advantages of convenience and economy, but their absorption may be affected by factors such as gastrointestinal function and drug interactions of patients, so patients’ compliance and supplementary effects need to be closely monitored during supplementation, and other routes of administration such as intramuscular injection or intravenous infusion can be considered when necessary to improve the supplementary effect.⁴⁰ In addition, the timing of micronutrient supplementation before surgery also needs to be reasonably scheduled, and it is generally recommended that supplementation be started several weeks before surgery in order to give the patient sufficient time to correct the nutritional deficiency state while avoiding the potential risks resulting from supplementation near the time of surgery.⁴¹ It is worth noting that preoperative micronutrient supplementation is not a once and for all measure, and it is still necessary to continuously pay attention to the nutritional status of patients after surgery, and timely adjust the supplementation regimen according to the postoperative recovery and changes in nutritional requirements to ensure that patients can maintain a good nutritional status and promote health throughout the perioperative period and long-term follow-up after surgery.

Nutritional Management After MBS

Following MBS, patients often face a variety of nutritional deficiencies, and the types, mechanisms, and risk factors of these deficiencies are complex. These deficiencies not only affect the quality of life of patients, but may also lead to complications such as anemia, neurological diseases, and metabolic bone diseases in severe cases.⁴² The mechanism of nutritional deficiency is mainly related to physiological changes after surgery. On the one hand, surgery will change the anatomy of the digestive tract, such as reduced gastric capacity, reduced intestinal absorption area, etc., thus affecting the intake of food and nutrient absorption. For example, after gastric bypass surgery, food bypasses parts of the stomach and small intestine, resulting in decreased absorption of vitamin B12 and iron. On the other hand, patients may experience dyspeptic symptoms such as nausea and vomiting after surgery, further limiting the intake of food.⁴³ In addition, decreased gastric acid secretion after surgery can also affect the absorption of nutrients, such as vitamin B12 requires intrinsic factors in gastric acid to be absorbed. Finally, risk factors for postoperative nutritional deficiencies include patient gender, BMI, ethnicity, etc.⁴⁴ Female patients are more likely to present with iron deficiency and anemia due to physiological characteristics, such as menstrual blood loss. Patients with a higher degree of obesity may have nutritional deficiencies before surgery due to long-term unbalanced diet, and the risk is further increased after surgery.⁴⁵ People of different ethnic groups may also be at different risk of nutritional deficiencies due to differences in dietary habits and genetic factors. For example, people of certain ethnic groups may be more vulnerable to vitamin D deficiency.²⁶ Therefore, for patients with MBS, nutritional assessment and management before and after surgery are essential to prevent and correct nutritional deficiencies and ensure patient health and surgical outcomes. Additionally, post-bariatric hyperinsulinemic hypoglycemia (PBHH) is an increasingly recognized complication, especially after Roux-en-Y gastric bypass (RYGB). This condition can significantly affect the quality of life of patients and requires strict dietary instructions to avoid its occurrence. According to a recent study by Kehagias et al,⁴⁶ PBHH was observed in a considerable proportion of patients after laparoscopic Roux-en-Y gastric bypass, particularly among those with obesity and type 2 diabetes. The study highlighted the importance of close monitoring and dietary management to prevent and manage this complication. Patients are advised to follow a structured meal plan with frequent small meals and avoid high-carbohydrate foods to minimize the risk of hypoglycemia.

Long-term micronutrient deficiencies after MBS can lead to significant health issues, such as osteoporosis from chronic vitamin D deficiency and persistent anemia from iron deficiency.¹⁵ Regular nutritional monitoring and personalized supplementation are crucial for managing these deficiencies. Patients should undergo periodic screening for key nutrients (eg, iron, vitamin D, B12) and bone mineral density testing to assess osteoporosis risk.⁴⁷ Personalized supplementation plans should be developed based on individual deficiencies and adjusted over time. Additionally, dietary education and lifestyle modifications, such as maintaining a balanced diet and avoiding high-sugar foods, are essential for long-term health. Effective long-term nutritional management requires collaboration among dietitians, surgeons, endocrinologists, and psychologists. Each professional plays a critical role in supporting the patient’s nutritional needs and overall well-being.⁴⁸

