Eating more animal protein may slightly lower cancer mortality

New findings challenge the long-held belief that animal protein raises mortality risk, showing no harm for longevity and even a small cancer-protective effect in US adults.

Study: Animal and plant protein usual intakes are not adversely associated with all-cause, cardiovascular disease–, or cancer-related mortality risk: an NHANES III analysis. Image credit: Victoria 1/Shutterstock.com

A recent study in Applied Physiology, Nutrition, and Metabolism investigated the impact of animal and plant protein intakes on mortality from all causes, cancer, and cardiovascular disease (CVD). Researchers observed no differential associations between mortality risk and dietary proteins derived from plants and animals. Still, they found that animal protein intake was modestly associated with a lower cancer mortality risk.

Protein intake and health

In the US and Canada, the recommended dietary allowance (RDA) for protein is set at 0.8 g protein/kg/day for good health. However, the dietary protein range within the acceptable macronutrient distribution ranges (AMDR) is several times higher than the RDA. There is no clear recommendation on how much dietary protein intake is beneficial, particularly in the older population.

Research has shown that higher animal protein consumption increases mortality risk due to cancer and CVD. In contrast, plant protein intake has been linked to higher health benefits and lower mortality risks. A previous study used the Third National Health and Nutrition Examination Survey 1988–1994 (NHANES III) data, revealing the association between higher protein intake and a significant increase in overall mortality. This study also showed that higher protein consumption could lead to a fourfold increased risk of cancer in adults aged 50–65 years. However, these outcomes would vary depending on whether or not the protein consumed was obtained from plants.

Mechanistically, the proposed cancer-promoting effects of high protein intake are linked to insulin-like growth factor 1 (IGF-1). A linear association between protein intake and circulating IGF-1 levels has been documented. Therefore, a lower protein intake may reduce the risk of IGF-1-related cancer and all-cause mortality. Interestingly, meta-analyses have indicated a U-shaped relationship between IGF-1 and mortality, i.e., elevated mortality risks in individuals with lower or higher IGF-1 levels.

Considering the heterogeneous outcomes regarding the health effects of protein intake, more research is required to assess the relationship between usual intake of animal and plant protein and cancer, as well as all causes and CVD mortality risk in adults of various age groups.

About the study

The current study tested whether animal protein intake might increase mortality risk, particularly in middle-aged adults, and whether plant protein intake might be protective. The researchers also hypothesized that circulating IGF-1 would not be associated with mortality.

NHANES III survey data from 1988 to 1994 and protein intake data on all adults above 19 years old were included. Initially, 15,937 participants were screened; 7,483 were men, and 8,454 were women. Individuals with unreliable data, no follow-up reports, and pregnant or lactating females were excluded.

Total calories, protein, animal protein, plant protein, total fats, and carbohydrates were estimated and modelled using the multivariate Markov Chain Monte Carlo (MCMC) method. Nutrient content was estimated by linking food composition data provided by the USDA Nutrient Database for Standard Reference (SR). Hazard models were run only with participants with a complete set of covariates.

The National Cattlemen’s Beef Association funded the study, although the authors reported that the sponsor had no role in its design, analysis, or interpretation.

Study findings

The current study indicated that animal protein intake was not linked with increased risk of mortality due to cancer, all-cause, or CVD. However, age, smoking, and a sedentary lifestyle were identified as expected risk factors for all-cause mortality in adjusted models.  Regular consumption of animal protein was associated with a modest but significant inverse association with cancer mortality.

No association was observed between usual plant protein consumption and all-cause, CVD, or cancer mortality risk. The result remained unaltered, even when mortality, either all-cause, CVD-, or cancer-related, was determined in adults between 19 and 65 years of age or those older than 65.

Participants consuming plant proteins exhibited no association between protein intake and all-cause, CVD, and cancer mortality risk when assessed on a 5- or 10 g increment basis. There was no association with all-cause or CVD mortality for animal protein when evaluated on a 5- or 10 g increment basis. Still, a significant inverse association was observed with cancer mortality. A simultaneous animal and plant protein introduction into the hazard model demonstrated similar results.

The current study observed no association between IGF-1 concentrations and the risk of all-cause, cancer, and CVD mortality. Hazard ratio (HR) analysis in all adults demonstrated no significant link between usual protein intakes and all-cause mortality risk, CVD-related risk, or cancer mortality risk. There was no change in HR between the younger and older cohorts for animal protein or plant protein for all-cause, CVD-, and cancer-related mortality.

In contrast to previous study findings, this study found no beneficial mortality outcomes with increasing plant protein consumption. A modest but significant protective relationship was observed between usual animal protein intake and cancer mortality. Such an association was absent for the usual intake of plant protein.

Conclusions

The current study demonstrated no association between either animal or plant proteins with all-cause or CVD mortality risk. No association between IGF-1 concentration and all-cause, CVD, and cancer-related mortality risk was observed even in the older population. Increasing animal protein intake showed a small but statistically significant reduction in cancer mortality risk.

The authors indicated several limitations, including the lack of comparator nutrients in the analysis. Furthermore, since IGF-1 results were associated with only a sub-sample of the population, this could underestimate the actual number of mortality events. Future research must include biomarkers and urinary urea nitrogen to assess the impact of protein intake.