A large review by two researchers at the University of Wisconsin-Madison argues that eating less protein may slow the body’s aging. The paper, by molecular biologist Bailey Knopf and biomedical researcher Dudley Lamming, appears in the journal Cell Press Blue and draws on 361 scientific references1. Other reports describe it as a review of about 350 papers2 or “more than 350 studies”3.
The review is not brand new. It was first widely reported at the end of July and in early August 202632. It came back into the news this week with fresh coverage1 and with a critique, first published by Men’s Fitness on November 11, of what the headlines leave out4. This article looks at what the review rests on and how much of it applies to people.
What the review says
The authors frame their paper as a pushback on current advice. “Despite widespread recommendations for higher protein intake during aging, increasing evidence suggests that dietary protein restriction (PR) promotes metabolic health, healthspan, and lifespan across diverse organisms,” they write1. Healthspan means the years of life spent in good health.
Most of the striking results come from animals. Earlier studies found that eating less protein extended the lifespan of flies and rodents without cutting calories2. In the lab animals, lower-protein diets generally extended lifespan, and the animals ate more calories but stayed leaner because they burned more energy4. That suggests the effect is not simply a side effect of eating less overall4. Across many animal experiments, diets with less protein, but still enough to avoid deficiency, made animals leaner and better at controlling blood sugar, and in some experiments they lived longer5.
For people, the evidence is narrower. The researchers say several recent clinical trials found that eating less protein lowered weight and fat mass and improved fasting blood sugar, even though people on these diets tended to eat more calories2. Human studies have also linked cutting protein to less of the inflammation that is thought to speed up biological aging1.
How it might work, according to the authors
The review lists several possible explanations. Eating less protein may shift cell signaling toward upkeep rather than growth, reduce the build-up of senescent cells (worn-out cells that need clearing), and boost the energy production inside cells1.
One hormone gets particular attention: fibroblast growth factor 21, or FGF21. Its levels rise when protein intake is low2. FGF21 can raise the body’s energy use, improve blood sugar control and reduce inflammation2. It has been described as helping turn ordinary white fat cells into “beige” fat cells that burn energy3. In mice, animals with higher FGF21 levels lived longer than normal mice, with a bigger benefit in males than in females2. The researchers say eating less protein raises FGF21 in humans too2.
The review also points to particular amino acids, the building blocks of protein. Three stand out: methionine, isoleucine and valine2. All three are essential, meaning people must get them from food5. Studies suggest that too much of them can switch on growth processes linked to obesity, inflammation and other age-related diseases2. Lamming’s lab has previously reported that restricting isoleucine improved metabolic health and extended lifespan in mice5.
Another proposed link is mTOR, a signal inside cells that eating protein turns up. It pushes cells toward building and growth and away from autophagy, the cell’s cleanup and recycling process4.
What it does not show yet
The biggest gap is plain: the lifespan data come from mice, flies, worms and yeast, not humans4. Human studies so far have been short or observational, and there is no human lifespan data for protein restriction specifically4. Human studies can show whether lower-protein diets change weight, blood sugar or hormones over weeks or months, but they cannot yet show whether people live longer5.
The animal results are not uniform either. In one mouse study, restricting branched-chain amino acids (a group that includes isoleucine and valine) extended male lifespan by about 30 to 35% but shortened female lifespan by about 22%4. Lamming’s own group has found that mice respond differently depending on sex and genetic background5.
The type of review matters too. This is a narrative review, not a systematic review: the authors chose which studies to include and how to read them, rather than following set rules decided in advance4. That does not make it unreliable, but it is a weaker form of summary4.
Some human studies point the other way for certain groups. More protein can help preserve muscle, improve recovery after exercise and reduce the risk of frailty and sarcopenia, the loss of muscle with age5. Paired with exercise, more protein has been shown to help with weight loss and reduce age-related muscle loss in older adults2. Nutritionist Joseph Matthews of the University of Arkansas for Medical Sciences said that “what we need is a handful of high-quality human studies,” noting that applying the animal findings to people is still debated3.
Who is behind it
The review was written by Knopf and Lamming at the University of Wisconsin-Madison1. The paper’s declaration of interests states that Lamming has received funding from, and sits on the scientific advisory board of, Aeovian Pharmaceuticals, a company that is developing drugs that selectively block mTOR4. Since the review proposes mTOR as one reason protein restriction may help, that tie is relevant. The Men’s Fitness writer who flagged it said studies should not be dismissed over funding alone, but that the declaration should still be noted4.
Lamming himself does not argue for cutting protein across the board. “It’s absolutely crystal clear that there are benefits of protein to muscle growth and exercise response of active individuals,” he said. “But because most people are relatively sedentary, many people are likely consuming more protein than they actually need, which probably has negative health consequences.”1 He added that pregnant women and older adults may need more protein2.
How it fits the protein boom
The review lands while protein is being added to cereal, chips, coffee, snack bars and even water5, and to cookies and crackers4. According to a Ground News summary, current US dietary guidelines, updated this year under Health Secretary Robert F. Kennedy Jr., recommend nearly twice the previous protein target3.
Lamming said that for most inactive adults, protein-fortified food may not deliver the benefits people expect2. He also noted the other half of current advice: “Recent recommendations have encouraged people to eat more protein, but they’ve also encouraged people to exercise more,” he said. “We probably need to personalize protein recommendations based not just on age, but also on how physically active people are.”1
Where protein comes from may matter as much as how much. Lentils, salmon and an ultra-processed protein bar can carry similar protein but very different fiber, fats, salt and other compounds5. The mix of amino acids may matter as much as the total1. Kristin Kirkpatrick, a dietitian at the Cleveland Clinic, said she wants patients not to “blindly eat less protein” but to weigh the type of protein and their own needs based on age, activity level and health conditions5.
What to watch next
The authors call for a reassessment of how much protein people need by age and activity level, and say studies of groups of people that track protein’s effects on biological aging and metabolism could follow1. Critics set a higher bar: long-term human trials showing whether eating less protein leads to longer, healthier lives4. Until those exist, the trade-offs may look very different for an inactive 30-year-old than for an active 70-year-old4. Biohack will follow this thread as new human data appears.