The structure and habits of the diet also need to be adjusted after surgery. Patients should avoid foods high in sugar, fat, and salt and choose foods low in calories and fiber to help control weight and prevent the recurrence of obesity. At the same time, patients should be encouraged to develop good eating habits, such as regular quantitative eating, chewing slowly, etc., to promote digestion and absorption. Diversity in diet is also important and should include a variety of vegetables, fruits, whole grains, and high-quality protein sources to ensure that patients have access to comprehensive nutrition.⁴⁹

Postoperative nutritional monitoring is essential for patients receiving MBS, as surgery may lead to problems such as decreased food intake, poor nutritional absorption, etc., causing multiple nutritional deficiencies.⁴⁹ Trace element and vitamin levels, such as iron, zinc, copper, vitamin B1, B9, B12, D, A, E, etc., these nutrients are easily deficient after surgery, and their plasma concentrations need to be measured regularly to assess whether the patient has the corresponding nutritional deficiency; bone mineral density testing, monitoring bone mineral density changes by DEXA and other methods to assess the risk of osteoporosis, because vitamin D deficiency and calcium malabsorption may lead to osteoporosis; liver and kidney function indicators, such as transaminases, bilirubin, urea nitrogen, creatinine, etc., these indicators can reflect the overall metabolic status and organ function of patients and indirectly indicate nutritional status.⁵⁰ In terms of monitoring frequency, it is recommended to perform a comprehensive nutritional monitoring every 3 months in the first year after surgery, including all the above indicators, timely identify nutritional problems and intervene; the second year can be adjusted to biannual monitoring; and then at least once a year, focusing on blood routine, serum protein levels and trace elements, vitamin levels and other key indicators.⁵¹ The frequency of monitoring should be appropriately increased in patients at special nutritional risk, such as those with more postoperative complications, severely inadequate nutritional intake, or specific nutritional deficiency symptoms. Timely intervention for nutritional deficiencies is essential, and once nutritional deficiencies are detected, appropriate supplementation measures should be taken according to the type and degree of nutrients specifically deficient.⁵² For patients with iron deficiency anemia, oral iron or intravenous iron supplementation can be given if necessary, and dietary structure can be adjusted to increase iron-rich food intake; vitamin D deficiency requires vitamin D supplementation, oral or injectable formulations can be selected, and appropriate sun exposure can be encouraged to promote vitamin D synthesis in the body; for patients with protein malnutrition, nutritional status can be improved by increasing high-quality protein food intake or protein supplementation. At the same time, nutrition education should also be strengthened to guide patients to reasonably arrange their diets, avoid bad eating habits such as partial eclipse and picky eating, ensure balanced nutritional intake, and promote postoperative recovery.¹⁸ Perioperative nutritional management in MBS should be tailored to the unique needs of each patient, considering factors such as age, pre-existing comorbidities, and ethnic background. These factors can significantly influence nutritional outcomes and require specific attention.

Collaboration of multidisciplinary teams is essential during postoperative nutritional management. Professionals such as dietitians, surgeons, endocrinologists, and psychologists should participate in the development of nutritional assessment and management plans for patients. Dietitians are responsible for providing personalized dietary advice and nutrition education, surgeons and endocrinologists adjust treatment options according to the specific circumstances of patients, and psychologists help patients cope with psychological problems that may occur after surgery, such as anxiety and depression, which may affect the patient ‘dietary behavior and nutritional status.⁵²

