Eating Less Protein Could Slow Aging, Review of 350 Studies Suggests, but Scientists Warn Evidence Is Limited

A major scientific review of more than 350 studies is drawing renewed attention for its suggestion that eating less protein, not more, could slow aging and possibly extend lifespan. The finding challenges the high-protein trend that has swept supermarket shelves and fitness culture.

The review, by researchers at the University of Wisconsin-Madison, was published July 31 in the Cell Press journal Cell Press Blue. It found evidence that reducing protein intake may improve metabolism, reduce inflammation and cellular damage, and activate biological pathways linked to healthier aging.

"Despite widespread recommendations for higher protein intake during aging, increasing evidence suggests that dietary protein restriction (PR) promotes metabolic health, healthspan, and lifespan across diverse organisms," authors Bailey A. Knopf and Dudley W. Lamming wrote.

Earlier studies found that mice, rats, flies and fish fed less protein consistently lived longer and healthier lives, even when they did not eat fewer calories overall. In some human studies cited in the review, cutting protein improved blood sugar control and led to weight loss, even when participants ate more calories.

"These studies show that the amount of protein sedentary people are eating today may have negative health consequences, at least at the population level," Lamming said.

The authors identified several "hallmarks" of protein restriction, including improved metabolic health, fewer aging cells, better mitochondrial function and changes in how cells sense nutrients.

One key factor is a hormone called FGF21. Its levels rise when people eat less protein. The hormone has been linked to greater energy expenditure, better blood sugar control and lower inflammation. In preclinical research, mice with higher FGF21 levels lived longer than normal mice.

The review also found that total protein may not tell the whole story. Restricting specific amino acids, the building blocks of protein, particularly methionine, isoleucine and valine, produced many of the same benefits in animal studies as cutting protein overall.

The researchers argue that protein advice should be personalized based on physical activity. Active people and those building muscle may need more protein. Sedentary adults may benefit from eating closer to the recommended daily allowance of 0.8 grams per kilogram of body weight. The review suggests that simply meeting that level, without going over it, may be enough to improve health outcomes.

Independent scientists have urged caution. Most of the evidence comes from studies in rodents, insects and yeast rather than people. Paul Greenhaff, a professor of muscle metabolism at the University of Nottingham, said the review did not address the central question of whether protein restriction improves healthy aging and longevity in humans.

Writing in The Conversation, other researchers noted that the review was designed to understand the biology of aging, not to tell people how much protein to eat. They also noted that benefits seen in human studies could reflect eating less animal protein or a generally healthier diet.

Lamming and other aging researchers say people should not adopt very low-protein diets. Older adults in particular need enough protein to maintain muscle mass and strength, which helps prevent frailty and falls.

The review comes amid booming demand for high-protein products, from protein bars and shakes to fortified yogurts and snacks. Many of these are marketed to consumers who already eat more protein than they need.

The researchers say more long-term human trials are needed to determine the ideal protein intake for healthy aging.