Obesity and type II diabetes mellitus

Pi Sunyer, F. Xavier

ABSTRACT

Obesity has a major effect on the prevalence and severity of diabetes mellitus. The prevalence of reported diabetes is 2.9 times higher in overweight than in non-overweight persons in the National Health Examination Survey (NHANES) data. There is a strong correlation between the relative weight and the prevalence of diabetes in population groups. There have been prospective studies in a number of countries, including the United States, Norway, Sweden and Israel, which have shown that overweight increases the risk of diabetes mellitus. Cross-sectional studies have also shown that obese patients have an increased relative risk for diabetes. Obesity is rare in insulin-dependent type I diabetes mellitus (NIDDM). About 85 percent of diabetics can be classified as type 2 and, of these, 90 percent are obese. The distribution of body fat is important in increasing the risks of developing diabetes. Recently, in prospective study of Mexican Americans, a higher "Centrality Index" (that is, body fat in a central or upper body pattern) has been found to be predictive of the development of diabetes mellitus. In Sweden, a similar independent effect of waist-to-hip ratio as apredictor of diabetes has been found. The relationship of obesity to diabetes mellitus is not totally clear, but some facts are incontrovertible. The accretion of excess body fat is associated with increasing insulin resistance. This is manifested in the liver by increased hepatic glucose output and in the periphery by a decreased glucose uptake by peripheral tissues, primarily muscle and adipose tissue. This is caused by both receptor and post-receptor defects in insulin action. There is a decrease in the number of insulin receptors on the cells of target tissues, but there does not seem to be a significant alteration in the affinity to the receptors for insulin. Insulin receptor binding is decreased. Skeletal muscle is equally and severely resistant to insulin in obese patients with or without NIDDM, while adipose tissue is less insulin-resistant in obesity than it is once diabetes has supervened (AU)