Perioperative nutritional management also varies between specific patient groups in metabolic versus bariatric surgery. Elderly patients may have more complex nutritional problems due to physiological hypofunction. With age, gastrointestinal function decreases, the absorption capacity of nutrients weakens, and deficiencies of nutrients such as protein, vitamin B12, and calcium are more likely to occur. Therefore, more meticulous examination of these nutrient levels is required during preoperative nutritional assessment. At the same time, elderly patients may have sarcopenia, and muscle mass and function should be assessed emphatically preoperatively and judged by measuring grip strength, gait speed, and other indicators.⁵³ Older patients recover more slowly after surgery and may have longer hospital stays. Postoperative nutritional support should pay more attention to maintaining muscle mass and improving physical function, and appropriately increase protein intake, such as by whey protein supplementation. In addition, due to the decreased ability of the elderly to metabolize and excrete drugs, attention should be paid to drug interactions when nutritional preparations are supplemented postoperatively to avoid affecting the efficacy of other drugs or increasing adverse reactions.⁵⁴ For diabetic patients, preoperative glycemic control is essential. Blood glucose management should be optimized before metabolic and bariatric surgery to avoid increased surgical risk due to hyperglycemia. In preoperative dietary management, in addition to conventional low-calorie diets, the proportion and type of carbohydrate intake can be appropriately adjusted, and foods with low glycemic index can be selected to help better control blood glucose. At the same time, blood glucose changes should be closely monitored, hypoglycemic drug doses should be adjusted according to blood glucose levels, and hypoglycemic regimens should be optimized in cooperation with endocrinologists if necessary.⁹ Cardiac function and nutritional status should be assessed preoperatively in patients with cardiovascular disease. In nutritional management, sodium intake should be restricted to reduce edema and cardiac burden. At the same time, adequate protein intake is ensured to maintain myocardial function. For patients with hypertension, preoperative diet should pay attention to blood pressure control, avoid high-salt, high-fat foods, and increase the intake of foods rich in potassium and magnesium, such as green leafy vegetables and fruits, which helps to reduce blood pressure.²⁹ Diet habits vary significantly among ethnic groups, which can influence the development of nutritional management programs. The diet of people in the Mediterranean region is rich in olive oil, fish, vegetables and fruits, and this diet is rich in unsaturated fatty acids, vitamins and minerals. For patients from the Mediterranean region, preoperative dietary management can appropriately adjust the intake ratio of olive oil and fish to meet nutritional needs. However, some people in Asia mainly eat cereals, and vegetable and fruit intake is relatively small, and it is necessary to increase vegetable and fruit intake and improve nutritional structure before surgery.⁴⁴

In conclusion, nutritional management after MBS is a long-term and integrated process that requires the joint efforts of patients, families, and medical teams. Through reasonable dietary modification, nutritional supplementation and multidisciplinary collaboration, the occurrence of postoperative nutritional deficiency and other complications can be effectively prevented, and the health recovery and quality of life of patients can be promoted.

Challenges in Perioperative Nutritional Management

Perioperative nutritional management plays a crucial role in MBS, but it also faces many challenges. Malnutrition and micronutrient deficiencies are prevalent in obese patients preoperatively. Preoperative vitamin D, iron, folic acid, vitamin B12 and other nutrients deficiencies are high due to long-term unbalanced diets and obesity-related physiological changes, such as reduced bioavailability of vitamin D and chronic inflammation affecting iron absorption. Obese patients often have a long history of restricted diets and fluctuations in body weight, resulting in depletion of fat-free mass (FFM), further exacerbating the risk of malnutrition.⁵⁵ The assessment and optimization of preoperative nutritional status is particularly important, but there is no uniform consensus and standard in the definition of preoperative nutritional evaluation, the selection of screening markers, the determination of pathological cut-off values, and the dose of nutritional supplements, which poses a challenge to clinical practice.

Entering the postoperative phase, challenges in nutritional management escalated further. Patients are more prone to nutritional deficiencies after MBS due to factors such as reduced food intake, anatomical changes leading to inadequate nutrient absorption, and decreased gastric acid and endoplasmic reticulum secretion. Especially for some malabsorptive procedures, such as biliopancreatic diversion plus duodenal switch (BPD-DS), the risk of postoperative nutritional deficiencies is higher.⁵⁵ Postoperative nutritional deficiencies not only affect the quality of life of patients, but may also lead to serious complications, such as anemia, neurological diseases and metabolic bone diseases. Therefore, long-term and even life-long monitoring and supplementation of nutrients are required after surgery to prevent and correct nutritional deficiencies. However, the individual differences of patients after surgery are large, different surgical types, basic nutritional status of patients, dietary habits and other factors will affect the effect of nutritional management, how to develop individualized nutritional supplementation program is still a difficult problem.

