Less Protein May Slow Ageing, Boost Metabolism for Sedentary Adults

Protein has become a fixture of modern wellness culture. Walk into any grocery store and you'll find protein-fortified cereals, bars, waters, and coffee drinks lining the shelves—all marketed with the promise that more protein means better health. But a sweeping scientific review published in July challenges that assumption, at least for a large portion of the population.

Researchers at the University of Wisconsin-Madison examined more than 350 studies on protein restriction and aging, and their conclusion runs counter to the protein-maximization trend. For many adults, particularly those who are sedentary, eating less protein could actually improve metabolism, lower inflammation, protect cells from damage, and potentially extend lifespan. The findings suggest that biological aging itself may slow when protein intake drops, because cells respond differently to nutrient scarcity.

The mechanism at work involves a hormone called fibroblast growth factor 21, or FGF21. When protein consumption decreases, FGF21 levels rise. Higher FGF21 appears to increase how much energy the body burns, helps regulate blood sugar more effectively, and reduces inflammatory processes throughout the body. Animal studies have linked elevated FGF21 to longer lifespans, particularly in male mice. Human studies have shown the same pattern: lower protein intake correlates with higher FGF21 levels.

Dudley Lamming, the corresponding author of the review, put the finding plainly: most people are sedentary, and most people are probably eating more protein than they need. "It's absolutely crystal clear that there are benefits of protein to muscle growth and exercise response of active individuals," he said. "But because most people are relatively sedentary, many people are likely consuming more protein than they actually need, which probably has negative health consequences." The distinction matters. Exercise changes how the body processes protein, allowing it to build and repair muscle. Without that stimulus, excess protein appears to work against metabolic health.

The research also points to specific amino acids—methionine, isoleucine, and valine—as contributors to the aging process. Reducing intake of these compounds may lower biological processes linked to obesity and age-related disease. Earlier studies have shown that protein restriction can extend lifespan in flies and rodents without requiring people to cut overall calories, which is a significant finding given how difficult most people find calorie restriction. Several human trials have found that reducing protein intake lowered body weight, decreased fat mass, and improved fasting blood sugar levels, even when participants ate more calories overall.

But the researchers are careful not to suggest that everyone should eat less protein. Older adults who want to preserve muscle mass, pregnant women, and athletes all benefit from higher protein intake, particularly when combined with exercise. The updated U.S. dietary guidelines recommend 1.2 to 1.6 grams of protein per kilogram of body weight for many adults, a recommendation that reflects this nuance.

What the review ultimately argues for is personalization. Lamming noted that recent dietary advice has pushed both higher protein consumption and more exercise, but these recommendations don't account for the fact that different people have different needs. "We probably need to personalise protein recommendations based not just on age, but also on how physically active people are," he said. A sedentary office worker and a marathon runner have fundamentally different protein requirements, yet both receive the same generic guidance. The implication is clear: the era of one-size-fits-all nutrition advice may be ending, replaced by recommendations tailored to how people actually live.