Review of 350 Studies Finds Less Protein Slowed Aging in Animals

A review of more than 350 scientific papers concludes that eating less protein can slow biological aging in animals and may improve metabolic health in people, according to Cell Press. The paper appeared in the journal Cell Press Blue and was written by Bailey A. Knopf and Dudley W. Lamming, who is the corresponding author and works at the University of Wisconsin-Madison.

The authors say the evidence does not show that cutting protein extends human lifespan. It does suggest that protein intake influences several processes tied to aging and disease, which is a question of interest now that US dietary guidance has moved toward more protein.

What the review examined

This is a review, not a new experiment. Knopf and Lamming gathered decades of published work and looked for biological mechanisms that kept appearing across studies. They found several: lower protein intake appears to change metabolic function, alter how cells sense nutrients, limit cellular damage and help preserve the processes that keep cells working.

Much of the longevity evidence comes from animals. Experiments in flies and rodents showed that restricting protein lengthened lifespan even when total calories stayed the same. Researchers have long known that cutting calories extends life in many organisms, but sticking to a low-calorie diet is hard, which is why protein restriction has drawn interest as an alternative.

Human data are thinner. According to the review, several recent clinical trials found that people who ate less protein lost weight, reduced body fat and improved fasting blood sugar, even when they took in more calories overall. Fasting blood sugar is the level of glucose in the blood after a period without food, and doctors use it as a gauge of metabolic health.

A hormone and three amino acids

One mechanism involves fibroblast growth factor 21, or FGF21, a hormone that rises when dietary protein is scarce. It helps the body adapt to changes in nutrient supply, and higher levels can raise energy expenditure, support blood sugar regulation and reduce inflammation. In mice, animals with elevated FGF21 lived longer than those with normal levels. The effect was stronger in males, which suggests biological sex may shape the response.

Eating less protein also raises FGF21 in humans. Whether that rise brings the same longevity benefit seen in mice is not known.

The review also points to three amino acids, methionine, isoleucine and valine. Amino acids are the building blocks of proteins, and some also act as signals that switch on growth pathways. Growth signaling is needed for development and tissue repair, but the authors say excessive or prolonged activation may contribute to obesity, inflammation and other conditions that come with age. Limiting these specific amino acids might therefore account for some of the benefits seen with protein-restricted diets.

Why exercise changes the picture

Other research shows that more protein can aid weight loss and help older adults keep muscle, particularly alongside physical activity. Muscle loss raises the risk of weakness, reduced mobility and falls. Work like this helped prompt US authorities to revise their recommendations this year to 1.2-1.6 grams of protein per kilogram of body weight per day (0.5-0.7 grams per pound), nearly twice the earlier amount.

The authors stress that needs differ by person. Pregnant women need extra protein for fetal development, some older adults need more to maintain muscle, and people who exercise regularly use protein to repair and build tissue. Lamming noted that athletes often eat large amounts of protein without developing the metabolic diseases sometimes seen with protein-heavy diets, and exercise may change how the body handles those nutrients. For adults who sit most of the day, the authors say extra protein added to everyday foods may bring little benefit.

What this means

The review argues that protein guidance should reflect activity level as well as age. “We probably need to personalize protein recommendations,” Lamming said, adding that people were also urged to exercise more. He said many sedentary people probably eat more protein than they need, which “probably has negative health consequences.”

The picture is mixed by design. The paper credits protein with clear benefits for muscle growth and for active people, while pointing to animal and early human evidence that lower intake may help others. The open questions include whether the FGF21 response extends human life and how much the amino acid findings carry over from animals. The work was supported by the National Institute on Aging, the Wisconsin Partnership Program and the University of Wisconsin-Madison.

The paper is titled “The hallmarks of protein and amino acid restriction in aging and longevity” (Cell Press Blue, 2026, DOI 10.1016/j.cpblue.2026.100079).

Source: ScienceDaily