Future research directions can be developed from the following aspects: First, to strengthen standardized and refined studies of preoperative nutritional assessment. To develop more accurate and comprehensive preoperative nutritional assessment tools and indicators to identify cut-off values for different nutrient deficiencies in order to better identify patients with preoperative malnutrition and provide a basis for preoperative nutritional intervention. Second, to deeply explore the best program of preoperative nutritional intervention. To investigate the effects of different nutritional supplements on preoperative nutritional status and prevention of postoperative nutritional deficiency, and provide more scientific and effective preoperative nutritional intervention strategies for clinical practice. In addition, optimization of postoperative nutritional management is also the focus of future research. Further studies are needed to investigate changes in nutritional requirements at different stages after surgery, explore individualized nutritional supplementation regimens, and how to improve patient compliance with nutritional supplementation. At the same time, attention should also be paid to the impact of postoperative nutritional deficiency on the long-term health of patients, and long-term follow-up studies should be carried out to evaluate the impact of different nutritional management strategies on postoperative complications, quality of life and long-term prognosis of patients, providing a strong evidence-based basis for the continuous improvement of perioperative nutritional management.

Summary

Perioperative nutritional management has a crucial role in MBS. Preoperative nutritional assessment and intervention are essential to improve surgical success. Through preoperative nutritional support, the nutritional status of patients can be improved and the incidence of postoperative complications can be reduced, thereby improving the success rate of surgery. Nutritional management is also essential after surgery. Following MBS, patients may be at risk of deficiencies in nutrients such as protein, vitamin D, calcium, iron, vitamin B12, and folic acid. Deficiencies in these nutrients not only affect the physical health of patients, but may also lead to a decrease in quality of life. Good nutritional management can further enhance this improvement, help patients better adapt to the postoperative lifestyle, and improve their quality of life. In order to further optimize the nutritional management strategy during the perioperative period of MBS, future research and practice need to be explored and improved in the following aspects: First, a more personalized and precise nutritional management program needs to be developed and adjusted according to the specific circumstances and nutritional needs of patients. Second, collaboration among multidisciplinary teams, including dietitians, surgeons, endocrinologists, etc., should be strengthened to jointly develop and implement nutrition management programs. In addition, education and guidance for patients and their families should be strengthened to improve their awareness and compliance with the importance of nutritional management. Through these efforts, the nutritional needs of patients in the perioperative period can be better met, and the success rate of surgery and the long-term quality of life of patients can be improved. Moreover, it is important to address the significant challenges discussed in this review, such as the high prevalence of preoperative malnutrition and the complexity of postoperative nutritional deficiencies. Future research is essential to develop more accurate preoperative nutritional assessment tools and personalized postoperative nutritional supplementation strategies to optimize perioperative nutritional management.

Data Sharing Statement

All data generated or analyzed during this study are included in this published article.

Ethics Approval and Consent to Participate

An ethics statement is not applicable because this study is based exclusively on published literature.

Funding

There is no funding to report.

Disclosure

The authors have no personal, financial, commercial, or academic conflicts of interest in this study.

References

1. Gerardo G, Peterson N, Goodpaster K, Heinberg L. Depression and obesity. Curr Obes Rep. 2025;14(1):5. PMID: 39752052. doi:10.1007/s13679-024-00603-x

2. Yu J, Chen S, Yang J, et al. Childhood and adolescent overweight/obesity prevalence trends in Jiangsu, China, 2017-2021: an age-period-cohort analysis. Public Health Nurs. 2024. PMID: 39737852. doi:10.1111/phn.13517.

3. Wong HJ, Lin NHY, Teo YH, et al. Anti-diabetic effects of GLP-1 receptor agonists on obese and overweight patients across diabetes status, administration routes, treatment duration and baseline characteristics: a systematic review. Diabetes Obes Metab. 2025;27(4):1648–1659. PMID: 39726212. doi:10.1111/dom.16136

4. Wang M, Flexeder C, Harris CP, et al. Accelerometry-assessed sleep clusters and obesity in adolescents and young adults: a longitudinal analysis in GINIplus/LISA birth cohorts. World J Pediatr. 2025. PMID: 39754701. doi:10.1007/s12519-024-00872-5.

