Protein is an essential part of a healthy diet, and for older adults, it’s especially important. Recently, researchers suggested that restricting dietary protein can promote metabolic health, healthspan, and lifespan, but nutrition experts disagree.
According to a review paper published in Cell Press Blue, a protein-restricted diet can improve longevity through several biological mechanisms. However, experts argue that the evidence is not convincing, and following this advice could put older adults, people with a sedentary lifestyle, and those on GLP-1 weight loss medications at serious health risk.
Stuart Phillips, a professor of kinesiology and skeletal muscle health expert at McMaster University, described the study as “a beautiful mouse story, sold as human advice” in a social media post. He noted that in people over 65, low protein is linked to worse outcomes, including more frailty, more falls, and higher mortality.
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Phillips told STAT that the evidence from animal research cannot 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.
The latest Dietary Guidelines for Americans recommend 1.2 to 1.6 grams of protein per kilogram of body weight. Donald Layman, a professor emeritus of nutritional sciences at the University of Illinois Urbana-Champaign, noted that the majority of Americans are meeting this higher range.
Layman’s observation is significant.
The Recommended Dietary Allowance recommends 0.8 grams of protein per kilogram of body weight, but experts say that older adults may need more protein than this.
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Stacy Pelekhaty, a registered dietitian and senior clinical nutrition specialist at the University of Maryland Medical Center, finds that most of her patients start focusing on longevity in the middle of life, when they may have higher protein needs due to chronic injuries or illness.
As humans age, the body’s ability to synthesize protein slows down alongside metabolism, creating an increased demand for dietary protein to maintain lean muscle. William Evans, a protein and aging researcher and adjunct professor of human nutrition at the University of California, Berkeley, said that he is “very skeptical” of the proposed benefits of a protein-restricted diet for older adults.
Phillips noted that a mixture of minimally processed plant and animal foods is very different from simply adding protein bars, powders, and “protein-fortified” snack foods to an otherwise poor diet. Protein goals should be individualized based on a person’s age, health status, muscle mass, kidney function, activity level, and overall goals.