Olive oil key to healthy diet?

People eating the so-called Mediterranean diet may be protected against weight gain – however much they eat, researchers say today.

The findings – from a major trial in Spain – suggest people should not be "afraid" of the healthy fats in the diet, arising from fish, olives and nuts, the researchers say.

The study in The Lancet Diabetes & Endocrinology is the latest in the increasingly heated debate about the role of fat and carbohydrates in weight gain and the development of disease.

In the UK obesity experts divided after one body, the National Obesity Forum, said carbohydrates were chiefly the cause of unhealthy diets – and criticised the use of low-fat foods.

In the latest study, Spanish researchers studied nearly 7,500 people in a randomised control trial.

Participants were assigned by dieticians to a Mediterranean diet rich in olive oil with unrestricted calories. A second group had a similar diet rich in nuts while a third group attempted a low-fat diet.

After five years all groups showed average weight losses but increased waist circumference.

The greatest weight loss was experienced by those in the high olive oil group, losing an average of 0.88 kg. This compared with 0.6 for the low-fat group and 0.4 kg for the nuts group.

Researcher Dr Ramon Estruch, of the University of Barcelona, said: “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.

“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 to 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."

He added: "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."

Effect of a high-fat Mediterranean diet on bodyweight and waist circumference: a prespecified secondary outcomes analysis of the PREDIMED randomised controlled trial. The Lancet Diabetes & Endocrinology 7 June 2016 [abstract]