Mediterranean Diet Does Not Lead to Weight Gain or Central Adiposity: PREDIMED


People worried about bulging waist lines and packing on the pounds while following the Mediterranean diet—a diet rich in monounsaturated and polyunsaturated fats—can rest assured, according to the results of a new analysis of one of the landmark trials in this field.

Take Home. Mediterranean Diet Does Not Lead to Weight Gain or Central Adiposity: PREDIMED

In a prespecified secondary analysis of the PREDIMED study, investigators report that subjects randomly assigned to the Mediterranean diet supplemented with extra-virgin olive oil or mixed nuts did not gain any body weight or get wider through the midsection when compared with individuals assigned to a low-fat diet. In fact, long-term consumption of the Mediterranean diet with olive oil and nuts was associated with larger decreases in body weight and a reduction in waist circumference when compared with the control diet.

“At the beginning, we were worried about what would happen with a high-fat diet, such as the Mediterranean diet, because it contains of olive oil and nuts,” lead investigator Ramon Estruch, MD (University of Barcelona, Spain), told TCTMD. “We were worried about what would happen with body weight. To our surprise, following a traditional Mediterranean diet leads to weight loss and did not increase waist circumference. You don’t need to be afraid of gaining body weight if you follow the Mediterranean diet.”  

The analysis, which is published June 6, 2016, in the Lancet Diabetes & Endocrinology, supports nutritional policies that abandon the restriction of healthy fats for the prevention of weight gain, said Estruch.

Dariush Mozaffarian, MD (Tufts University, Boston, MA), told TCTMD that while there is a growing understanding about the benefits of monounsaturated and polyunsaturated fats, there remains a “phobia” about dietary fat, even healthy fats. As he writes in an accompanying editorial, the “focus on low-fat diets lives on.” In the United States, the American Heart Association (AHA) recommends consuming no more than 25% to 35% of total daily calories from fish, nuts, and vegetable oils, while the World Health Organization (WHO) suggests limiting total fat intake to 30% of total energy.

The 2015-2020 Dietary Guidelines for Americans, released by the US government earlier this year, emphasize a “healthy eating pattern” and do not make any recommendations regarding total fat intake. Mozaffarian noted these latest guidelines recognize monounsaturated and polyunsaturated fats as part of a healthy eating pattern, but he said there is still a concern about how many calories are packed into these healthy fats.

“If you look at the US dietary guidelines, if you listen to scientists speaking, we’ve replaced our fat obsession with calorie obsession,” Mozaffarian told TCTMD. “Very smart people and very smart guidelines are still really worried about and have a fear of fat-rich foods. I hear people say all the time, ‘Well, I know that nuts are good for you, and yes, we recommend nuts, but nuts have a lot of calories—so I really go out of my way to be sure people don’t eat a lot of nuts.’ The same caveats exist for healthy vegetable oils, and yet we don’t have those caveats for celery or carrots or other healthy things.”

While nuts and vegetable oils are more calorically dense than other foods, Mozaffarian said this has been conflated into a concern these foods lead to weight gain. However, as he points out in the editorial, “the fat content of foods and diets is simply a not a useful metric to judge long-term harms of benefits” and the “energy density and total caloric contents can be similarly misleading.”

Mediterranean Diet Previously Shown to Lower Risk of CVD

The PREDIMED study enrolled 7,447 men and women aged 55 to 80 years of age at high risk for cardiovascular events, randomizing them to one of three diets: a Mediterranean diet supplemented with extra-virgin olive oil, a Mediterranean diet supplemented with mixed nuts, and a control diet based on advice to reduce dietary fat.

In the two Mediterranean diets, participants received approximately one liter of extra-virgin olive oil per week or 30 grams of mix nuts daily (15 g of walnuts, 7.5 grams of hazelnuts, and 7.5 grams of almonds) to supplement a diet rich in fish, vegetables, fresh fruits, legumes, and wine with meals. In the control arm, low-fat dairy products, bread, rice, potatoes, pasta, fresh fruit, vegetables, and lean fish and seafood were recommended, while vegetable oils (including olive oil), nuts, fatty fish, and visible fats in meats and soups were discouraged.   

The main results of PREDIMED were published in 2013 in the New England Journal of Medicine and showed a 30% reduction in the risk of major cardiovascular events after 4.8 years among patients assigned to the Mediterranean diet supplemented with extra-virgin olive oil compared with the control diet. Similarly, those assigned to the Mediterranean diet with nuts had a 28% lower risk of major cardiovascular events compared with the low-fat diet. In 2006, the PREDIMED investigators had shown the Mediterranean diet (with olive oil and nuts) reduced blood pressure, plasma glucose levels, and C-reactive levels, and increased HDL cholesterol levels.  

