The study, which analyzed the health data of more than 100,000 people over the course of 30 years, is the first of its kind to examine how dietary patterns affect not only lifespan but also how well people age. The upshot: A diet emphasizing vegetables, fruits, healthy fats and some animal products such as fish and dairy over the long term was the most likely to make a difference in aging in good health.
Sticking to a balanced diet with a moderate amount of healthy animal protein, in fact, outperformed following a more plant-based diet, in terms of healthy aging. The researchers also found that eating more ultraprocessed foods was linked to worse physical and cognitive health in older age.
The study, published in Nature Medicine and led by researchers at Harvard University, the University of Copenhagen and the University of Montreal, adds to the growing body of research on human health spans—the number of years we live in good health—and the factors that can extend those years.
Though Americans are living longer, they spend less of their later years in good health. One reason is that medical advances have turned once-fatal conditions into chronic ones. Another is the rising prevalence of conditions such as obesity, diabetes and substance-use disorders.
“Staying active and independent is a priority from a public health standpoint, and for many of us,” says Anne-Julie Tessier, an assistant professor at the University of Montreal who led the study.
The dietary habits most closely linked to healthy aging, she added, likely work by reducing inflammation, improving metabolism and supporting gut health.
What is healthy aging?
The researchers defined healthy aging as reaching 70 in good cognitive, physical and mental health and without developing a major chronic disease such as cancer, diabetes or heart disease. Just under 10% of the people tracked over the 30-year period hit that milestone, they found.
To examine the connection to diet, the study’s authors looked at three decades’ worth of questionnaires that asked health professionals in midlife to recall and record, on average, what foods they ate and how often. They filled these out every four years. For example, how many shakes of salt did they add to food each day, and did they eat fresh or canned peaches?
The data come from two well-known, long-term research projects in the health world—the Nurses’ Health Study and the Health Professionals Follow-up Study, which were started at Harvard in the 1970s and 1980s and have been used to investigate a range of topics, from the effects of oral contraceptives to cigarette-smoking risks.
Researchers assigned scores to how closely people’s diets adhered to the crucial qualities of eight dietary patterns. They include various forms of the Mediterranean diet, which has been praised by doctors and scientists for everything from its brain-boosting to its anti-inflammatory benefits.
People who scored high in adhering to the so-called Alternative Healthy Eating Index, a plant-rich diet plus proteins such as dairy and fish, had an 86% higher chance of healthy aging than those whose diets scored lowest for that diet. Sticking to a plant-based diet with limited animal products also appeared to make a difference, but less so.
Diets high in trans fats, salt, sugary drinks, and red or processed meats—such as steak, ham and sausages—were linked to worse healthy-aging results.
More research needed
Other studies have looked at whether specific diets help people live longer. One published in 2023 found that sticking to similarly healthy diets was linked to a lower risk of premature death. Still, robust nutrition research is notoriously difficult to conduct. Many studies rely on participants recalling what they ate over weeks, months or years, which can be imprecise at best and inaccurate at worst.
This makes it impossible to know how much sugar or saturated fat people were actually eating, says Eric Brown, a research scientist in the National Institutes of Health’s Pediatric Translational Research Branch, who wasn’t involved with the study.
The questionnaires also don’t account for when participants eat. Some research suggests timing, such as whether people eat earlier or later in the day, can affect health markers including blood pressure, as well as how the body processes sugar. Other factors can skew results, too.
“If you eat a lot of vegetables, that could also be a marker for that you prepare a lot of home-cooked meals and that you eat fresh foods,” says Inge Lindseth, a registered dietitian and nutrition researcher in Oslo who wasn’t involved with the study.
The researchers tried to account for such issues by statistically controlling for factors such as participants’ body-mass index, how much they exercised and their financial standing.
Repeating the research in more diverse populations will help determine whether the results apply more broadly, says Tessier. Meanwhile, she adds: It is still important to remember diet isn’t a one-size-fits-all approach.
“This doesn’t mean ignoring personal preferences or cultural traditions,” she says. “Balance and enjoyment are definitely key.”
Write to Alex Janin at [email protected]