A sweeping review of more than 350 studies has found that eating less protein may slow aging, improve metabolism, and in some cases extend lifespan — a conclusion that sits uneasily beside the current trend of fortifying everyday foods with added protein.

Dudley Lamming of the University of Wisconsin-Madison and a colleague examined hundreds of studies and identified several recurring biological patterns. Their analysis suggests that restricting protein intake can alter how cells sense nutrients, reduce cellular damage, and help the body regulate energy and blood sugar.

Lamming acknowledged that protein remains valuable for physically active people. "It's absolutely crystal clear that there are benefits of protein to muscle growth and exercise response of active individuals," he said. But most people, he noted, are not especially active and are "likely consuming more protein than they actually need, which probably has negative health consequences."

The review, as covered by ScienceDaily, does not prove that eating less protein lengthens human life. Even so, recent clinical trials have found that participants who ate less protein lost weight, reduced body fat, and improved fasting blood sugar — even when they consumed more total calories. How such benefits hold up over longer periods, though, remains untested.

US protein guidelines are climbing

The findings arrive at a moment when protein consumption in the United States is higher than ever. This year, US authorities updated their dietary guidelines to recommend 1.2 to 1.6 grams of protein per kilogram of body weight — roughly 0.5 to 0.7 grams per pound — nearly double the previous recommendation. Older adults in particular are being advised to eat more protein to preserve muscle strength.

For less active adults, official advice and the new review now point in different directions — a gap made more conspicuous by the spread of protein-fortified everyday foods, which can raise intake for people who are not deliberately seeking it.

Lamming's team does not fully reject that guidance. Age-related muscle loss can raise the risk of weakness and falls, and higher protein intake combined with exercise can help offset it. The crucial point, they argue, is that protein recommendations should be tailored to both age and activity level.

"We probably need to personalize protein recommendations based not just on age, but also on how physically active people are," Lamming said. The review also notes that pregnant women require more protein.

Three amino acids under scrutiny

The review highlights one mechanism in particular: fibroblast growth factor 21, or FGF21, a hormone that rises when protein intake falls. Elevated FGF21 can increase energy expenditure, stabilize blood sugar, and reduce inflammation. In mice, animals with higher FGF21 levels lived longer — especially males — though it remains unclear whether the same effect occurs in humans, a question only longer human trials can settle.

Total protein may not be the only variable. The review identifies three amino acids — methionine, isoleucine, and valine — that, in excess, can activate growth pathways tied to obesity, inflammation, and age-related disease. Two diets with the same protein total could therefore behave differently in the body depending on their amino acid makeup. That suggests the relationship between protein and aging is more complex than simply eating more or less of it.

Not everyone considers the evidence conclusive. As reported by IBTimes Australia via Ground News, scientists want larger and longer human trials before any changes are made to dietary advice. Until those results arrive, the review's practical significance rests on its authors' central argument: that protein needs are not one-size-fits-all, and that the right amount for a given person depends on age, activity level, and life stage rather than a single number for everyone.