The goal of the study is to define the roles played by resistance to insulin-mediated glucose disposal (insulin resistance) and circulating plasma insulin concentrations in: 1) ability to lose weight; 2) reduction of risk for coronary heart disease as a result of weight loss. We hypothesize that in the setting of caloric restriction, manipulating endogenous insulin concentrations will not alter ability of subjects to lose weight, but will lead to different reduction in CHD risk factors. To test this hypothesis, two parallel studs will be performed. First, obese insulin-resistant individuals will be randomized to one of two equally-hypocaloric diets that vary moderately in proportion of carbohydrate and mono/polyunsaturated fats (lower carbohydrate diet will be associated with greater reduction in endogenous insulin secretion). Second, diabetics treated with insulin secretagogues will be compared to diabetics treated with insulin sensitizers with respect to the same outcomes (secretagogues increase insulin secretion and insulin sensitizers decrease insulin concentrations). Endpoints include weight loss, change in insulin resistance, blood pressure, lipid and lipoproteins, markers of endothelial function, daylong insulin and glucose concentrations: these will be compared, in each of the parallel studies, between the group with insulin-stimulating intervention vs the group with the insulin-sparing intervention.
Primary Outcome Measures:
Secondary Outcome Measures:
- Lipid/lipoprotein changes
- Blood pressure changes
- Insulin resistance changes
- Endothelial function changes
| Estimated Enrollment: |
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While obesity, insulin resistance, and diabetes are highly associated, it is not clear whether insulin resistance and compensatory hyperinsulinemia play important roles in the tendency to gain weight and/or inability to lose weight. The role of hyperinsulinemia in coronary heart disease (CHD)is also unclear. The specific aims of the proposed research are as follows:
- To compare insulin resistant versus insulin sensitive nondiabetic overweight individuals with respect to their ability to lose weight on a low calorie diet. CHD risk factors before and after weight loss will also be assessed to determine the degree to which insulin resistance is associated with CHD risk, as well as the impact that differences in insulin resistance have on the metabolic benefits of weight loss
- To determine if weight loss and its associated metabolic benefits vary as a function of the relative amounts of dietary fat and carbohydrate in hypocaloric diets. Because high carbohydrate diets increase insulin secretion, the relationship between dietary composition and change in circulating insulin concentrations will be analyzed with respect to both weight loss and CHD risk factors.
- To quantify and compare the improvement in glycemic control and CHD risk factors associated with weight loss in obese type 2 diabetics, while being treated with 1) an insulin secretagogue (sulfonylurea) or 2) an insulin sensitizer (thiazolidinedione). Manipulation of plasma insulin concentrations with these medications will provide a mechanism by which to evaluate the impact of circulating insulin concentrations on the described outcome measures.
Purpose
