Dietary Modification Helps Patients at Risk for Metabolic Syndrome

September 14, 2010

By Robert Saunders

NEW YORK (Reuters Health) Sep 13 - A low-fat diet with a low glycemic index may increase insulin sensitivity in patients with impending metabolic syndrome. But replacing saturated fats with monounsaturated fats has less pronounced benefits, researchers say.

In an August 25th online paper in the American Journal of Clinical Nutrition, researchers in the UK report on the RISCK trial (an acronym for the five participating centers -- Reading, Imperial, Surrey, Cambridge, and Kings) involving 548 participants heading for metabolic syndrome. To enroll in the trial, patients had to score at least four out of a possible 12 on a scoring system that assigned points to components of the metabolic syndrome.

"Clearly achieving and maintaining a healthy weight is very important to reduce the risk of CVD, but we were interested in the additional effects of fat and carbohydrate, when energy intake is essentially left unchanged," said lead author Dr. Susan A. Jebb from MRC Human Nutrition Research in Cambridge in e-mail to Reuters Health.

The main aim of the trial was to determine the effect of two interventions on insulin sensitivity: replacing saturated fatty acids (SFAs) with monounsaturated fatty acids (MUFAs) or carbohydrates, and lowering the glycemic index (GI). The secondary outcomes were changes in cardiovascular risk factors.

Dr. Jebb and her colleagues randomly assigned the participants to either a reference group (for four weeks) or an intervention group (for 24 weeks). The groups -- and their unadjusted mean percentage changes in insulin sensitivity -- were as follows:

-- A high-MUFA and high GI diet: 2.1%

-- A high-MUFA and low GI diet: -3.5%

-- A low-fat and high GI diet: -8.6%

-- A low-fat and low GI diet: 9.9%

-- A high saturated fat and high GI diet (HS/HGI, the reference group): -4%

"This study did not support the hypothesis that isoenergetic replacement of saturated fatty acids with MUFAs or carbohydrates has a favorable effect on insulin sensitivity," the investigators report.

"In a post-hoc analysis we were able to clearly show a significant association between weight change and insulin sensitivity (even though the mean weight change was very small). This suggests that the effect of diet on body weight is more important than the changes in diet composition that we tested," Dr. Jebb noted.

However, there was an indication that the low fat/low GI diet did improve insulin sensitivity. Moreover, it improved triglyceride levels.

In fact, all the dietary interventions had a beneficial effect on lipids. Replacing saturated fats with MUFAs reduced total cholesterol and low-density lipoprotein cholesterol, and lowering the GI of the diet enhanced this effect, the authors found.

Overall, the most favorable ratio of total to high-density lipoprotein cholesterol was achieved with the high MUFA/low GI diet, Dr. Jebb said.

"This study suggests that weight control, rather than diet composition, is the critical element to improve insulin sensitivity -- a risk factor for type 2 diabetes and cardiovascular disease," she added.

Dr. Jebb continued: "Favorable blood lipid profiles, associated with reductions in cardiovascular disease risk, can be achieved by reducing saturated fat and substituting with monounsaturated fat, and by substituting low GI carbohydrates for high GI carbohydrates. The latter change may possibly benefit insulin sensitivity too, but more research is needed to test this fully."

Am J Clin Nutr. Posted online August 25, 2010. Abstract

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