The long-running debate over whether animal protein shortens lifespan has a new twist. A fresh reanalysis of a major U.S. dataset finds no clear link between typical amounts of animal or plant protein and higher death rates. The work also explores how a growth-related hormone factors into the picture.
What the large U.S. study examined and why it matters for protein intake
Researchers used data from NHANES III, a nationally representative survey that enrolled more than 15,000 adults between 1988 and 1994. Participants were at least 19 years old at baseline. Scientists tracked deaths over roughly 12 years to capture outcomes from all causes, including cancer and cardiovascular disease.
Because many lifestyle factors influence health, the analysis adjusted for age, sex, smoking, physical activity, and calories. These controls aimed to isolate the role of protein itself rather than other behaviors.
How intake and biological markers were measured
Estimating “usual” protein intake with modern statistics
Single-day food recalls can misrepresent long-term eating habits. To reduce that error, the team applied a multivariate Markov Chain Monte Carlo (MCMC) model.
- This approach estimates a person’s usual nutrient intake by adjusting for day-to-day variation.
- It also separates protein by source: animal (meat, dairy, eggs) versus plant (beans, nuts, grains).
Why IGF-1 was included
The investigators also measured blood levels of insulin-like growth factor 1 (IGF-1). Higher IGF-1 has been linked in some past studies to cancer and higher mortality. Including this hormone allowed researchers to test whether biology explained any diet–death connections.
What the new analysis found about protein and mortality
After accounting for diet variability and biological markers, the study found no evidence that higher intake of animal or plant protein raised the risk of early death.
Overall mortality, cancer death, and cardiovascular death were not higher among people who ate more protein. In fact, those with greater animal protein intake had a small reduction in cancer-related death risk.
Including IGF-1 in models did not change the results. The hormone did not emerge as a clear link between protein intake and mortality risk in this analysis.
Age-specific analyses also showed consistency. Younger adults, middle-aged groups, and older adults all showed no increased mortality tied to usual protein consumption.
The authors note that prior studies reporting stronger harms may reflect differences in methods. Older reports often relied on simpler intake estimates, which can misclassify long-term diet. The use of advanced modeling and balanced group sizes likely reduced some prior biases.
What nutrition experts say about daily protein targets
A medical writer and nutrition expert who was not involved in the research emphasized that people generally do not need to change their protein plans based on this study alone. Current guidance sets a minimum of about 0.8 grams per kilogram of body weight per day for most adults.
Experts point out that typical higher protein intakes still fall within the broader recommended range of 10–35% of total calories. They advise planning protein around personal goals like muscle maintenance, recovery, and satiety.
At the same time, specialists warn that not all protein sources are equal. Processed meats retain known links to cardiovascular disease and certain cancers. The study’s findings do not erase those established associations.
Who should consider eating more or different protein
Protein needs vary with life stage, activity, and health. A registered dietitian can help individualize targets. Groups who may benefit from higher or tailored protein include:
- Older adults — to maintain muscle mass and function.
- Athletes — for faster muscle repair and recovery.
- People recovering from illness or injury — to support immune response and tissue repair.
- Vegetarians and vegans — who should combine plant foods for a complete amino acid profile.
The Academy of Nutrition and Dietetics maintains a directory of credentialed dietitians for personalized guidance.
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