The purpose of this proposed randomized, controlled trial is to compare the effects of high monounsaturated fat diets and high carbohydrate diets on body weight, body composition, glycemic control, plasma lipids, and other cardiovascular risk factors over a period of one year. At present, no such studies of free-living subjects have been performed. The specific aims of the proposed project are to test the hypotheses that (1) a high monounsaturated fat diet will produce greater weight loss/body fat loss and more successful weight maintenance than a high carbohydrate diet and (2) a high monounsaturated fat diet will result in an improved lipid profile and better glycemic control than a high carbohydrate diet.

The incidence of type 2 diabetes has increased steadily over the last three decades. Although medical nutrition therapy is an integral component of diabetes management, nutrition recommendations for diabetes have often been based on clinical experience and expert consensus, rather than on carefully controlled clinical trials. The expert consensus on medical nutrition therapy is that carbohydrate and monounsaturated fat together should provide approximately 60-70% of total energy intake. This recommendation accommodates parties on both sides of a debate over what constitutes the optimal macronutrient composition of a diet for type 2 diabetic patients. On one side are proponents of high carbohydrate, low fat diets who contend that this regimen promotes the lowering of total- and LDL-cholesterol and is less calorically dense than diets containing a higher percentage of fat. On the other side are advocates of high monounsaturated fat, Mediterranean-type diets who cite data from short-term studies indicating that this approach decreases postprandial levels of plasma glucose, insulin, and triglycerides, and increases HDL-cholesterol more than isocaloric high carbohydrate diets. However, there is concern about the potential for high fat diets to increase energy intake and weight gain among free-living subjects. To make definitive, scientifically-based diet recommendations, it is essential that controlled long-term trials be conducted to demonstrate the health effects of specific percentages of monounsaturated fats and carbohydrates in the diets of persons with type 2 diabetes.

Inclusion Criteria:

• BMI of 27-40 kg/m2
• 30-75 years of age
• Stable body weight for the preceding 6 months
• Diagnosis of type 2 diabetes for at least 6 months prior to enrollment
• HbA1c of 6.5 to 9.0
• Treatment by diet or oral agents only

Exclusion Criteria:

• Pregnancy or lactation
• Active cardiac, pulmonary, renal, liver, or gastrointestinal disease
• Untreated thyroid disease or hypertension
• Hypertriglyceridemia with levels of TG > 500 mg/dl
• Use of insulin
• Use of specific medications that may alter lipid or glucose metabolism (other than the statins)
• Use of medications that commonly cause significant alterations in body weight (e.g., corticosteroids).