It’s 2025 and it seems like we still can’t reach a consensus on which diet — vegan, keto, Mediterranean — is “the best.”
Experts say part of the problem is that what qualifies as “the best” or even “healthiest” depends on your personal goals. Are you looking to lose weight, build muscle, save the planet (and its animals) or reduce your risk of longterm chronic diseases?
If your focus is to be healthy well into your 70s, one Harvard-backed diet recently won the top prize in a longitudinal study published in the journal Nature Medicine.
Researchers analyzed the data of over 105,000 people aged 39-69 over the course of 30 years and found that those who strongly followed the Alternative Healthy Eating Index (AHEI) were 86% more likely to be healthy at 70 and more than twice as likely to be disease-free at the age of 75.
The AHEI was developed by Harvard T.H. Chan School of Public Health researchers as an alternative to the the Healthy Eating Index (HEI).
While they are similar in nature, the HEI was designed by the USDA to measure how well a diet stacks up to their dietary guidelines for Americans.
The AHEI, on the other hand, is more focused on preventing chronic diseases like heart disease, cancer and diabetes.
In comparison to the HEI, the AHEI places more emphasis on healthy fats, nuts, and legumes — and it allows for moderate alcohol consumption.
The diet also leans heavily on fruits, vegetables and whole grains while advocating for lower consumption of red and processed meats and sugar-sweetened beverages — both of which are bad for longterm heart health.
On its website, Harvard explicitly tells people who want to adhere to the AHEI to “focus on squeezing in extra servings of green leafy vegetables” — meaning ditch the potatoes and fries — and “avoid fruit juice, because drinking too much might actually increase your risk of diabetes.”
They also advocate for minimizing refined grains in favor of whole grains like brown rice and quinoa, getting at least a serving a day of plant-based protein, adding a weekly helping of fish, and swapping butter for olive oil.
“Studies have previously investigated dietary patterns in the context of specific diseases or how long people live,” study co-author Frank Hu, Chair of Nutrition at the Harvard T.H. Chan School of Public Health, said in a press release.
“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 found that 9.3% of its participants — 9,771 people — were in good cognitive and physical health by the time they were in their 70s.
“Since staying active and independent is a priority for both individuals and public health, research on healthy aging is essential,” co-author Marta Guasch-Ferré said.
“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.”
But while the AHEI diet may have been the winner, the researchers found that strong adherence to any of the 8 healthy diets they focused on was associated with aging well.
The runner-up was the Planetary Health Diet Index (PHDI), which is an eco-friendly version of the AHEI diet that is more plant-forward and encourages sustainable food choices.
“Our findings also show that there is no one-size-fits-all diet,” lead author Anne-Julie Tessier, assistant professor in the Department of Nutrition at the University of Montreal, said. “Healthy diets can be adapted to fit individual needs and preferences.”
