Regular consumption of animal and plant protein is not associated with increased mortality

The debate over whether animal protein is “harmful” to longevity has been going on for a decade: Some studies have linked it to an increased risk of death, while others have not. A new paper in Applied Physiology, Nutrition, and Metabolism looks at the issue using large American data sets and the most rigorous method for assessing habitual (not one-time) consumption. The conclusion: neither total protein, nor animal, nor plant protein in normal amounts increases the risk of death from any cause, cardiovascular disease, or cancer. Moreover, people with a higher proportion of animal protein showed a modest but statistically significant decrease in the risk of death from cancer.

Background of the study

The debate about whether animal protein is “harmful” for longevity has been going on for years. Some large cohorts and meta-analyses reported increased mortality risks with high consumption of total/animal protein or the benefits of replacing it with plant protein, while others did not find convincing links or saw them only in certain subgroups and ages. Mechanistically, IGF-1 was most often pointed to as a potential link between protein, growth signals, and cancer risk, but the picture remained ambiguous according to population data. Against this background, a demand arose for more rigorous assessments with adjustments for measurement errors and habitual dietary patterns.

The key methodological problem of nutrition is the daily variability of diet: one or two 24-hour surveys poorly reflect usual consumption. Therefore, to interpret the relationships with outcomes (e.g., mortality), it is important to use specialized statistical approaches, such as the NCI (US National Cancer Institute) method, which separates intrapersonal variations from the true level of consumption and allows for more accurate comparison of risk groups. These methods have been validated on NHANES materials and are widely used in the analysis of nutrient patterns in large samples.

A separate practical issue is the source of protein. Animal and plant products come into the diet in different “components” (fats, minerals, degree of processing) and with different behavioral contexts (activity level, smoking, income), which is why observational associations are easily distorted by residual confounding. Distinguishing the influence of “how much protein” and “what it is made of” is possible only with careful statistics and careful adjustments. That is why the new work relies on a representative NHANES III database and assesses habitual consumption of animal and plant protein, comparing it with the risk of death from all causes, CVD and cancer, as well as with the level of IGF-1.

Finally, there are many public statements and press materials surrounding the topic, which reinforces the need for transparency. The authors of the article publish their results in a peer-reviewed journal and accompany them with open communication; in parallel, university press services emphasize the lack of signals of harm from normal levels of animal protein consumption and cautiously discuss possible protective effects. When reading such materials, it is important to rely primarily on the original source and the methodology of the analysis.

How it was conducted: data and statistics

The authors analyzed participants of the representative NHANES III survey (USA) - almost 16 thousand adults aged 19+, who were monitored using national mortality registries. The key point is the assessment of habitual protein consumption using the "gold standard" of statistics: the US National Cancer Institute (NCI) method and Bayesian MCMC modeling, which allows smoothing out daily fluctuations in diet and reducing errors in nutrition surveys. Then, the relationship between the proportion of animal/plant protein and mortality was assessed in risk models with adjustments for age, gender, and other factors.

What exactly was compared?

• Total protein, animal protein, vegetable protein - as a proportion and as grams per day.
• Three outcomes: mortality from all causes, from CVD, from cancer.
• Additionally: the role of IGF-1 (insulin-like growth factor-1), which is often “suspected” of being a mediator between the protein and the cancer risk.

Main results

No alarming signals were found: neither total, nor animal, nor plant protein at normal consumption levels were associated with an increased risk of death - either total, cardiovascular or cancer. In contrast, for cancer mortality, the group with higher animal protein consumption showed a moderate protective effect. In analyses where animal and plant protein were taken into account together, the picture remained the same: the contribution of plant protein to cancer risk was minimal, and that of animal protein was slightly protective.

What about IGF-1?

A common hypothesis is: “high animal protein → higher IGF-1 → higher mortality.” Here, no associations of IGF-1 with mortality were found for either total mortality, CVD mortality, or cancer mortality, either in the pooled sample or in age-specific analyses. This does not disprove the role of IGF-1 in all contexts, but it does not support the idea that normal population variations in IGF-1 explain long-term risks from protein.

What does this mean for the plate - a practical perspective

The work does not pass “sentences” on products, but rather clarifies the boundaries of a safe context:

• Focus on the overall "picture" of the diet, rather than demonizing the source of protein. Both animal (fish, dairy, eggs, white meat) and plant (legumes, soy, nuts) sources are appropriate in a healthy diet.
• Look at quality and processing: Whole foods and minimal processing are better than ultra-processed "protein" products.
• The ultimate risk is not a single nutrient: body weight, activity, blood pressure, lipids, and smoking cessation influence survival more than the tug-of-war between animal and plant protein.
  These findings are consistent with the authors' commentary: observational data, coupled with clinical trials, support the inclusion of both types of protein in moderate, habitual amounts.

How does this fit in with previous concerns?

In the past, “inconsistency” in results has often been attributed to methodology: some studies relied on single dietary surveys and did not account for variability, while others did not differentiate protein sources correctly. Here, a rigorous approach to assessing habitual intake is used, which reduces bias and improves interpretation. Against this background, the lack of a harmful association and the “hint” of cancer protection in animal protein seem plausible – although, of course, this is not a randomized intervention.

Important disclaimers and funding transparency

This is an observational analysis of NHANES: it does not prove causation or rule out possible residual confounding (lifestyle, social, and medical factors). The study is based on a US population; generalizability to other countries/dietary patterns requires caution. The press release notes that the project was funded by the National Cattlemen's Beef Association (through the Beef Checkoff), although the authors say the sponsor had no involvement in the design, analysis, or publication. It is appropriate to take this funding into account when reading the results, as is always the case when industry interests are involved.

Conclusion

In large, representative U.S. data, there is no evidence to suggest that typical, population-based amounts of animal or plant protein shorten life or increase the risk of dying from CVD or cancer. On the contrary, animal protein in this analysis was associated with a small reduction in cancer mortality, and the putative “bridge” via IGF-1 was not confirmed. The practical implication is less ideology and more balance: reasonable amounts of protein from different sources fit into a healthy diet if the rest of your lifestyle picture is working for your longevity.

Source: Papanikolaou Y., Phillips SM, Fulgoni VL 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 (online July 16, 2025), doi: 10.1139/apnm-2023-0594.