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Mediterranean Diet Helps Prevent Central Fat Distribution

In last week's Dr. Tim Says.... column I wrote about the effects of a Mediterranean-style diet on central adiposity - otherwise known as "belly fat." I recently ran across a study conducted in Spain that compares three different diets head-to-head on their effects on the distribution of belly fat, so I thought I'd share it with you (Diabetes Care 2007;30(7): 1717-1723).

The Spanish researchers recruited their volunteers from the children of their obese, type 2 diabetic patients. Eleven people qualified for the study, in that their Body Mass Index was over 25 (clinically overweight or obese), with a waist circumference of 102 cm or less in men and 88cm or less in women, and not on medications that might affect fat metabolism. Notably, all of the participants had an insulin sensitivity score that indicated that they were insulin resistant - a risk factor for developing type 2 diabetes.

At the start of the study the participants' percentage of body fat vs. lean body mass was measured using standard equipment, then their entire body was scanned to measure their body fat distribution (chest and abdomen vs. hip, thigh and leg).

The participants were then randomly assigned to one of three groups and underwent three dietary periods of 28 days each, meaning each participant followed each diet for 28 days, then switched to another for 28 days, then another. The diets in question were designed to maintain their existing body weight and were as follows:

• A low-fat, high-carbohydrate diet consisting of 15% protein, 65% carbohydrates and 20% fat (made up of 6% saturated fat, 8% monounsaturated fats, and 6% polyunsaturated fats)

• A high-fat, monounsaturated-fat rich diet consisting of 15% protein, 47% carbohydrates and 38% fat (which consisted of 9% saturated fat and 23% monounsaturated fats [75% of which was in the form of extra-virgin olive oil] and 6% polyunsaturated fats) (a Mediterranean-style diet)

• A high-saturated-fat diet consisting of 15% protein, 47% carbohydrates and 38% fat (23% saturated fat, 9% monounsaturated fat, and 6% polyunsaturated fat.

At the end of each 28-day period the volunteers underwent a glucose challenge to measure their insulin sensitivity, and their bodies were again scanned to look at body fat distribution.

Over the course of the study the Body Mass Indices and waist circumferences did not change - as you might expect, since their diets were designed to maintain their current weight. However, the high-carbohydrate diet caused more fat to accumulate in the chest and abdomen ("belly fat") than the legs. In fact, compared to the other two diets, the amount of fat in the legs actually decreased on a high-carb diet.

On the other hand, when following the high-fat, monounsatured fat diet, the participants experienced better insulin sensitivity than during the high-carb or high-saturated-fat diets.

Finally, insulin secretion actually fell during the high-saturated-fat diet when compared to either the low-fat, high-carb diet or the Mediterranean-style diet. Poor insulin secretion is another risk factor for diabetes.

What this means for you

This is a very small study but is very well designed in that the three diets were designed to maintain the volunteer's current weight. If the diets had been designed to help them lose weight, we would not be able to tell if any of the outcomes were due to losing weight or the composition of the diets. The significant point here is that versus a low-fat, high-carb diet, a Mediterranean-style diet higher in good monounsaturated fats seems to help you reduce your belly fat while protecting you from diabetes.

First posted: May 11, 2011