5. Marketdata Enterprises LLC. The U.S. Weight Loss and Diet Control Market. 17th. Tampa, FL: Marketdata Enterprises LLC. 2023. Report No.: 5313560.

6. Yousefi R, Ben-Porat T, O’Neill J, et al. Understanding the components of eating behaviour-focused weight management interventions adjunct to metabolic bariatric surgery: systematic review of published literature. Curr Obes Rep. 2025;14(1):3. PMID: 39753946. doi:10.1007/s13679-024-00596-7

7. Kehagias D, Georgopoulos N, Habeos I, Lampropoulos C, Mulita F, Kehagias I. The role of the gastric fundus in glycemic control. Hormones. 2023;22(2):151–163. PMID: 36705877. doi:10.1007/s42000-023-00429-7

8. Morton JM. 2015 American society for metabolic and bariatric surgery presidential address. Surg Obes Relat Dis. 2024;30:S1550–7289(24)00917–1. PMID: 39732585. doi:10.1016/j.soard.2024.11.008

9. Mechanick JI, Youdim A, Jones DB, et al. American Association of Clinical Endocrinologists; Obesity Society; American Society for Metabolic & Bariatric Surgery. Clinical practice guidelines for the perioperative nutritional, metabolic, and nonsurgical support of the bariatric surgery patient–2013 update: cosponsored by American association of clinical endocrinologists, the obesity society, and American society for metabolic & bariatric surgery. Obesity. 2013;1(01):S1–27. PMID: 23529939; PMCID: PMC4142593. doi:10.1002/oby.20461

10. Stenberg E, Reis Falcão LF D, O’Kane M, et al. Guidelines for perioperative care in bariatric surgery: Enhanced Recovery After Surgery (ERAS) society recommendations: a 2021 update. World J Surg. 2022;46(4):729–751. PMID: 34984504; PMCID: PMC8885505. doi:10.1007/s00268-021-06394-9

11. Özkan AE, Koca N, Tekeli AH. Assessment of nutritional status and clinical outcomes: a comprehensive retrospective analysis of critically ill patients. Medicine. 2023;102(44):e36018. PMID: 37932978; PMCID: PMC10627690. doi:10.1097/MD.0000000000036018

12. Firman CH, Mellor DD, Unwin D, Brown A. Does a ketogenic diet have a place within diabetes clinical practice? Review of current evidence and controversies. Diabetes Ther. 2024;15(1):77–97. PMID: 37966583; PMCID: PMC10786817. doi:10.1007/s13300-023-01492-4

13. Mechanick JI, Apovian C, Brethauer S, et al. Clinical practice guidelines for the perioperative nutrition, metabolic, and nonsurgical support of patients undergoing bariatric procedures – 2019 update: cosponsored by American Association of Clinical Endocrinologists/American College of Endocrinology, The Obesity Society, American Society for Metabolic & Bariatric Surgery, Obesity Medicine Association, and American Society of Anesthesiologists – executive summary. Endocr Pract. 2019;25(12):1346–1359. PMID: 31682518. doi:10.4158/GL-2019-0406

14. Lewis CA, de Jersey S, Seymour M, Hopkins G, Hickman I, Osland E. Iron, vitamin B12, folate and copper deficiency after bariatric surgery and the impact on anaemia: a systematic review. Obes Surg. 2020;30(11):4542–4591. PMID: 32785814. doi:10.1007/s11695-020-04872-y

15. Musella M, Berardi G, Vitiello A, et al. Vitamin D deficiency in patients with morbid obesity before and after metabolic bariatric surgery. Nutrients. 2022;14(16):3319. PMID: 36014825; PMCID: PMC9416433. doi:10.3390/nu14163319

16. Sander J, Torensma B, Siepe J, et al. Assessment of preoperative multivitamin use on the impact on micronutrient deficiencies in patients with obesity prior to metabolic bariatric surgery. Obes Surg. 2025. PMID: 40199822. doi:10.1007/s11695-025-07853-1.

