The Visceral Adiposity Syndrome in Japanese-American Men

Japanese-Americans have an increased prevalence of non-insulin-dependent diabetes mellitus and coronary heart disease when compared to native Japanese. This increase has been associated with fasting hyperinsulinemia, hypertriglyceridemia, and low plasma levels of high-density lipoprotein (HDL) cholesterol. The purpose of this study was to examine the relationship of both visceral adiposity and insulin resistance to this metabolic syndrome and to the presence of a predominance of small, dense low-density lipoprotein (LDL) particles (LDL subclass phenotype B) that has been associated with increased atherogenic risk. Six Japanese-American men with non-insulin-dependent diabetes, each receiving an oral sulfonylurea, were selected. One or 2 nondiabetic Japanese-American men, matched by age and body mass index, were selected for each diabetic subject, giving a total of 9 nondiabetic men. Diabetic subjects had significantly higher fasting plasma glucose (p=0.0007) and lower insulin sensitivity (S_I, p=0.018) using the minimal model technique than nondiabetic subjects matched for body mass index. Six men (2 with diabetes) had LDL phenotype A and 8 (4 with diabetes) had phenotype B. One nondiabetic subject had an intermediate low-density lipoprotein pattern. Significantly greater amounts of intra-abdominal fat (p=0.045) measured by computed tomography were found in the men with phenotype B while fasting insulin (p=0.070) and triglycerides (p=0.051) tended to be higher. Intra-abdominal fat was significantly correlated with S_I (r=-0.559), plasma triglycerides (r=0.541), plasma free fatty acids (r=0.677), LDL density (relative flotation rate, r=-0.803), and plasma HDL-cholesterol (r=-0.717). S_I was significantly correlated only with plasma free fatty acids (r=-0.546) and tended to be correlated with hepatic lipase activity (r=-0.512, p=0.061). In conclusion, these observations indicate that in non-obese Japanese-American men, the metabolic features of the so-called insulin resistance syndrome, including LDL phenotype B, are more strongly correlated with visceral adiposity than with S_I. It may therefore be more appropriate to call this the visceral adiposity syndrome. Although questions concerning mechanisms still remain, we postulate that visceral adiposity plays a central role in the development of many of the metabolic abnormalities, including LDL subclass phenotype B, that occur in this metabolic syndrome.