Type 2 diabetes prevented with adherence to Mediterranean diet and exercise, study finds

Each person in the clinical trial received a bottle of olive oil every month for free. MarianVejcik/iStockphoto/Getty Images via CNN Newsource

A combination of a lower-calorie Mediterranean diet, exercise and nutritional support kept overweight to severely obese people between the ages of 55 and 75 from progressing to type 2 diabetes, a new study found.

“Our study shows that modest, sustained changes in diet and lifestyle could prevent millions of cases of type 2 diabetes worldwide,” said coauthor Dr. Frank Hu, the Fredrick J. Stare Professor of Nutrition and Epidemiology and chair of the department of nutrition at Harvard T.H. Chan School of Public Health in Boston.

People who reduced their daily calories on the Mediterranean diet and engaged in moderate daily exercise — while also receiving professional weight loss support — had a 31% lower risk of developing type 2 diabetes than those who only followed the Mediterranean diet, according to the study published Monday in the journal Annals of Internal Medicine.

“I think this 31% reduction is probably a result of the combination of multiple components — improved diet quality, increased physical activity and modest weight loss,” Hu told CNN.

“The intervention group also had significant reduction in body fat percentage, and more important, a reduction in visceral adiposity (belly fat), and a significant improvement in body mass index,” he added. “The study showed that it’s not just weight loss, but also improvement in body composition may have contributed to the reduction in diabetes risk.”

At first glance, the study results were “boring,” said Christopher Gardner, Rehnborg Farquhar Professor of Medicine at Stanford University in California, who directs the Stanford Prevention Research Center’s Nutrition Studies Research Group. He was not involved in the study.

That’s because it’s well known that if people cut calories, eat a plant-forward diet with good fats and exercise they can prevent type 2 diabetes, Gardner said in an email.

But actuality, the study’s results are “staggeringly stunning,” he said. “I am accustomed in other similar studies seeing changes at 1 year that slowly diminish — most people are unsuccessful in making these changes, and if they do happen to make them, are unsuccessful at maintaining them.”

However, steady adherence over time to the lower calorie Mediterranean diet and daily physical activity allowed participants in the new study to keep their reduction in body weight and waist circumference, Gardner said.

“What is staggering is the 6 year adherence to these changes, with very little recidivism,” he said. “These participants made LASTING lifestyle changes. IT IS POSSIBLE.”

Long-term support helps adherence

The research is part of an ongoing eight-year randomized clinical trial in Spain called Predimed-Plus, in which 23 research centers tested how diet and exercise can reduce cardiovascular risk as well as other health conditions.

All 6,874 participants in the trial had body mass indexes between 27 (considered medically overweight) and 40 (considered seriously obese). While no one was diagnosed with type 2 diabetes at the start of the study, all participants had metabolic syndrome, defined as high blood pressure, high blood sugar, altered cholesterol and excess fat around the waist. Metabolic syndrome is a well-known risk factor for insulin resistance and later type 2 diabetes, as well as a buildup of plaque in arteries, which can lead to heart disease and stroke.

Half of the group was asked to follow a Mediterranean diet with a 30% reduction in calories — about 600 calories a day — and limit the intake of added sugar, refined breads and cereals, butter, cream, processed meats and sweetened drinks. About 35% to 40% of the daily calories were designed to come from healthy fats, 40% to 45% from healthy carbohydrates and 20% from protein.

“They were provided one liter of extra virgin olive oil for free each month to support their adherence to the Mediterranean diet, which emphasizes healthy fats,” Hu said.

“Overall during the six-year follow up, the amount of weight loss is not very big — only about 3% to 4% in the intervention group,” he said. “However, that shows even modest weight loss along with a healthy diet can have significant long term benefit on diabetes prevention.”

The intervention group was also asked to increase their aerobic exercise to 45 minutes daily, at least six days per week, along with exercises to improve strength, flexibility and balance, all of which are critical to aging well.

“You lose both lean muscle and fat mass when you reduce calories,” said Dr. David Katz in an email. Katz is a specialist in preventive and lifestyle medicine and the founder of the nonprofit True Health Initiative, a global coalition of experts dedicated to evidence-based lifestyle medicine.

“You protect lean muscle mass with exercise, especially if you add resistance training to build muscle,” said Katz, who was not involved in the study. “Generally, the ideal is to lose fat, retain muscle.”

In addition, the intervention group received help from trained dietitians three times a month during the first year, and monthly group sessions, individual sessions every three months, and two phone calls every three months for the remaining five years. The training included how to self-monitor and set goals.

“That was done intentionally,” Hu said. “You want the intervention group to improve their adherence to the diet, to increase their physical activity, and achieve more weight loss than the control group and the only way you can do that is through increased behavior intervention sessions.”

The remaining participants — who served as a control group — were also provided with monthly supplies of olive oil but only received general nutritional and exercise advice twice a year via group sessions. They had no calorie restriction, nor physical activity program, nor weight-loss goals.

What is the Mediterranean diet

Studies have found the award-winning Mediterranean diet can reduce the risk for diabetes, high cholesterol, dementia, memory loss, depression and breast cancer. The diet, which is more of an eating style than a restricted diet, has also been linked to stronger bones and a healthier heart.

The diet features simple, plant-based cooking, with the majority of each meal focused on fruits and vegetables, whole grains, beans and seeds, with a few nuts and a heavy emphasis on extra-virgin olive oil. Fats other than olive oil, such as butter, are consumed rarely, if at all, and sugar and refined foods are reserved for special occasions.

Red meat is used sparingly, usually only to flavor a dish. Eating healthy, oily fish, which are packed with omega-3 fatty acids, is encouraged, while eggs, dairy and poultry are eaten in much smaller portions than in the traditional Western diet.

Social interactions during meals and exercise are basic cornerstones of the Mediterranean style of eating. Lifestyle changes that are part of the diet include eating with friends and family, socializing over meals, mindfully eating favorite foods, as well as mindful movement and exercise.

By Sandee LaMotte, CNN