Isocaloric Dietary Interventions for Insulin Resistance and the Metabolic Syndrome

In recent decades, the prevalence of obesity has increased dramatically in the United States. Obesity has been associated with an increased risk of the metabolic syndrome, which is characterized by a cluster of metabolic derangements, including insulin resistance, high blood sugar, high triglycerides, low high density lipoprotein (HDL) cholesterol levels, high blood pressure, and inflammation. Lifestyle interventions, including dietary modification, physical activity, and weight loss, form the basis of treatment for individuals with the metabolic syndrome. However, the optimal composition of the diet is not known at this time. Furthermore, due to hormonal and metabolic changes that accompany weight loss, most people find it very difficult to maintain significant weight reductions over time. As a result, weight regain is exceedingly common.

Several dietary patterns, including the Dietary Approaches to Stop Hypertension study diet (the DASH diet) and the low glycemic index diet (low GI diet), may be useful in the treatment of individuals with the metabolic syndrome, even if body weight stays the same. Novel findings from our own pilot study suggest that these dietary patterns may improve insulin resistance and some other features of the metabolic syndrome, even after just two weeks and in the absence of weight loss. In this important follow-up study, the metabolic effects of the DASH diet and the low GI diet will be compared to those of an Western-style control diet. At least 39 overweight, insulin-resistant volunteers with the metabolic syndrome will be studied during a 32-day inpatient admission. All food will be provided, and body weight will be kept stable throughout the study. Subjects will first undergo testing after consuming a Western-style diet for two weeks. They will then be randomized to one of three study diets: the DASH diet, the low GI diet, or the Western-style diet. Testing will again be conducted after 2 weeks of weight stability on the study diet. Testing will include the assessment of insulin sensitivity and other metabolic parameters, such as blood sugar and cholesterol levels, blood pressure, and inflammation. This study will provide important information about the effects of these promising dietary patterns on features of the metabolic syndrome, in the absence of weight loss.