For sedentary adults, reducing protein intake, rather than restricting calories, might offer a more accessible route to a longer and healthier life, according to a recent scientific review.
While calorie restriction has long been associated with improved lifespan and reduced rates of age-related diseases, maintaining such diets can be challenging for many. A review of over 350 studies, published in Cell Press Blue, suggests that targeted protein restriction can yield similar metabolic benefits without the strict calorie limitations.
The findings indicate that lower protein consumption correlates with improved metabolism, altered nutrient signaling, decreased cellular damage, and enhanced cellular maintenance across the reviewed studies. A key factor in these benefits appears to be the metabolic hormone fibroblast growth factor 21 (FGF21). Protein restriction has been shown in animal studies to increase FGF21 levels, which can boost energy expenditure, lower inflammation, improve blood sugar control, and potentially extend lifespan.
Researchers identified three essential amino acids—methionine, isoleucine, and valine—that, under specific conditions, might be linked to aging-related biological pathways. For individuals who are not regularly exercising, elevated levels of these amino acids could lead to continuously active growth-related processes. Over time, this sustained stimulation may contribute to cellular damage, systemic inflammation, and weight gain.
"It’s absolutely crystal-clear that there are benefits of protein for muscle growth and exercise response of active individuals," stated Dudley Lamming, the paper's corresponding author and a researcher at 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."
The review acknowledges limitations, noting that as a scientific review rather than a new clinical trial, it identifies patterns across existing research but cannot definitively establish cause and effect in humans. Further long-term human studies are necessary to confirm if these metabolic benefits translate into increased lifespan.
The review emphasizes that protein requirements are not universal and should not be interpreted as a recommendation for inadequate consumption. Physically active individuals and athletes process protein differently; exercise directs amino acids towards muscle repair and building. High protein intake remains important for pregnant women and older adults who may experience age-related muscle loss.
For the general, largely inactive population, the findings suggest that public health guidelines could be refined to tailor protein targets based on an individual's age and activity level, moving away from broad recommendations.