Protein-fortified foods are now common, appearing in products ranging from breakfast cereals and coffee to protein water. Yet a new review published on July 31 in Cell Press Blue suggests that consuming less protein may, for many people, offer greater health benefits and even help extend lifespan. Reviewing more than 350 studies on protein restriction and ageing, researchers found consistent evidence that lower protein intake may slow biological ageing by improving metabolism, altering how cells respond to nutrients, reducing cellular damage, and preserving healthy cell function.
“It’s absolutely crystal clear that there are benefits of protein to muscle growth and exercise response of active individuals,” says Dudley Lamming, the review’s corresponding author from the University of Wisconsin–Madison. “But because most people are relatively sedentary, many people are likely consuming more protein than they actually need, which probably has negative health consequences.” While calorie restriction has long been shown to extend lifespan and reduce age-related diseases in many species, maintaining a low-calorie diet is difficult. Protein restriction, however, may provide many of the same benefits without reducing total calorie intake.
Evidence from animal studies has shown that reducing protein intake can extend lifespan in flies and rodents, even when calorie consumption remains unchanged. Human clinical trials have also found that protein-restricted diets can reduce body weight, lower fat mass, and improve fasting blood sugar, despite participants often consuming more calories overall. Together, these findings suggest that the quality and quantity of protein consumed may influence health independently of total energy intake.
At the same time, research has demonstrated that higher protein intake, particularly when combined with regular exercise, can promote weight loss and help preserve muscle mass in older adults. These findings contributed to updated U.S. dietary recommendations encouraging adults to consume 1.2–1.6 grams of protein per kilogram of body weight each day—substantially higher than previous guidelines. Against this backdrop of increasing protein consumption, the researchers sought to understand better how protein restriction influences healthy ageing.
The review identifies several biological mechanisms that may explain these benefits. A key factor is fibroblast growth factor 21 (FGF21), a hormone that increases when protein intake is low. Higher FGF21 levels are associated with greater energy expenditure, improved blood sugar regulation, and reduced inflammation. In animal studies, elevated FGF21 has been linked to longer lifespan, with stronger effects observed in male mice. The review also highlights specific amino acids—including methionine, isoleucine, and valine—that may accelerate ageing-related processes when consumed in excess by stimulating pathways associated with obesity, inflammation, and chronic disease.
The authors emphasise that protein requirements should be individualised. Although athletes, pregnant women, and some older adults often benefit from higher protein intake, protein-fortified foods may provide little advantage for the average sedentary adult and could even have unintended health consequences. Lamming suggests that regular physical activity may protect athletes from the metabolic effects of a high-protein diet by directing protein towards muscle growth. “We probably need to personalise protein recommendations based not just on age, but also on how physically active people are,” he says.
More information: Bailey A. Knopf et al, The hallmarks of protein and amino acid restriction in aging and longevity, Cell Press Blue. DOI: 10.1016/j.cpblue.2026.100079
Journal information: Cell Press Blue Provided by Cell Press
