Eating less protein could slow aging: major review of 350+ studies

Researchers at the University of Wisconsin-Madison, funded by the National Institute on Aging, reviewed more than 350 studies on protein restriction, amino acid restriction, and aging. The review found that lowering protein intake improved metabolism, reduced inflammation, and reduced cellular damage across multiple model organisms. Flies and rodents lived longer on protein-restricted diets even when their overall calorie intake did not decline. In human trials, participants who reduced protein lost body fat and improved fasting blood sugar, sometimes while consuming more total calories. The review identifies the amino acids methionine, isoleucine, and valine as particularly influential: excessive intake of these may activate growth pathways (notably mTOR) that accelerate aging. The hormone FGF21 emerged as a key mediator: it rises when protein intake falls, increasing energy expenditure and improving glucose regulation. Mice with elevated FGF21 lived longer, with stronger effects in males. The authors caution that protein needs are not uniform: athletes, pregnant women, and some older adults may benefit from higher intake. Updated US dietary guidance now recommends 1.2 to 1.6 grams per kilogram of body weight, nearly double previous recommendations.

Protein restriction may improve health and promote longevity through effects on metabolic function, nutrient signaling, and cellular damage, but guidance should be personalized by age and activity level.