Protein restriction can alter metabolism and slow down aging

Experts have put forward the following idea: the benefits of protein for muscle growth and adaptation to physical activity are undeniable. However, since most people lead a sedentary lifestyle, they are likely to consume more protein than they actually need, and this can have negative consequences for health.

Restricting protein partially mimics the effect of reducing dietary calorie intake. It has been known for many decades that reducing the number of calories consumed can extend life in various organisms and reduce the risk of age‑related diseases, including cancer. However, most people find it difficult to stick to a low‑calorie diet. Studies have shown that reducing the protein component of the diet can extend the lifespan of flies and rodents, even without reducing the total calorie intake. Recent clinical trials in humans have also demonstrated that reducing protein intake helps reduce weight and body fat volume, and improves fasting blood sugar levels, even in cases where participants consumed more calories overall.

However, the picture is not clear‑cut. A number of studies show that increased protein intake combined with regular physical activity can contribute to weight loss and prevent age‑related loss of muscle mass in older adults. It was precisely these data that prompted U.S. regulatory bodies to adjust dietary recommendations this year, raising the recommended protein intake to 1.2–1.6 grams per kilogram of body weight (0.5–0.7 grams per pound), almost doubling the previous values.

To make sense of the conflicting data, scientists analyzed decades of scientific research on the relationship between protein restriction and aging. Based on more than 350 publications, the team identified stable mechanisms that may explain how low‑protein diets improve health and promote longevity.

The review focuses particularly on the hormone FGF21 (fibroblast growth factor 21), the level of which increases when protein intake is reduced. FGF21 is capable of increasing the body’s energy expenditure, improving blood sugar control, and reducing inflammation. Experiments on mice showed that animals with higher FGF21 levels lived longer, and the positive effect was more pronounced in males. In humans, a decrease in the proportion of protein in the diet also leads to an increase in FGF21 levels.

Furthermore, the review highlights specific amino acids (the building blocks of protein) that largely determine these effects. We are talking about methionine, isoleucine, and valine. An excess of these amino acids can trigger biological processes that stimulate growth, and these, in turn, increase the risks of developing obesity, inflammatory conditions, and other age‑related diseases.

The level of physical activity also plays an important role. It is noted that athletes often consume large amounts of protein and do not experience metabolic disorders. It is likely that regular exercise helps the body use protein to build strong and healthy muscles, thereby protecting against the negative effects of excess protein in the diet.

According to the team, modern recommendations for protein intake should be personalized: they should take into account not only a person’s age but also their level of physical activity. While certain groups, such as pregnant women or some older adults, may indeed need an increased amount of protein, for most sedentary adults, protein‑enriched foods may not provide the health benefits that consumers expect.