An 83-year-old doctor and triathlete transformed his health in his 40s. He shares his 4 key diet principles.

• Dr. Joseph Maroon is an 83-year-old practicing neurosurgeon who competes in triathlons.
• Maroon uses four key diet principles to boost his health and longevity.

An 83-year-old doctor and triathlete who transformed his health in his 40s shared the diet principles he believes have helped him to live a long, healthy life.

Dr. Joseph Maroon, a neurosurgeon at the University of Pittsburgh Medical Center and panelist at the recent Global Aging Consortium, told Business Insider he struggled to climb a flight of stairs at age 40.

"I was out of shape, living on fast food and not exercising," he wrote on his website.

That year, his father died and his physical and mental health reached rock bottom. But after a friend suggested he try running to ease his depression, he started making gradual lifestyle changes, taking up more exercise and eating better.

By age 53, Maroon had signed up for his first Ironman Triathlon, and has since completed eight in total. Last year, Maroon came second in his age category for the 2022 National Senior Games triathlon.

Maroon previously shared how he stays fit with BI, and explained his diet principles below.

Follow a Mediterranean-style diet

Maroon said he follows the Mediterranean diet, which has been named the best way to eat by US News & World Report for seven years in a row.

It's not a "diet" in the way you might think, but more a way of eating that centers around healthy choices rather than restriction.

It's mostly plant-based, focusing on whole foods, including fruits and vegetables, whole grains, beans and legumes, and healthy fats such as olive oil. It includes some fatty fish, and red meat on occasion.

The diet has been linked to a multitude of health benefits, including a lower risk of heart disease, cancer, and Alzheimer's disease.

Avoid ultra-processed food

Ultra-processed foods are made using techniques that are difficult to recreate at home and may include additives including salts, sugars, and saturated fats, according to the NOVA scale, which categorizes foods by how processed they are.

An easy way to tell if something is ultra-processed is if it doesn't look like its ingredients — such as protein bars or hot dogs.

UPFs have been linked to an increased risk of illnesses, including cancer, dementia, and cardiovascular disease.

Avoid trans fatty acids

Trans fats can increase levels of "bad" LDL cholesterol in the blood while decreasing levels of "good" HDL cholesterol, which can increase the risk of heart disease and stroke, Dana Ellis Hunnes, a senior dietitian at UCLA Medical Center, previously told BI.

Artificial trans fats are made when vegetable oil is hydrogenated. They were commonly found in packaged, ultra-processed foods until the Food and Drugs Administration declared trans fats unsafe to eat in 2015. The FDA gave food manufacturers three years to remove trans fats from their products, so most foods no longer contain them.

However, foods can still legally contain under 0.5 grams of trans fats, registered dietitian Kristin Gillespie, previously told BI, so it can be worth watching out for them. They typically appear in ingredient lists as "partially hydrogenated" oil in foods such as margarine, pre-made pie crust, non-dairy coffee creamer, and packaged baked goods.

Eat less sugar

The healthiest diet involves "avoiding a whole lot of things that people like to eat," Maroon said, including sugar.

Dr. Heidi Tissenbaum, a professor in molecular, cell, and cancer biology at the University of Massachusetts Medical School, previously told BI that in her research, removing added sugar from the diet of roundworms, which are used to model human healthspan, was linked to increased longevity. It's thought this is because when the body metabolizes sugar, it produces byproducts that are associated with an increased risk of diabetes, cardiovascular disease, chronic kidney disease, and Alzheimer's disease.

It's also important to keep blood sugar levels stable to prevent wearing out the mechanism the pancreas uses to regulate spikes, which can increase the risk of developing type 2 diabetes, she said.

Avoiding ultra-processed foods, which tend to be high in added sugar, can help with this, as can eating more fiber-filled whole foods which help to regulate blood sugar levels.