Study shows high-fat Mediterranean diet does not cause weight gain
Researchers found that people whose diets were high in olive oil and nuts lost more weight than those who ate a low-fat diet
Those in the study who ate a zero-calorie Mediterranean diet supplemented with extra virgin olive oil lost the most weight.
The Mediterranean diet, high in fat from olive oil and nuts, does not lead to weight gain, according to a large study.
The fear of fat is misplaced and guidelines restricting it in our diets are wrong, say the Spanish researchers, who observed more than 7,000 people, some eating 30g of nuts or 50ml of extra virgin olive oil a day, while others were placed on a standard low-fat diet. Their research, they say, should put healthy fats -- found in vegetables and fish -- back on the menu and change attitudes and the way we eat.
The release of fat and weight loss data from the respected Predimed randomized controlled trial follows excitement over a paper published by the UK's National Obesity Forum. The campaign document attacked Public Health England's dietary guidelines, claiming that eating saturated fats, including butter and meat, would allow people to lose weight. A scathing response from Public Health England said it was "irresponsible and misleading the public". Four members of the NOF resigned, saying they did not support the newspaper's publication.
However, the Mediterranean diet in the Predimed study does not contain red meat or butter, although it is high in fat. Participants ate fish, nuts, vegetables, fruit, and whole grains. "Many foods and beverages associated with long-term weight gain, such as fast foods, sweets and desserts, butter, red meat and processed meats, and sugar-sweetened beverages are not included," the authors write in the Lancet Diabetes and Endocrinology Journal.
The participants were randomly assigned to one of three groups. Some ate a zero calorie Mediterranean diet with added extra virgin olive oil (they received 1 liter per week for themselves and their family), while others ate a zero calorie Mediterranean diet with added nuts - they received 15g of walnuts, 7.5g of almonds and 7. 5g of hazelnuts, with an additional 1kg bag of mixed nuts every three months to meet the family's needs, the newspaper said. The third group was put on a low-fat diet and received small non-food gifts, such as a kitchen clock or spoons, every three months.
More than 90% of the participants between the ages of 55 and 80 were obese or overweight. The weight loss was not significant but was greatest in the Mediterranean diet group with olive oil - 0.88 kg compared to 0.60 kg for the low-fat diet. All groups increased their waist circumference, which occurs with age, but the smallest increase was seen in those eating a Mediterranean diet with added nuts (0.37 cm compared to 1.2 cm in the low-fat group).
The Barcelona-based researchers believe the findings should rehabilitate the Mediterranean diet high in healthy fats, which has known health benefits including reducing heart disease and cancer.
The belief that fat always makes you fat because it is high in calories led to the mass sale of low-fat and non-fat foods in supermarkets four decades ago. It had the unfortunate effect of contributing to the obesity epidemic as food manufacturers substituted sugar and other carbohydrates for fat in everything from yogurts to ready meals.
"More than 40 years of dietary policy advocates for low-fat diets, but we see little impact on the rise in obesity," said lead author Dr. Ramon Estruch from the Spanish Biomedical Research Center for Physiopathology of Obesity and Nutrition at the University of Barcelona, Spain.
"Our study shows that a Mediterranean diet high in plant-based fats such as olive oil and nuts had little effect on body weight or waist circumference compared to people on a low-fat diet. The Mediterranean diet has known health benefits and includes healthy fats such as vegetable oils, fish and nuts. Our findings certainly do not imply that an unrestricted diet high in unhealthy fats such as butter, processed meats, sweetened beverages, desserts, or fast foods is beneficial.”
Obesity is a global problem, putting people at risk for heart disease, cancer, stroke and diabetes. The standard weight-loss advice is a low-fat diet, the researchers say, while health panels, including the World Health Organization, recommend that fat should make up no more than 30% of our diet.
"Dietary guidelines should be revised to eliminate outdated, arbitrary limits on total fat intake," writes Prof. Dariush Mozaffarian of the Friedman School of Nutrition Science & Policy at Tufts University, Boston, USA, in a comment in the journal.
"Calorie-obsessed caveats and warnings about healthier, higher-fat alternatives like nuts, phenolic-rich vegetable oils, yogurt and maybe even cheese should also be dropped. We need to dispel the myth that lower-fat, lower-calorie products result in less weight gain.”
We should focus on the quality of our food, not the calorie content of restaurant menus, and it's paradoxical to ban whole milk but allow sugar-sweetened non-fat milk, he writes.
“The fat content of foods and diets is simply not a useful metric for assessing long-term harm or benefits. Energy density and total caloric content can be similarly misleading. Rather, modern scientific evidence supports an emphasis on consuming more calories from fruits, nuts, vegetables, beans, fish, yogurt, phenolic-rich vegetable oils, and minimally processed whole grains; and fewer calories from highly processed foods high in starches, sugars, salt, or trans fats. We ignore this evidence – including these results from the Predimed study – at our peril.”
Prof Simon Capewelll, vice president for policy at the Faculty of Public Health, said the study and commentary “provide clear nutritional messages; We need to promote a Mediterranean diet of olive oil and nuts and reduce our consumption of meat, animal fats, refined carbohydrates, junk food and sugary drinks.”