To TCTMD, Estruch said 90% of the study population in PREDIMED was considered overweight or obese at the study onset so there had been a concern the intervention diets might result in further weight gain. As part of the study protocol, there was no caloric restriction or recommendations about physical activity.

At 5 years, individuals assigned to the Mediterranean diet plus extra-virgin olive oil and nuts lost 0.88 kg and 0.40 kg, respectively, while those assigned to low-fat control diet lost 0.60 kg. In a model that adjusted for multiple variables, including baseline body mass index and total energy intake, those assigned to the Mediterranean diet plus extra-virgin olive oil lost 0.43 kg more weight than did controls, a difference that was statistically significant. For those assigned to the Mediterranean diet supplemented with nuts, the multivariable-adjusted difference in body weight versus the control arm was not statistically significant.

Similar positive effects were observed with waist circumference. At 5 years, those assigned to the Mediterranean diet plus extra-virgin olive oil and nuts gained 0.85 cm and 0.37 cm across their midsections compared with a 1.20 cm increase in waist circumference in the control arm. Compared with those assigned to the low-fat diet, the multivariable-adjusted analysis showed significantly smaller increases in waist circumference at 5 years among those assigned to both Mediterranean diets.

Exceeding the AHA and WHO ‘Fat Caps’

To TCTMD, Mozaffarian said that with approximately 42% of energy derived from fat in the intervention diets, this amount exceeded the current cap set out by the AHA and WHO. “We need to get to the stage, both in science and in policy, where we recommend healthy foods period and recommend people avoid unhealthy foods period regardless of their fat content,” he said.

Mozaffarian believes the lack of weight gain observed with the high-fat Mediterranean diet is noteworthy because the trial was not designed with any emphasis on calorie restriction—individuals were free to eat how much they chose as long it fell within the framework of their dietary assignment. . “That’s why this particular finding is so important,” he said. “If you give people healthy fats, if you tell them to load up on these healthy fats and you don’t give them calorie restriction, they not only don’t gain weight, but they even look metabolically healthy in the end.”

Estruch echoed the sentiment, with investigators pointing out the results have practical implications, particularly if individuals are concerned about high-fat foods leading to weight gain. For individuals looking to lose weight, he recommends reducing portion sizes without altering the Mediterranean diet. In other words, to keep the same percentage of calories derived from fat in the diet but reduce caloric intake. 

While PREDIMED focused solely on diet, the ongoing PREDIMED-Plus study is another primary-prevention trial similar in design but with an added emphasis on caloric restriction and physical activity. With a plan to enroll 6,000 patients, patients will be randomized to the Mediterranean diet or the energy-restricted Mediterranean diet and the goal is to assess the effect of the diets on mortality and cardiovascular disease. Full results of PREDIMED-Plus are not expected until 2020.


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Michael O’Riordan is the Associate Managing Editor for TCTMD and a Senior Journalist. He completed his undergraduate degrees at Queen’s…

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Sources
  • Estruch R, Martinez-Gonzalez MA, Corella D, et al. Effect of a high-fat Mediterranean diet on bodyweight and waist circumference: a prespecified secondary outcomes analysis of the PREDIMED randomized controlled trial. Lancet Diabetes Endocrinol. 2016;Epub ahead of print.

  • Mozaffarian D. Food and weight gain: time to end our fear of fat. Lancet Diabetes Endocrinol. 2016;Epub ahead of print.

Disclosures
  • Estruch reports serving on the board and receiving lecture fees from the Research Foundation on Wine and Nutrition (FIVIN); serving on the boards of the Beer and Health Foundation and the European Foundation for Alcohol Research (ERAB); receiving lecture fees from Instituto Cerventes, Fundacion Dieta Mediterranea, Cerveceros de Espana, Lilly Laboratories, AstraZeneca, and Sanofi-Aventis; consultancy fees from KAO corporation, and receiving grant support through his institution from Novartis, Amgen, Bicentury, and Grand Fountaine.
  • Mozaffarian reports honoraria or consulting fees from Boston Heart Diagnostics, Haas Avocado Board, AstraZeneca, GOED, DSM, and Life Sciences Research Organization. He is named on a patent held by Harvard University for the use of trans-palmitoleic acid in the identification and treatment of metabolic disease. He reports chapter royalties from UpToDate and grant support from the National Heart, Lung, and Blood Institute and the National Institutes of Health.

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