A comprehensive review of over 350 research papers suggests that reducing protein intake could offer significant health benefits, including weight management, improved metabolism, and potentially a longer lifespan. The findings challenge the prevalent trend of high-protein diets often promoted for muscle building and weight loss.
The review, conducted by researchers at the University of Wisconsin-Madison and published in Cell Press Blue, highlights that while protein is essential for bodily functions like repairing tissues and building muscle, many individuals, especially those with sedentary lifestyles, may be consuming more than they need. This excess protein could lead to negative health consequences.
Scientists propose that low protein intake can increase levels of fibroblast growth factor 21 (FGF21), a hormone that may enhance the body's energy expenditure, improve blood sugar control, and reduce inflammation. Animal studies have shown that higher FGF21 levels are associated with increased longevity, particularly in male mice. This hormone can also be elevated in humans when protein intake is reduced.
Furthermore, the review points to specific amino acids, the building blocks of protein, that may promote growth processes when consumed in excess. These processes are linked to an increased risk of obesity, inflammation, and age-related diseases. Dudley Lamming, the study's corresponding author, stated that while active individuals benefit from protein for muscle development, sedentary people might experience negative health effects from consuming high amounts.
However, the review's authors and external experts caution that much of the evidence stems from animal studies, and findings may not directly translate to humans. Professor Paul Greenhaff of the University of Nottingham noted that rodents and insects are not entirely representative models for human aging.
Despite these caveats, the review suggests that protein-fortified foods and supplements may not offer the health benefits expected by many consumers, particularly for those who are not highly active. The UK, for example, has seen a significant increase in consumers seeking protein-rich foods, with 56% of consumers looking for such products, according to a 2024 study cited in the review. Current UK guidelines recommend 0.75g of protein per kilogram of body weight daily for healthy adults, equating to about 45g for a 60kg woman and 55g for a 75kg man. Some experts also warn that very high protein diets could strain kidneys, especially in individuals with pre-existing kidney conditions.
Lamming suggests that protein recommendations should be personalized, taking into account not only age but also an individual's physical activity level. While athletes often consume large amounts of protein without apparent metabolic issues, potentially due to their physical activity levels aiding muscle development, the average sedentary person may not experience similar benefits and could face health risks.