17. Jáuregui-Lobera I. Iron deficiency and bariatric surgery. Nutrients. 2013;5(5):1595–1608. PMID: 23676549; PMCID: PMC3708339. doi:10.3390/nu5051595

18. Grace C, Vincent R, Aylwin SJ. High prevalence of vitamin D insufficiency in a United Kingdom urban morbidly obese population: implications for testing and treatment. Surg Obes Relat Dis. 2014;10(2):355–360. PMID: 24411192. doi:10.1016/j.soard.2013.07.017

19. Flores L, Moizé V, Ortega E, et al. Prospective study of individualized or high fixed doses of vitamin D supplementation after bariatric surgery. Obes Surg. 2015;25(3):470–476. PMID: 25086955. doi:10.1007/s11695-014-1393-9

20. Gagnon C, Schafer AL. Bone health after bariatric surgery. JBMR Plus. 2018;2(3):121–133. PMID: 30283897; PMCID: PMC6124196. doi:10.1002/jbm4.10048

21. Cornejo-Pareja I, Clemente-Postigo M, Tinahones FJ. Metabolic and endocrine consequences of bariatric surgery. Front Endocrinol. 2019;10:626. PMID: 31608009; PMCID: PMC6761298. doi:10.3389/fendo.2019.00626

22. Ba F, Siddiqi ZA. Neurologic complications of bariatric surgery. Rev Neurol Dis. 2010;7(4):119–124. PMID: 21206427.

23. Reytor-González C, Frias-Toral E, Nuñez-Vásquez C, et al. Preventing and managing pre- and postoperative micronutrient deficiencies: a vital component of long-term success in bariatric surgery. Nutrients. 2025;17(5):741. PMID: 40077612; PMCID: PMC11902093. doi:10.3390/nu17050741

24. Sayadi Shahraki M, Khalili N, Yousefvand S, Sheikhbahaei E, Shahabi Shahmiri S. Severe obesity and vitamin D deficiency treatment options before bariatric surgery: a randomized clinical trial. Surg Obes Relat Dis. 2019;15(9):1604–1611. PMID: 31402293. doi:10.1016/j.soard.2019.05.033

25. Al-Mutawa A, Anderson AK, Alsabah S, Al-Mutawa M. Nutritional status of bariatric surgery candidates. Nutrients. 2018;10(1):67. PMID: 29324643; PMCID: PMC5793295. doi:10.3390/nu10010067

26. Abu-Saad K, Murad H, Lubin F, et al. Jews and Arabs in the same region in Israel exhibit major differences in dietary patterns. J Nutr. 2012;142(12):2175–2181. PMID: 23096004. doi:10.3945/jn.112.166611

27. Stegenga H, Haines A, Jones K, Wilding J; Guideline Development Group. Identification, assessment, and management of overweight and obesity: summary of updated NICE guidance. BMJ. 2014;349:g6608. PMID: 25430558. doi:10.1136/bmj.g6608

28. Parrott J, Frank L, Rabena R, Craggs-Dino L, Isom KA, Greiman L. American society for metabolic and bariatric surgery integrated health nutritional guidelines for the surgical weight loss patient 2016 update: micronutrients. Surg Obes Relat Dis. 2017;13(5):727–741. PMID: 28392254. doi:10.1016/j.soard.2016.12.018

29. O’Kane M, Parretti HM, Pinkney J, et al. British obesity and metabolic surgery society guidelines on perioperative and postoperative biochemical monitoring and micronutrient replacement for patients undergoing bariatric surgery-2020 update. Obes Rev. 2020;21(11):e13087. PMID: 32743907; PMCID: PMC7583474. doi:10.1111/obr.13087

30. Lim HS, Kim YJ, Lee J, Yoon SJ, Lee B. Establishment of adequate nutrient intake criteria to achieve target weight loss in patients undergoing bariatric surgery. Nutrients. 2020;12(6):1774. PMID: 32545878; PMCID: PMC7353322. doi:10.3390/nu12061774

