The healthy fats--primarily olive oil and nuts--that are the backbone of the Mediterranean diet are unlikely to cause weight gain, HealthDay News reports of research from the University of Barcelona in Spain. It has long been thought that if you want to lose or maintain weight, you should follow a low-fat diet. That guideline may have just been turned on its head.

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What is a Mediterranean diet? Just as the name implies, it is characterized by the traditional cooking style of the countries bordering the Mediterranean Sea. Every meal is centered on plant-based foods, including fruits, vegetables, whole grains, beans, legumes, nuts, herbs and spices. Olive oil is used in place of all other fats. Fish, poultry, eggs, cheese and yogurt can be consumed in moderate amounts, while red meat and sweets are eaten only occasionally. Red wine, in moderation, is optional.

The study: Led by Dr. Ramon Estruch, the team followed more than 7,400 men and women in Spain, all of whom were between the ages of 55 and 80 and had either type 2 diabetes or a high heart risk. Fully 90 percent were either overweight or obese.

Each participant was placed on one of three eating plans:
1. unrestricted-calorie Mediterranean diet rich in olive oil
2. unrestricted-calorie Mediterranean diet rich in nuts
3. low-fat diet meant to avoid all dietary fat

The results after five years:

• The total fat intake fell from 40 percent to 37 percent in the low-fat diet group, while total fat increased from 40 percent to 42 percent in both Mediterranean diet groups. In addition, the percentage of proteins and carbohydrates decreased in both Mediterranean diet groups.

• Participants in all three groups lost some weight. On average the olive oil group lost almost 2 pounds, the low-fat group lost 1.3 pounds and the nut group lost 0.9 pounds.

• Waist circumference did increase slightly in all three groups, though less so in those on the healthy fat diets.

"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," Estruch explained. "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."

But do note this: Not all fats are created equal. Such fats as butter, processed meat, sweetened beverages, desserts and fast-food are not healthy.

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