Powerful new evidence suggests that following the Mediterranean diet while also cutting calories and increasing physical activity reduces the risk of Type 2 diabetes.
A large randomized trial in Spain found that older adults at risk of diabetes who followed that diet, reduced their caloric intake and exercised regularly were 31% less likely to develop the disease after six years, compared with those who just followed the Mediterranean diet. The diet emphasizes fresh fruits and vegetables, whole grains, nuts, legumes, olive oil and fish.
The findings build on results from an earlier, related trial, which found that participants who simply followed a Mediterranean diet were 30% less likely to develop diabetes than those who followed only a low-fat diet. (In that trial participants did not restrict calories, increase physical activity or experience weight loss.)
The study, published last week in The Annals of Internal Medicine, adds to a large body of research showing that dietary patterns, physical activity, and weight loss can reduce the risk of diabetes and other chronic diseases.
“It confirms a lot of what we know,” said Elizabeth Selvin, a professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health.
Diet and activity are some of the most important risk factors for cardiovascular disease and diabetes,” said Selvin, but are hard to study. This type of large randomized trial of dietary and behavioral interventions, carried out over several years, is difficult but important to do, she added. That’s because randomized trials offer the strongest evidence that a given intervention, and not some other factor, is causing the difference in outcomes observed between two groups.
The role of diet, exercise, and weight loss in reducing diabetes risk was established in a landmark trial from the Diabetes Prevention Program in 2002. Patients who were randomly assigned to receive education, exercise at least 150 minutes a week, and follow a low-calorie, low-fat diet to reduce their weight by 7% saw a 58% reduction in their risk of diabetes compared with the placebo group.
Selvin’s research, published in August in Nature Medicine, found that a modified DASH diet rich in fruits, vegetables, and low-fat dairy products helped patients with diabetes reduce their average blood glucose level. They also increased the amount of time spent within the recommended range. Another study, published in August in Nature Medicine, found that the Mediterranean diet was linked to lower chances of Alzheimer’s disease among those at high genetic risk.
The Spanish trial followed nearly 5,000 adults ages 55-75 who were overweight or obese and had metabolic syndrome but no history of cardiovascular disease or diabetes at baseline. (Metabolic syndrome is a cluster of conditions — like high abdominal fat, high blood sugar, and high blood pressure — that increase one’s risk for developing diabetes and other chronic diseases.)
Those in the intervention group met with a dietitian regularly for six years and were counseled on how to follow the Mediterranean diet and reduce calories. They were also advised to adopt an exercise program of 45 minutes per day, six days a week, of brisk walking or an equivalent aerobic activity, plus additional strength and balance training two to three times per week. Those in the control group received only education on the Mediterranean diet, and they met with dietitians less frequently. All participants received olive oil, an expensive component of the diet.
The intervention group lost more than 7 pounds after six years, on average, and reduced waist circumference by 1.4 inches, on average, compared with just over 1 pound and 0.1 inch in the control group. The amount of weight lost in the intervention group represented 3.7% of body weight, less than doctors often think is needed to reduce the incidence of diabetes.
“The good news is that even a modest change impacted the risk,” said Miguel Ángel Martínez-González, a professor of public health at the University of Navarra and one of the investigators of the trial.
The 31% relative reduction in diabetes risk meant, essentially, that the measures in the intervention group would lead to approximately three fewer cases of diabetes per 100 people.
“We have no way of parsing out what was the key factor here,” said Dr. Tirissa J. Reid, an associate professor of medicine at Columbia University Irving Medical Center who was not involved in the trial. But it is well established that weight loss makes a difference in reducing diabetes risk and was very likely an important driver of the results, she added.
She said that long before Type 2 diabetes or prediabetes presents, patients commonly develop insulin resistance, a condition in which their body doesn’t respond as well to insulin. Physical activity and high-fiber diets like the Mediterranean diet — as well as weight loss — can help reduce that resistance.
The diet, exercise and weight loss could also reduce inflammation and oxidative stress, a process that damages cells, researchers said. Together, the benefits may lower diabetes risk.
“It’s like an orchestra,” said Dr. Jordi Salas Salvadó, a professor of nutrition at Universitat Rovira i Virgili in Spain and the senior author of the study. “One instrument sounds very good, but when several instruments are playing at the same time, the song is better.”
A notable component of the trial, said Nicole Patience, a registered dietitian at the Joslin Diabetes Center in Boston who was not involved, was the intensity of education and support.
Six years is “a long time to help people stay aligned with their intentions” and to make lasting behavior change, she said. Participants in the treatment group had regular and frequent contact with a dietitian, whereas the control group didn’t receive the same level of guidance. It’s unclear how much of a factor the support was, versus the dietary and activity intervention itself.
In the real world, replicating that level of contact could be difficult. And the Mediterranean diet may not be right for everyone.
Still, Patience said, this study shows that making small adjustments to a diet and adding exercise can make a big difference in long-term health.
This article originally appeared in The New York Times.
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