According to an article published in the scientific journal The Lancet Diabetes and Endocrinology, the Predimed study has reached the conclusion that ''Following a Mediterranean diet unrestricted in calories and rich in extra virgin olive oil or nuts does not tend to lead to significant weight gain in comparison with a low-fat diet.''
The study was carried out with the participation of 7,447 patients in Spanish hospitals. It showed that a typical Mediterranean diet ''had little effect on body weight or waist size when compared to people that are on a low-fat diet.''
What is more, scientific tests suggest that the total fat content of a food is not a reliable measure of how healthy it is. In fact, they add weight to the argument that the emphasis should be on eating more calories from fruit, nuts, vegetables, legumes, fish, yoghurt, whole-grain cereals and vegetable oils such as extra virgin olive oil. In contrast, we should consume fewer calories from processed foods rich in starch, sugar, salt and trans fats. Moreover, fats obtained from olive oil and nuts tend to be healthier than animal fats.
The study took place during the period 2003-2010 and all 7,447 participants were aged 55 to 80 and had a high risk of developing cardiovascular disease or type two diabetes. More than 90% were overweight or obese. The participants were organised into three groups. The first contained those that had a Mediterranean diet rich in olive oil and without calorie restrictions. The second diet group was similar but rich in nuts instead of olive oil. The third group was on a low-fat diet and had been advised to eat as little fat as possible.
After five years, the total fat intake per person had fallen in the low-fat diet group and had risen slightly in the other two groups. Meanwhile, the percentage of total energy consumed in proteins and carbohydrates increased in both Mediterranean diet groups. In these groups patients had on average increased their consumption of vegetables, legumes, fruit and fish and reduced that of meat, sweet foods and dairy products.
On average, patients in all three groups lost some weight, though the greatest weight loss occurred in the olive oil-rich Mediterranean diet group (0.88 kg compared to 0.6 kg in the low-fat diet group and 0.4 kg in the nut-rich diet group). In addition, there was a small increase in waist size in all three groups on average. The largest increase was observed in the low-fat diet group, 1.2 cm compared to 0.85 cm in the olive oil group and 0.37cm in the nut group.
The experiment demonstrates that following a Mediterranean diet rich in extra virgin olive oil or nuts ''had little effect on body weight or on waist size in comparison with the low-fat diet.''