A 78-year-old doctor says he's reversed his age by 20 years. Here are the 4 diet principles he follows to stay young.

• Dr. Michael Roizen is 78, but says his "biological age" is 57.6.
• He's the chief wellness officer at Cleveland Clinic, and takes his own advice on staying healthy.
• Dr. Roizen shared his diet principles with Business Insider, including sticking to the Mediterranean diet.

An expert in healthy aging who claims to have reversed his biological age by 20 years shared his diet principles with Business Insider.

Dr. Michael Roizen, an anesthesiologist and the chief wellness officer at Cleveland Clinic, is 78 years old. But he told BI his "biological age" is around 57.6, meaning that based on his risk of dying and or developing age-related chronic illness, his body appears to be decades younger. (It's important to note there is no consensus on the definition of biological age or how to measure it.)

Roizen used the same principles that he says have kept him young to develop a wellness institute at the Cleveland Clinic, giving employees financial incentives to implement healthy lifestyle changes. The program has saved Cleveland Clinic up to $200 million a year on the healthcare costs of 101,000 employee patients since 2008, according to Roizen, and informed their research initiatives on healthy aging.

Here are the diet principles Roizen follows.

Eat a Mediterranean diet

The Mediterranean diet primarily consists of whole foods such as fruits and vegetables, legumes, low-fat protein and dairy, and limits red meat, processed foods, and alcohol. It has been named the healthiest diet for seven years in a row by the US News & World Report, and research has linked it to better heart health, weight loss, and preventing cognitive decline.

Trout and salmon are his major sources of animal protein, which contain vitamin D and omega-3 fatty acids.

Eat a big meal at lunch

Roizen has his biggest meal at lunch and eats "very little" at dinner — usually just a salad. He can't sleep well after a heavy meal and then feels "much worse the next day."

A 2024 study by researchers at the University of Alagoas, Brazil, found that eating most of your calories at lunch could help to prevent and treat obesity, regardless of the quality of a participant's diet. Eating this way may align better with the body's natural rhythms, the team suggested.

Restricts calories five days a month

Roizen also follows the Longevity Diet developed by Valter Longo, a professor of gerontology and director of the University of Southern California Longevity Institute. He's been doing this for seven years. The diet involves restricting calories five days a month to mimic the effects of fasting.

Calories are dropped to 1,100 on the first day of the "fast," then to about 700 on days two to five. A 2024 study by Longo's team at USC found that participants on the fasting-mimicking diet had lower biological ages by an average of two and a half years after three months on the diet.

David Clancy, who studies the biology of aging at Lancaster University, UK, who wasn't involved in the study told BI at the time: "It's not unreasonable to think that, during ages 40 to 60 at least, this regime twice per year may add three to four years of healthy life, maybe more, in those with higher BMI, blood pressure, blood sugar, etc."

But he added the diet was "harsh" and working people may struggle to follow it. "Scheduling days four and five for weekend days would be sensible," he said.

Eat in an eight-hour window

Roizen intermittent fasts by eating between 11 a.m. and 7 p.m. each day.

He said that while the data on the impact of intermittent fasting on longevity is much less solid than the data on calorie-restricted fasting, but he said he likes how he feels.

"By the end of that 16-hour period, I'm feeling great and very energetic. I sleep much better and I seem to have much more energy as well," he said.

BI previously reported that research on the potential benefits of intermittent fasting aren't conclusive. One controversial study released earlier this year suggested that it may actually shorten person's lifespan, and others have suggested that it doesn't have benefit our health.