Scientists have long known that what we eat can affect how long and how well we live.
While many diets promise better health, researchers are now focusing on a different question: which eating pattern helps people stay healthy as they grow older?
A new study from the University of Southern California (USC) suggests that the answer may be a mostly plant-based diet that includes fish and carefully balanced amounts of protein.
The research, published in Cell Metabolism, combined animal experiments with data from more than 200,000 people. Together, the findings suggest that eating mostly plant foods while limiting protein—but still getting enough essential amino acids—may help reduce obesity, type 2 diabetes, frailty and other age-related health problems.
The scientists, led by Professor Valter Longo of the USC Leonard Davis School of Gerontology, have spent many years studying diets linked with healthy aging.
Their work has been inspired by traditional Mediterranean and Okinawan diets, two eating patterns followed by some of the world’s longest-living populations. These diets contain large amounts of vegetables, beans, whole grains and healthy fats, while including only modest amounts of fish and relatively little meat.
For the new study, researchers developed what they call a longevity diet with low protein but enough of an important amino acid called methionine. Methionine is found naturally in eggs, meat, dairy products and fish.
The body needs it to build proteins and support many normal functions, but scientists wanted to learn whether the amount of methionine matters for healthy aging.
The team tested four different diets in older mice. One group ate a standard diet, another ate a Western-style diet high in fat and sugar, a third followed a ketogenic diet, and the final group received the longevity diet with a carefully controlled amount of methionine.
The results were striking. Mice eating the longevity diet stayed healthier for longer, had less body fat, and showed fewer signs of frailty.
They also had healthier markers related to metabolism, including higher levels of hormones such as GLP-1, which helps regulate blood sugar and appetite. Surprisingly, these mice ate as much food as the other groups and sometimes even more, yet still lost fat while keeping their muscle mass.
The researchers then examined existing health and diet information from more than 200,000 people. They found that people who consumed the highest amounts of animal protein also consumed more methionine and were more likely to have obesity and about twice the rate of type 2 diabetes compared with people who ate little or no animal protein.
These patterns remained even though the higher-protein group often consumed fewer calories overall.
Professor Longo believes these findings suggest that the balance of amino acids may be just as important as the total amount of protein. Too little methionine increased frailty, while too much removed many of the diet’s benefits. This indicates that getting the right amount, rather than the highest amount, may be the key.
The findings are promising, but there are important limitations. Most of the strongest evidence came from mice, and animal studies do not always produce the same results in humans.
The human part of the research was observational, meaning it can identify links but cannot prove that the diet directly caused better health. Carefully controlled clinical trials in people will be needed before doctors can recommend this eating pattern as a treatment.
Overall, the study provides encouraging evidence that a mostly plant-based Mediterranean-style diet with moderate fish intake and carefully balanced protein may help support healthy aging. Future human trials will determine whether this approach can truly extend healthy lifespan.
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The study was published in Cell Metabolism.
Source: University of Southern California.
