Animal and plant proteins: is there a link with mortality?

The impact of protein consumption, whether from animal or plant sources, on long-term health, and in particular on mortality, is one of the most hotly debated topics in human nutrition. It lies at the intersection of concerns related to chronic disease prevention, official dietary recommendations, and ethical or environmental choices. In recent years, several studies have claimed that high consumption of animal protein may be associated with an increased risk of mortality, particularly from cancer and cardiovascular disease, while plant protein may have protective effects.

This controversy is fueled by several factors. On the one hand, methodological variability in studies (cohorts, follow-up duration, dietary assessment methods, statistical adjustments) makes comparisons difficult. On the other hand, certain biological hypotheses, such as the role of IGF-1 (Insulin-like Growth Factor-1) in the link between protein and cancer, remain debated. Variations in the populations studied (age, health status, overall dietary habits) further complicate interpretation. So what is the truth?

The study

To try to answer these questions, researchers used data from the NHANES III (National Health and Nutrition Examination Survey), collected between 1988 and 1994, which includes detailed information on diet, health status, and various biological parameters in American adults aged 19 and older. After exclusions (dietary data deemed unreliable, pregnancy or breastfeeding, ineligibility for follow-up), the final sample consisted of 15,937 participants (7,483 men and 8,454 women). Mortality data were obtained by matching with the National Death Index, covering the period up to December 31, 2006.

To estimate usual protein intake (total, animal, and plant), the authors used the multivariate Markov chain Monte Carlo (MCMC) method. This approach allows for the correction of measurement errors inherent in dietary surveys and the joint modeling of several variables (energy, protein, fat, carbohydrate intake, etc.), incorporating covariates such as age, sex, and ethnicity.

Animal protein included protein from meat, poultry, fish, dairy products, and eggs, while plant protein came from grains, legumes, nuts, seeds, and vegetables. Mixed foods were broken down according to the estimated proportion of protein from each source.

In addition to analyses of all-cause, cardiovascular, and cancer mortality according to protein intake, the authors also examined blood concentrations of IGF-1 (measured in 5,753 participants) and their possible association with mortality.

Results & analysis

With an average protein intake in this sample of 82g/day (of which approximately 57g was of animal origin and 25g of plant origin), the main results of this study show that there is no significant association between habitual consumption of animal and/or plant protein and all-cause mortality. Similarly, no significant link was found between animal and/or plant protein consumption and mortality from cardiovascular disease, regardless of the indicator used. Factors associated with higher cardiovascular mortality were advanced age, smoking, and physical inactivity, but not the type or amount of protein consumed.

With regard to cancer mortality, this analysis reveals that higher animal protein consumption is associated with a modest but significant reduction in the risk of cancer mortality. For each 10g/day increase in animal protein, the risk decreases by approximately 40%. This protective effect remains after adjustment for plant protein intake and other covariates. In contrast, plant protein intake is not associated with a reduced (or increased) risk of cancer.

Finally, circulating IGF-1 concentrations were not associated with mortality from any cause. Analyses by age group (under 65, 50–65, over 65) did not show any significant changes in this finding. This result contrasts with some hypotheses linking high IGF-1, animal protein, and increased cancer risk.

These results contradict some influential publications that reported an increased risk of mortality, particularly from cancer, among people aged 50 to 65 who consumed high amounts of animal protein. The discrepancy could be explained by methodological differences, particularly the larger sample size in this new study.

The fact that no negative association was found between animal protein consumption and all-cause and cardiovascular mortality, and that a modest protective effect appears to exist with regard to cancer mortality, raises questions about the relevance of generalized recommendations to reduce the proportion of animal protein in the diet in favor of plant protein alone. The authors suggest that if plant-rich diets are associated with better health profiles, this may be less due to the nature of the proteins themselves than to other beneficial compounds present in these foods (fiber, polyphenols, micronutrients), or to the concomitant substitution of less favorable foods.

The role of IGF-1, often presented as a mediator of the link between animal protein and cancer, appears less clear here. The data show no link between circulating IGF-1 and mortality, and suggest that the relationship may be more complex, potentially non-linear or dependent on the type of cancer. This calls for caution in the use of single biomarkers as a basis for nutritional recommendations.

Practical applications

These results call for a more nuanced approach to simplistic messages such as “less animal protein is better for health” or “more plant protein = guaranteed protection.” The lack of a negative association between animal protein and mortality, combined with a small protective effect for cancer mortality, suggests that the overall quality of the diet and the foods selected, the diversity of protein sources, and energy balance are likely to be more important than the animal or plant origin of the protein alone.

This does not mean that we should consume only animal protein, but rather that it can perfectly well be part of a balanced diet, alongside a variety of plant proteins. Choices can be guided by considerations of taste, tolerance, accessibility, and the environment, but current data do not justify, from a strictly health perspective, a drastic reduction for the entire population.

The emphasis should therefore be on maintaining adequate protein intake, particularly in older people, to preserve muscle mass and physical function, on the variety of protein sources to benefit from a full spectrum of amino acids and nutrients, and on not neglecting other aspects of nutrition (quality of fats, micronutrient density, fiber intake, limiting added sugars and ultra-processed foods, etc.).

Reference

Papanikolaou, Y., Phillips, S. M., & Fulgoni, V. L. (2025). Animal and plant protein usual intakes are not adversely associated with all-cause, cardiovascular disease–, or cancer-related mortality risk: An NHANES III analysis. Applied Physiology, Nutrition, and Metabolism, 50, 1–8.