Mediterranean diet does not lead to weight gain

The Mediterranean diet, with a high fat content from olive oil and nuts, does not cause people to gain weight, a major study has found.

Fear of fat is misplaced and guidelines that restrict it in our diets are wrong, say the Spanish researchers, who have followed more than 7,000 people, some eating 30g of nuts or 50ml of extra virgin olive oil a day while others were put on a standard low-fat diet. Their research, they say, should put healthy fats — from vegetables and fish — back on the menu, changing attitudes and the way we eat.

The Mediterranean diet in the Predimed study, however, though high in fats does not include red meat or butter. Participants ate fish, nuts, vegetables, fruits, and whole grains. “It does not include many foods and beverages that have been associated with long-term weight gain, such as fast foods, sweets and desserts, butter, red meat and processed meat, and sugar sweetened beverages,” write the authors in the Lancet Diabetes and Endocrinology journal.

Those who took part were randomly assigned to one of three groups. Some ate an unrestricted-calorie Mediterranean diet with added extra virgin olive oil (they were given one litre a week for themselves and their family), while others ate an unrestricted-calorie Mediterranean diet with added nuts — they got 15g of walnuts, 7.5g of almonds, and 7.5g of hazelnuts, with an additional 1kg sachet of mixed nuts every three months to account for family needs, says the paper. The third group were put on a low-fat diet and given small non-food gifts every three months, such as a kitchen clock or spoons.

More than 90 per cent of those who took part, aged between 55 and 80, were obese or overweight. Weight loss was not substantial, but was greatest in the Mediterranean diet with olive oil group — 0.88kg compared with 0.60kg on the low-fat diet. All the groups increased their waist measurement, which tends to happen as people age, but the smallest increase was among those eating a Mediterranean diet with added nuts (0.37cm compared with 1.2cm in the low-fat group).

The Barcelona-based researchers believe the results should rehabilitate the Mediterranean diet, high in healthy fats, which has known health benefits including reducing heart disease and cancer.

The belief that fat is always going to make people fat, because it is calorie-dense, led four decades ago to mass sales in supermarkets of low-fat and fat-free foods. It had the unfortunate effect of contributing to the obesity epidemic, as food manufacturers substituted sugar and other carbohydrates for fat in everything from yoghurts to ready meals.

“More than 40 years of nutritional policy has advocated for a low-fat diet but we’re seeing little impact on rising levels of obesity,” said lead author Dr Ramon Estruch from the Spanish Biomedical Research Centre in Physiopathology of Obesity and Nutrition at the University of Barcelona, Spain.

“Our study shows that a Mediterranean diet rich in vegetable fats such as olive oil and nuts had little effect on bodyweight or waist circumference compared with people on a low-fat diet. The Mediterranean diet has well-known health benefits and includes healthy fats such as vegetable oils, fish and nuts. Our findings certainly do not imply that unrestricted diets with high levels of unhealthy fats such as butter, processed meat, sweetened beverages, desserts or fast-foods are beneficial.”