In just four weeks, a daily 500 mg dose of carrot-derived fiber enriched beneficial Bifidobacteria, firmed stools, and primed immune defenses, offering a new approach to strengthening gut and overall health.
Study: Carrot Rhamnogalacturonan-I Supplementation Shapes Gut Microbiota and Immune Responses: A Randomised Trial in Healthy Adults. Image credit: Anna_Pustynnikova/Shutterstock.com
A randomized controlled trial involving healthy adults demonstrates that the carrot-derived dietary fiber rhamnogalacturonan-I can improve gut microbiota composition, increase dendritic cell activation, support intestinal function, and immune responses within a short supplementation period. The trial findings are published in the journal Microorganisms.
Background
Dietary fibers are essential food components that play a crucial role in preventing various chronic diseases, including obesity, diabetes, cardiovascular disease, and colorectal cancer. The rapidly growing popularity of Western-type diets worldwide has become a major public health concern, as these diets contain very low amounts of dietary fiber.
Inadequate intake of dietary fibers can negatively affect the composition and diversity of the gut microbiota, leading to reduced formation of beneficial microbial metabolites, including short-chain fatty acids.
Among various dietary fibers, gut bacteria can ferment water-soluble fibers to produce bioactive metabolites, which act systemically to supply energy to other gut microorganisms and host tissues and organs. Dietary fibers can also improve gut microbiota composition and diversity, which is associated with several health benefits, including improved gut barrier integrity and enhanced immune responses against pathogens.
Given the significant association of dietary fibers with gut and overall health, this randomized controlled trial explored gut microbiota-modulating and immunomodulating effects of carrot-derived rhamnogalacturonan-I (RG-I) in healthy adults. Carrot-derived RG-I is a pectic polysaccharide with potential prebiotic and immunomodulatory properties.
Trial design
The trial enrolled 54 healthy adults aged 18 to 70. They were randomly assigned to the intervention group or the control group to receive 500 milligrams of carrot-derived RG-I or maltodextrin (placebo) per day for four weeks, respectively. To balance the groups, participants were stratified before being randomized according to their habitual fiber intake and baseline Bifidobacteria levels.
The gut health and overall well-being of the participants were assessed using questionnaires. Fecal samples were collected to assess the growth of beneficial bacteria, including Bifidobacterium spp., and the levels of short-chain fatty acids, inflammation markers, and immune cells.
For a mechanistic overview, the trial assessed the impact of RG-I on intestinal barrier integrity and immune cell activation using preclinical in vitro and ex vivo models.
Key findings
The trial findings revealed that RG-I is well-tolerated among participants and is associated with excellent compliance. Two participants in the intervention group withdrew due to unrelated antibiotic use rather than study side effects.
Bifidobacteria counts in fecal samples revealed a significant increase among intervention group participants, peaking after three weeks of supplementation. Bifidobacteria are one of the most abundant and beneficial bacterial genera in the gastrointestinal tract.
The analysis of fecal microbial metabolites revealed that the four-week RG-I supplementation led to a small but significant increase in isobutyric acid levels, a branched short-chain fatty acid with potential health benefits. It is produced in the gut through gut bacteria-mediated fermentation of non-digestible dietary fibers. No other short-chain fatty acids showed significant changes, and untargeted metabolomics (LA-REIMS) did not detect treatment-related differences.
The immunological analysis revealed that RG-I significantly increases the proportion of circulating myeloid dendritic cells expressing activation markers after four weeks of supplementation. The authors emphasize that this finding reflects immune cell activation rather than broad clinical immune improvements and note that plasmacytoid dendritic cells and monocytes showed non-significant upward trends. Further research is needed to determine the functional relevance of these effects.
The preclinical in vitro and ex vivo experiments revealed that RG-I and its fermented byproducts can protect intestinal barrier integrity under stressful conditions.
Additional findings included a small but statistically significant reduction in diarrhea scores, interpreted as firmer stool consistency, and distinct shifts in patterns of physical activity: vigorous activity was maintained in the RG-I group but declined in the placebo group. In contrast, moderate activity increased in the placebo group and decreased in the RG-I group.
Significance
This randomized controlled trial demonstrates that carrot-derived dietary fiber RG-I can improve gut microbiota composition and intestinal barrier integrity and modulate immune cell activation in healthy adults within a short supplementation period.
This trial’s low daily dose of RG-I (500 milligrams per day) ensures good compliance and convenience. This dose is well-tolerated and does not trigger gastrointestinal discomfort such as bloating or flatulence, which are common complaints with some prebiotic fibers.
According to the findings, RG-I supplementation causes a gradual and significant increase in Bifidobacteria counts over four weeks. Bifidobacteria are well-known for various health benefits, including improved gut health, production of beneficial metabolites and vitamins, growth of other beneficial gut bacteria via cross-feeding, prevention of gastrointestinal disorders, and improved antimicrobial responses.
The observed increase in Bifidobacteria count may be attributed to the RG-I backbone with arabinose- and galactose-rich side chains selectively used by this bacterial species. This interpretation is further supported by the observation that RG-I consistently increases the growth of Bifidobacterium longum and Bifidobacterium adolescentis by supplying oligosaccharides released from these side chains by primary degraders.
The trial could not find any significant beneficial impact of RG-I supplementation on the levels of short-chain fatty acids, except for a small but significant increase in isobutyric acid in fecal samples. This absence of detectable effects might be explained by the fact that more than 95% of short-chain fatty acids are absorbed in the large bowel and therefore cannot be detected in fecal samples.
Regarding immunomodulatory effects, the trial reported that RG-I supplementation increases the expression of activation markers on circulatory dendritic cells, considered the first line of defense against invading pathogens. Further research is needed to examine whether this activation occurs through direct interactions of immune cells with RG-I in the gut.
The authors also note that participants in this study already had relatively high dietary fiber intake (25–28 g/day on average), which may influence how generalizable the findings are to populations with lower baseline fiber intake.
Overall, the trial findings highlight the utility of carrot-derived RG-I as a safe, low-dose dietary intervention to improve gut health and overall well-being in healthy adult individuals.
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