31. Qin X, Zhang Z, Chen L, Wu G. Gastrointestinal surgery group, Chinese medical association surgery branch, colorectal surgery group, Chinese medical association surgery branch, gastrointestinal surgery committee, Chinese medical doctor association surgery branch. Chinese expert consensus on perioperative whole-course nutrition management for gastrointestinal surgery (2021 Edition). Chinese J Pract Sur. 2021;41(10):1111–1125. doi:10.19538/j.cjps.issn1005-2208.2021.10.05

32. Jans G, Matthys C, Bogaerts A, et al. Maternal micronutrient deficiencies and related adverse neonatal outcomes after bariatric surgery: a systematic review. Adv Nutr. 2015;6(4):420–429. PMID: 26178026; PMCID: PMC4496736. doi:10.3945/an.114.008086

33. Li ZJ, Chen W. Optimizing perioperative nutrition management in enhanced recovery after surgery. Zhonghua Wai Ke Za Zhi. 2019;57(7):513–516. PMID: 31269613. doi:10.3760/cma.j.issn.0529-5815.2019.07.007

34. Nordmo M, Danielsen YS, Nordmo M. The challenge of keeping it off, a descriptive systematic review of high-quality, follow-up studies of obesity treatments. Obes Rev. 2020;21(1):e12949. PMID: 31675146. doi:10.1111/obr.12949

35. Khalooeifard R, Rahmani J, Ghoreishy SM, Tavakoli A, Najjari K, Talebpour M. Evaluate the effects of different types of preoperative restricted calorie diets on weight, body mass index, operation time and hospital stay in patients undergoing bariatric surgery: a systematic review and meta analysis study. Obes Surg. 2024;34(1):236–249. PMID: 38052747. doi:10.1007/s11695-023-06973-w

36. Santella B, Mingo M, Papp A, et al. Safety and effectiveness of a 4-week diet on low-carb ready-to-eat ketogenic products as preoperative care treatment in patients scheduled for metabolic and bariatric surgery. Nutrients. 2024;16(22):3875. PMID: 39599661; PMCID: PMC11597797. doi:10.3390/nu16223875

37. Kaberi-Otarod J, Still CD, Wood GC, Benotti PN. Iron treatment in patients with iron deficiency before and after metabolic and bariatric surgery: a narrative review. Nutrients. 2024;16(19):3350. PMID: 39408317; PMCID: PMC11478352. doi:10.3390/nu16193350

38. Pludowski P, Grant WB, Karras SN, Zittermann A, Pilz S. Vitamin D supplementation: a review of the evidence arguing for a daily dose of 2000 international units (50 µg) of vitamin D for adults in the general population. Nutrients. 2024;16(3):391. PMID: 38337676; PMCID: PMC10857599. doi:10.3390/nu16030391

39. Lo JO, Benson AE, Martens KL, et al. The role of oral iron in the treatment of adults with iron deficiency. Eur J Haematol. 2023;110(2):123–130. PMID: 36336470; PMCID: PMC9949769. doi:10.1111/ejh.13892

40. Magali Sanchez AM, Pampillón N, Abaurre M. Omelanczuk pe. deficiencia de hierro en el preoperatorio de cirugía bariátrica: diagnóstico y tratamiento [pre-operative iron deficiency in bariatric surgery: diagnosis and treatment]. Nutr Hosp. 2015;32(1):75–79. PMID: 26262699. doi:10.3305/nh.2015.32.1.8871

41. Hassan M, Barajas-Gamboa JS, Kanwar O, et al. The role of dietitian follow-ups on nutritional outcomes post-bariatric surgery. Surg Obes Relat Dis. 2024;20(4):407–412. PMID: 38158312. doi:10.1016/j.soard.2023.10.017

42. Noser MS, Boll DT, Lazaridis II, et al. Opportunistic quantitative computed tomography assessing bone mineral density in patients with laparoscopic Roux-En-Y-Gastric bypass metabolic surgery throughout a 5-year observation window. J Comput Assist Tomogr. 2024. PMID: 39631733. doi:10.1097/RCT.0000000000001705.

