In a 30-year study, researchers found that a certain diet was associated with healthy aging, defined as reaching the age of 70 without any major chronic health conditions, an intact memory, strong mental health, and the physical ability to move freely and climb stairs. Of the over 105,000 people studied, just one in ten were considered healthy agers—and they all had one thing in common: a diet rich in plant-based foods, low in highly processed foods, with a moderate intake of animal-based products. 

In the study, published last month in the journal Nature Medicine, researchers tracked how closely participants followed a slew of healthy diets. While adhering to any of the diets, including the Mediterranean and Planetary Health diets, increased the chances of healthy aging, the Alternative Healthy Eating Index (AHEI) was the most influential in improving people’s odds of maintaining strong mental and physical health at age 70. 

Those who adhered most strictly to the AHEI diet had an 86% higher chance of living to 70 without major chronic conditions compared to those who adhered to the diet the least. People who were the most loyal to the AHEI diet also had a 2.24 times greater chance of living healthfully at age 75 compared to those in the lowest quartile of adherence to the diet. This is especially relevant as 80% of older adults have more than one chronic condition, which increases the risk of early mortality.

Read more from Fortune

“Our findings suggest that dietary patterns rich in plant-based foods, with moderate inclusion of healthy animal-based foods, may enhance overall healthy aging, guiding future dietary guidelines,” the researchers conclude. “The AHEI was also the most strongly associated with maintaining intact physical function and mental health among individual healthy aging domains.”

What is the AHEI diet?

The AHEI diet, developed by Harvard scientists, was created to lower the risk of chronic conditions and emphasizes fruits, vegetables, whole grains, nuts, and legumes. The diet limits intake of animal products and discourages highly processed and sweetened foods, such as juice. 

Previous research has shown the benefits of plant-based diets rich in whole foods, such as fruits, vegetables, and legumes. The residents of the world’s blue zones, where people reportedly live the longest, are celebrated for eating a minimally processed diet. The “three sisters,” or food staples, of the blue zone, Nicoya, Costa Rica, for example, are squash, corn, and beans. 

The study used data from the Nurses’ Health Study and the Health Professionals Follow-up Study to track individuals between the ages of 39 and 69 over a 30-year period. It contributes to research on how diet influences not only how long you live, but also how long you live in optimal health. 

For more on aging and nutrition: 

• The 4 foods that science says can help you live to 100
• This dietician warns of one major issue with American diets. Here are her 4 tips to fix it
• An essential predictor of happiness is often overlooked, according to a global study