Details on the review

For the review, published in Cell Press Blue, researchers analyzed 350 studies of protein-restricted diets in both animals and people and found that mice, rats, flies, and fish that ate less protein consistently lived longer and healthier lives.

They also found that in some small human studies, people who ate a diet where they restricted their protein for several weeks lost weight and fat mass. They saw improvements in their fasting blood sugar, even though the people on these diets typically ate more calories.

While the studies involving animals sometimes placed the animals on diets that were especially low in protein, the lower protein diet in the human studies was typically within the range of the official recommended dietary allowance (RDA) of 0.8 grams of protein per kilogram of body weight, which is set by the Food and Nutrition Board of the National Academies of Sciences, Engineering, and Medicine.

Recent U.S. dietary guidelines recommend people consume 1.2 to 1.6 grams of protein per kilogram of body weight each day, which is up to twice the RDA.

According to the researchers, eating the RDA of protein and no more than that seemed to be sufficient to improve health outcomes in people. "Accumulating evidence challenges the idea that higher protein intake is beneficial," the researchers wrote.

According to Lamming, cell division can accelerate aging and disease. "One of the easiest ways to think about this is that every time you replicate a cell, you need to copy its DNA, and that process isn't perfect. There are always errors introduced," he said. "Every time a cell divides, it increases the chance of that cell getting cancer."

But when a person limits their protein consumption, the body may prioritize repairing and recycling cells rather than making new ones, which some scientists believe could help delay aging.

Lamming also noted a hormone called FGF21 could play a role.

"There's an increase in a hormone called FGF21 that promotes energy expenditure [when protein intake is reduced]," he said. "It essentially increases thermogenesis in your adipose tissue, so you don't just store fat, but actually burn it as fuel."

However, Lamming noted research on protein restriction has been small in scale and short-term and that more research is needed to understand how protein restriction could impact exercise and people of different ages and needs.

According to Phillips, evidence from animal research can't be directly translated to improved longevity in humans. "The authors acknowledge that the effect of protein restriction on human lifespan is unknown. That is the central limitation," he said.

Separately, William Evans, a protein and aging researcher and adjunct professor of human nutrition at the University of California, Berkeley, said that as humans get older, the body's ability to synthesize protein slows down alongside metabolism, which creates an increased demand for dietary protein in order to maintain lean muscle. For older adults, Evans said he's "very skeptical" of the proposed benefits of a protein-restricted diet.

Evans also cautioned against conflating maximal lifespan with a healthy lifespan. "Longevity doesn't necessarily mean better care for geriatric patients," he said, adding that it's important to consider questions like, "'How do we keep older adults out of nursing homes?' and 'How do we help them live a functional, independent life?'"