A University of Wisconsin–Madison review published in Cell Press Blue in August 2026 examined whether reducing protein or certain amino acids in the diet could affect biological processes linked to aging.

Animal studies suggest lower-protein diets—and restrictions on amino acids such as methionine, isoleucine or valine—can improve metabolic health and sometimes extend lifespan, even without cutting calories.

Short human trials have reported improvements in weight, body fat, fasting blood sugar and insulin sensitivity, but there is no evidence yet that protein restriction extends human lifespan or a clear target for amino-acid intake to promote longevity.

Possible explanations include increased FGF21, changes to the growth-related mTORC1 system that may encourage cellular recycling through autophagy, and fewer senescent cells; findings on mitochondrial effects were mixed.

But protein needs differ: higher intake may help with weight loss and muscle preservation, particularly alongside resistance exercise, while older adults may already get too little and face greater risks of muscle loss; pregnancy, injury recovery and physical activity can also raise protein needs.

Because most lifespan evidence comes from animals, where results can vary by sex and strain, the authors called for longer human studies that account for individual needs and measure frailty as well as metabolic health.