THE ARISING · Longevity & Healthspan
Review Suggests Eating Less Protein May Slow Aging
Protein is being added to cereal, coffee and bottled water, and older adults are routinely urged to eat more of it, yet a new review argues that the evidence for "more is better" is far less settled than the shelf space suggests.
The paper, published in Cell Press Blue in 2026, is a review written by Knopf and Lamming. It draws on work in yeast, flies, rodents and people. Its central argument is that lower-protein diets promote metabolic health, healthspan and lifespan across diverse organisms.
The starting point is a gap between advice and data. The official Recommended Dietary Allowance for protein is 0.8 grams per kilogram of body weight, for nonpregnant adults. Intakes of 1.0–1.2 grams per kilogram are routinely recommended for people over 65 to prevent sarcopenia, the age-related loss of muscle, and frailty. The review reports that the most recent Dietary Guidelines for America suggest 1.2–1.6 grams per kilogram. According to a 2025 report cited in the review, 61 percent of American consumers increased their protein intake in 2024, up from 48 percent in 2019.
The authors set against this a body of evidence pointing the other way. In rodents, low-protein, high-carbohydrate diets extend lifespan and improve metabolic health. Protein restriction also increases the lifespan of yeast and flies. In rodents, it raises energy expenditure and cuts fat even though the animals eat more, and it still works when started late in life, at 18 to 20 months of age in mice.
Human data are mixed. Observational studies cited in the review link high-protein diets to a greater risk of diabetes, cancer and death, including death from cardiovascular events. An analysis of US national survey data found higher protein consumption tracked with higher mortality and more age-related disease. A 2023 UK study found that higher protein intake was positively associated with sarcopenia in older twins, which cuts against the usual advice.
Randomised trials point to metabolic effects of eating less protein. In a 2016 trial from the authors' group, people on a low-protein diet for 43 days had lower body weight, less fat mass and lower fasting blood glucose despite eating more calories. A five-week intervention in lean men improved insulin sensitivity and raised energy expenditure. In patients with metabolic syndrome, 27 days of protein restriction reduced fat, improved insulin sensitivity and lowered glucose, lipids and inflammation. Conversely, a high-protein, low-carbohydrate diet was less effective than a moderate-protein diet at lowering blood glucose and promoting prediabetes remission.
The review points to a hormone, fibroblast growth factor 21 (FGF21), as a central player. Protein restriction robustly raises FGF21 in mice, rats and humans. In mice, the hormone drives much of the response: animals engineered to make extra FGF21 lived about 30 percent longer in males and about 40 percent longer in females. Mice lacking the gene did not live longer on a low-protein diet. These are mouse findings; the lifespan question has not been answered in people.
The authors also describe two cellular nutrient-sensing pathways, GCN2 and mTOR. Low amino acid levels activate GCN2 and inhibit mTORC1, a master sensor of nutrients. In mouse knockout models, the benefits of protein restriction were lost without that mTORC1 inhibition.
Not all protein is equal in this account. Restricting just three amino acids, methionine, isoleucine and valine, recapitulates many of the benefits of protein restriction, according to the paper. That makes the amino acid makeup of the diet, not only the total amount, a key factor in aging.
On who should care, the evidence is not uniform. The paper acknowledges the case for higher protein in older adults, especially paired with resistance exercise, to combat muscle loss and frailty. In coverage by ScienceDaily, corresponding author Dudley Lamming said: "It's absolutely crystal clear that there are benefits of protein to muscle growth and exercise response of active individuals. But because most people are relatively sedentary, many people are likely consuming more protein than they actually need, which probably has negative health consequences."
Next to watch are longer human trials that measure muscle function alongside metabolic health. This review does not establish that eating less protein slows aging or extends life in people.