43. Angrisani L, Santonicola A, Iovino P, et al. Collaborative Study Group for the IFSO Worldwide Survey. IFSO worldwide survey 2020-2021: current trends for bariatric and metabolic procedures. Obes Surg. 2024;34(4):1075–1085. PMID: 38438667; PMCID: PMC11026210. doi:10.1007/s11695-024-07118-3

44. Lee PC, Ganguly S, Dixon JB, Tan HC, Lim CH, Tham KW. Nutritional deficiencies in severe obesity: a multiethnic Asian cohort. Obes Surg. 2019;29(1):166–171. PMID: 30191504. doi:10.1007/s11695-018-3494-3

45. Al-Mutawa A, Al-Sabah S, Anderson AK, Al-Mutawa M. Evaluation of nutritional status post laparoscopic sleeve gastrectomy-5-year outcomes. Obes Surg. 2018;28(6):1473–1483. PMID: 29197046. doi:10.1007/s11695-017-3041-7

46. Kehagias D, Lampropoulos C, Vamvakas SS, Kehagia E, Georgopoulos N, Kehagias I. Post-bariatric hypoglycemia in individuals with obesity and type 2 diabetes after laparoscopic Roux-en-Y gastric bypass: a prospective cohort study. Biomedicines. 2024;12(8):1671. PMID: 39200136; PMCID: PMC11351344. doi:10.3390/biomedicines12081671

47. Gudzune KA, Huizinga MM, Chang HY, Asamoah V, Gadgil M, Clark JM. Screening and diagnosis of micronutrient deficiencies before and after bariatric surgery. Obes Surg. 2013;23(10):1581–1589. PMID: 23515975; PMCID: PMC3740071. doi:10.1007/s11695-013-0919-x

48. Bednarczuk B, Czekajło-Kozłowska A. Role of nutritional support provided by qualified dietitians in the prevention and treatment of non-communicable diseases. Rocz Panstw Zakl Hig. 2019;70(3):235–241. PMID: 31515982. doi:10.32394/rpzh.2019.0080

49. Chinaka U, Fultang J, Ali A, Rankin J, Bakhshi A. Pre-specified weight loss before bariatric surgery and postoperative outcomes. Cureus. 2020;12(12):e12406. PMID: 33542862; PMCID: PMC7849210. doi:10.7759/cureus.12406

50. Sherf Dagan S, Goldenshluger A, Globus I, et al. Nutritional recommendations for adult bariatric surgery patients: clinical practice. Adv Nutr. 2017;8(2):382–394. PMID: 28298280; PMCID: PMC5347111. doi:10.3945/an.116.014258

51. Roberts R, Williams DM, Min T, Barry J, Stephens JW. Benefits in routinely measured liver function tests following bariatric surgery: a retrospective cohort study. J Diabetes Metab Disord. 2023;22(2):1763–1768. PMID: 37975098; PMCID: PMC10638127. doi:10.1007/s40200-023-01311-4

52. Järvholm K, Janson A, Henfridsson P, Neovius M, Sjögren L, Olbers T. Metabolic and bariatric surgery for adolescents with severe obesity: benefits, risks, and specific considerations. Scand J Surg. 2024;17:14574969241297517. PMID: 39552134. doi:10.1177/14574969241297517

53. Muscaritoli M, Anker SD, Argilés J, et al. Consensus definition of sarcopenia, cachexia and pre-cachexia: joint document elaborated by Special Interest Groups (SIG) “cachexia-anorexia in chronic wasting diseases” and “nutrition in geriatrics”. Clin Nutr. 2010;29(2):154–159. PMID: 20060626. doi:10.1016/j.clnu.2009.12.004

54. Morley JE, Argiles JM, Evans WJ, et al. Society for sarcopenia, cachexia, and wasting disease. J Am Med Dir Assoc. 2010;11(6):391–396. PMID: 20627179; PMCID: PMC4623318. doi:10.1016/j.jamda.2010.04.014

55. Stefanakis K, Kokkorakis M, Mantzoros CS. The impact of weight loss on fat-free mass, muscle, bone and hematopoiesis health: implications for emerging pharmacotherapies aiming at fat reduction and lean mass preservation. Metabolism. 2024;161:156057. PMID: 39481534. doi:10.1016/j.metabol.2024.156057