Plant- and fish-based diets tied to healthier aging, study finds

Plant-based diets, with moderate fish and low in ultra-processed items, may support healthier aging, concludes new study

Fish may be brain food, but it turns out it could also be a key part of aging well. A new study led by researchers from Harvard T.H. Chan School of Public Health, the University of Copenhagen and the University of Montreal found that people who follow diets rich in plant-based foods –while including moderate amounts of healthy animal-based options like fish – are more likely to reach age 70 free of major chronic diseases, with their cognitive, physical and mental health intact.

It’s one of the first studies to connect mid-life dietary patterns with the full package of healthy aging, offering fresh insight into how what we eat now shapes the way we live later.

“Studies have previously investigated dietary patterns in the context of specific diseases or how long people live,” said co-corresponding author Frank Hu, Fredrick J. Stare Professor of Nutrition and Epidemiology and chair of the Department of Nutrition at Harvard Chan School. “Ours takes a multifaceted view, asking, how does diet impact people’s ability to live independently and enjoy a good quality of life as they age?”

The study, published in Nature Medicine, tracked over 105,000 adults between ages 39 and 69 for 30 years, drawing data from the long-running Nurses’ Health Study and Health Professionals Follow-Up Study. Participants regularly filled out food questionnaires, which researchers used to score how closely their diets aligned with eight recognized healthy eating patterns – like the Mediterranean diet, DASH and plant-based plans. These diets all emphasized whole foods like fruits, vegetables, whole grains, nuts and healthy fats, with some allowing modest amounts of fish and dairy.

The researchers also assessed participants’ intake of ultra-processed foods, which are industrially manufactured, often containing artificial ingredients, added sugars, sodium and unhealthy fats. In the end, just under 10 percent of participants aged healthfully, and those who stuck with any of the healthy diet patterns were more likely to reach 70 with their minds and bodies in good working order.

Can omega-3 fatty acids from fish eggs improve recovery and aging? Scientists aim to find out.

Among the eight diets studied, the Alternative Healthy Eating Index (AHEI) came out on top. This diet prioritizes fruits, vegetables, whole grains, nuts, legumes and healthy fats, while cutting back on red and processed meats, sugary drinks, sodium, and refined grains. Designed to help prevent chronic diseases, the AHEI was strongly linked to healthy aging: participants with the highest AHEI scores were 86 percent more likely to age well by 70 – and more than twice as likely to do so by 75 – compared to those with the lowest scores.

Another standout was the Planetary Health Diet Index (PHDI), which supports personal health and considers the planet – favoring plant-based foods and limiting animal-based ones to reduce environmental impact.

Higher intake of ultra-processed foods, especially processed meat and sugary and diet beverages, was associated with lower chances of healthy aging.

“Since staying active and independent is a priority for both individuals and public health, research on healthy aging is essential,” said co-corresponding author Marta Guasch-Ferré, associate professor in the Department of Public Health at the University of Copenhagen and adjunct associate professor of nutrition at Harvard Chan School. “Our findings suggest that dietary patterns rich in plant-based foods, with moderate inclusion of healthy animal-based foods, may promote overall healthy aging and help shape future dietary guidelines.”

The researchers acknowledged a key limitation: the study population consisted entirely of health professionals, a group that may not reflect the broader public. To better understand how these findings apply across different communities, the team emphasized the need to replicate the study in more diverse populations, especially those with varying socioeconomic backgrounds and ancestral origins.

“Our findings also show that there is no one-size-fits-all diet,” said lead author Anne-Julie Tessier, assistant professor in the Department of Nutrition at the University of Montreal, researcher at the Montreal Heart Institute, and visiting scientist at Harvard Chan School. “Healthy diets can be adapted to fit individual needs and preferences.”

Read the full study.