Friday, July 29, 2016

Does a High-Fat Mediterranean Diet Lead to Weight Gain?


Good evidence exists that the Mediterranean diet is associated with salutary outcomes, including results from the Prevención con Dieta Mediterránea (PREDIMED) study.[1] This study was a randomized trial of the Mediterranean diet vs a control condition of advice to reduce dietary fat alone among patients at elevated risk for cardiovascular events. The main study outcome was the incidence of major cardiovascular events, and the trial was stopped after a median follow-up period of 4.8 years because of a preponderance of positive results.

Compared with the control group, the hazard ratio for cardiovascular events among the Mediterranean diet group supplemented with extra-virgin olive oil was 0.70 (95% confidence interval [CI], 0.54-0.92), and the respective hazard ratio for participants randomly assigned to the Mediterranean diet supplemented with nuts was 0.72 (95% CI, 0.54-0.96). The Mediterranean diet appeared effective for these outcomes regardless of sex, age, and the presence of diabetes.

Nonetheless, concerns remain about the effects of the Mediterranean diet on obesity and central adiposity, despite previous research suggesting that the diet can be effective for weight loss. The current study by Estruch and colleagues revisits the PREDIMED cohort to investigate how the prescribed Mediterranean diet, which was not associated with a limitation on calories nor a recommendation for physical activity, compared with the control diet in the outcomes of body weight and waist circumference.


Following a Mediterranean diet that is not calorie restricted and is high in healthy fats from olive oil or nuts does not cause weight gain at 5 years compared with a low-fat diet, according to results from the Spanish PREDIMED randomized controlled trial.

"These results have practical implications, because the fear of weight gain from high-fat foods need no longer be an obstacle to adherence to a dietary pattern such as the Mediterranean diet, which is known to provide much clinical and metabolic benefit," write Ramon Estruch, MD, PhD, from CIBER OBN-University, Barcelona, Spain, and colleagues.

"They are also relevant for public health, because they lend support to not restricting intake of healthy fats in advice for bodyweight maintenance and overall cardiometabolic health, as acknowledged by the Dietary Guidelines for Americans 2015 Advisory Committee," they add.

The study was published online June 6 in Lancet Diabetes & Endocrinology.[2]

The study is the first randomized trial to evaluate the long-term effects of an unrestricted-calorie Mediterranean diet on weight and waist circumference.

Much evidence has linked a Mediterranean-style diet high in vegetable fats such as nuts and olive oil to decreased risks for all-cause mortality, cardiovascular disease, and cancer.

For the past 40 years, however, standard dietary advice for preventing or treating obesity has called for calorie restriction and increased physical activity, with a persistent belief that high fat intake promotes weight gain. Such recommendations, however, have not necessarily taken into account the different types of fat. Nonetheless, certain scientific societies -- including the World Health Organization[3] -- continue to advise limiting fat in the diet.

The idea that all dietary fat is unhealthy has led many US adults to curb their fat consumption, often at the expense of eating empty calories from processed foods high in sugar, salt, and carbohydrates. The demonizing of all fat, though, has failed to stem the tide of the diabetes and obesity epidemic.

The PREDIMED randomized controlled trial took place in primary care centers connected to 11 hospitals in Spain between 2003 and 2010. It included 4282 women 60 to 80 years old and 3165 men 55 to 80 years old with type 2 diabetes or 3 or more cardiovascular risk factors. All patients were asymptomatic, and more than 90% were overweight or obese at baseline. They had a mean age of 67 years; 97% were of white European ethnicity.

Researchers randomly assigned participants to an unrestricted-calorie Mediterranean diet with extra-virgin olive oil (n=2543), an unrestricted-calorie Mediterranean diet with nuts (n=2454), or a low-fat control diet (n=2450). Trained dieticians gave dietary advice to all 3 groups. Participants were not advised to restrict calories or increase physical activity.

Participants received free polyphenol-rich extra-virgin olive oil and nuts (walnuts, almonds, or hazelnuts). Results showed good adherence in the olive oil and nut groups, based on self-reported questionnaires, and blood and urine samples in a random subgroup.

Five-year results showed that total fat increased in the 2 Mediterranean diet groups. Both Mediterranean diet groups actually had a slight increase in fat consumption -- from 40% to 41.8% in the olive oil group and 40.4% to 42.2% in the nut group (P <.0001 for all) -- while their consumption of protein and carbohydrate decreased (P <.0001).

All 3 groups lost a small amount of weight. At 5 years, the olive oil group lost the most weight (0.88 kg), followed by the low-fat control group (0.60 kg), and then the nut group (0.40 kg). Multivariable analyses adjusted for 12 potential confounders showed that the difference in weight change at 5 years was significant only for the olive oil group vs the control group (P =.044).

Likewise, all 3 groups had a slight increase in average waist circumference, but the increase was smaller for the Mediterranean diet groups (low-fat control group, 1.2 cm; olive oil group, 0.85 cm; nut group, 0.37 cm). Multivariable analyses adjusted for 12 potential confounders showed that the difference in change in weight circumference at 5 years was significant for both the olive oil and nut groups vs the control group (P =.048 and P =.006, respectively).

In a linked comment,[4] Dariush Mozaffarian, MD, DrPH, from the Friedman School of Nutrition Science and Policy at Tufts University, Boston, Massachusetts, writes that these results provide "further robust evidence that liberally adding healthy foods to the diet, including high-fat choices such as nuts and extra-virgin olive oil, does not increase weight gain."

"These important findings should be heralded around the world," he asserts, while calling for the revision of dietary guidelines.

Decades of dietary advice have ignored food quality and the different effects of specific fatty acids, he pointed out.

By emphasizing calorie and fat restriction, such advice has produced "paradoxical warnings and caveats about eating healthy, high-fat foods" and fostered the proliferation of low-fat foods -- often high in sugar and carbohydrates -- in the US diet.

"[M]odern scientific evidence supports an emphasis on eating more calories from fruits, nuts, vegetables, beans, fish, yoghurt, phenolic-rich vegetable oils, and minimally processed whole grains; and fewer calories from highly processed foods rich in starch, sugar, salt, or trans-fat. We ignore this evidence -- including these results from the PREDIMED trial -- at our own peril," he concludes.

  • The PREDIMED trial demonstrated that a Mediterranean diet supplemented with extra-virgin olive oil or nuts reduced the risk for incident cardiovascular events among high-risk patients, regardless of age, sex, or the presence of diabetes.
  • The current study by Estruch and colleagues demonstrates that the Mediterranean diet was not associated with weight gain compared with a low-fat diet in older adults at high cardiovascular disease risk. The Mediterranean diet provided a slight benefit in waist circumference compared with the control diet.
  • Implications for the Healthcare Team: The Mediterranean diet is not only effective in reducing the risk for cardiovascular disease, but the current study suggests that it may reduce central adiposity as well. Moreover, it is one the more palatable healthy diets for many patients. The healthcare team should focus on how to add elements of the Mediterranean diet among at-risk patients.

Veronica Hackethal, MD

You can find older posts regarding ASEAN politics and economics news at SBC blog, and older posts regarding health and healthcare at IIMS blog. I thank you.

No comments:

Post a Comment