The low-fat-diet group total fat intake fell from 40% to 37% after 5 years. For both Mediterranean diet groups total fat intake rose from 40% to 42%.
People in all three groups lost some weight: an average of almost 0.88 kilograms per person in the olive oil group, 0.60 kg in the low-fat diet group, and 0.40 kg in the nut group, according to the researchers.
"Our study shows that a Mediterranean diet rich in vegetable 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 well-known health benefits and includes healthy fats, such as vegetable oils, fish and nuts", said study lead author Dr. Ramon Estruch, of the University of Barcelona in Spain. "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." he added. The study authors suggest that current health guidelines may be creating an unnecessary fear of these healthful fats.
"The fat content of foods and diets is simply not a useful metric to judge long-term harms or benefits. Energy density and total caloric contents can be similarly misleading. Rather, modern scientific evidence supports an emphasis on eating 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 rich in starch, sugar, salt, or trans-fat," Dr. Dariush Mozaffarian, professor in the School of Nutrition Science & Policy at Tufts University in Boston, wrote in an accompanying commentary.