Low-Protein Diets: Can Cutting Back on Protein Extend Lifespan?
The U.S. Departments of Agriculture and Health and Human Services this month released updated Dietary Guidelines for Americans, significantly increasing the recommended daily protein intake for adults. The new guidelines suggest a range of 1.2 to 1.6 grams of protein per kilogram of body weight, nearly double the previous recommendation of 0.8 grams per kilogram.
The shift towards prioritizing protein comes as research continues to explore the complex relationship between protein consumption, longevity, and overall health. Although adequate protein is essential for building and repairing tissues, a growing body of scientific work suggests that restricting protein intake can extend lifespan in various organisms, from yeast to mice.
Researchers have found that mice fed a diet with only 6% of calories from protein lived longer, though not as long as those on a calorie-restricted diet (80% of normal calories), according to a recent study. Mice on the low-protein diet exhibited improved metabolic health, including lower blood sugar and insulin levels, and boosted levels of protective antioxidant enzymes. These benefits were most pronounced in middle-aged mice.
Stuart Phillips, a physiologist at McMaster University in Hamilton, Canada, describes protein restriction as a “lite” version of caloric restriction, a well-established longevity technique in lab animals. He suggests that studying protein restriction can provide insights into how bodies sense nutrients and respond to excess or shortage, potentially informing strategies for healthy aging. “There’s a lot to be learned from the principles of protein restriction about how we would manage aging, and aging well,” Phillips said.
Scientists are investigating the underlying biological mechanisms behind these effects. One theory, proposed by Clemence Blouet, a neuroendocrinologist at the University of Cambridge, likens the body to a car: driving at a slower pace conserves fuel and extends the vehicle’s lifespan. Similarly, a high-protein or high-calorie diet may accelerate aging processes, while restricting intake could promote cellular repair and reduce damage from free radicals.
Another perspective, offered by Christopher Morrison of the Pennington Biomedical Research Center, focuses on the hormone FGF21, produced by the liver. When protein intake is low, FGF21 signals the brain, triggering a cascade of responses that include increased protein intake and slowed growth. Mice engineered to lack FGF21 did not experience the life-extending benefits of a low-protein diet, highlighting the hormone’s crucial role in mediating the effects of protein restriction.
Stephen Simpson, a nutritional biologist at the University of Sydney, suggests that animals adopt different strategies depending on the availability of nutrients. When protein is abundant, they prioritize growth and reproduction, potentially sacrificing longevity. When protein is scarce, they activate protective mechanisms to survive until conditions improve. This “hunker down” approach, he argues, could explain the observed benefits of protein restriction.
The Sustainable Shrimp Partnership highlighted the new dietary guidelines, noting that a single serving of shrimp provides about 18 grams of complete lean protein, delivering all nine essential amino acids, omega-3 fatty acids, and essential vitamins and minerals. The organization suggests shrimp is a healthy protein choice for those seeking to meet the increased recommendations.
While animal studies offer promising insights, scientists caution against directly applying these findings to humans. Long-term studies on the effects of protein restriction in people are challenging to conduct. Epidemiological studies have yielded mixed results, with some suggesting a correlation between higher protein intake and increased risk of cardiovascular disease and type 2 diabetes, though these results may be skewed by saturated fat intake from animal protein. One study found that a low-protein diet correlated with a lower likelihood of death from cancer or any cause for people aged 50 to 65, but the pattern reversed for those over 65.
Researchers acknowledge that protein needs vary with age and that adhering to a protein-restricted diet long-term could be difficult, as protein is known to promote satiety. No scientists interviewed by Knowable Magazine reported currently restricting their own protein intake.