PATHOPHYSIOLOGY AND PATHOGENESIS OF VISCERAL FAT OBESITY

Based on the analysis of fat distribution by computed tomography (CT) scans, the classification scheme for obesity should include visceral f at obesity in which fat accumulation is predominant in the intra-abdom inal cavity. Obese subjects with visceral fat accumulation more freque ntly demonstrate impairment of glucose and lipid metabolism than those with subcutaneous fat accumulation. We have shown that visceral fat o besity is present in almost 90% of obese patients with ischemic heart disease. Even in non-obese subjects, visceral fat accumulation is corr elated with glucose intolerance, hyperlipidemia and hypertension. Fort y percent of non-obese subjects with coronary artery disease (CAD) had increased visceral fat. In non-obese subjects, visceral fat area asse ssed by abdominal CT at the level of the umbilicus correlates with met abolic risk factors, whereas in obese subjects the visceral fat area t o subcutaneous fat area ratio provides a more significant correlation. From clinical and basic investigations, aging, sex hormones, excess i ntake of sucrose and lack of physical exercise have been suggested to be determinants for visceral fat accumulation. Since intra-abdominal f at (mesenteric and omentum fat) has been shown to have high activities of both lipogenesis and Lipolysis, its accumulation can induce high l evels of free fatty acids, a product of lipolysis, in portal circulati on, which go into the liver. Excess free fatty acids may cause the enh ancement of lipid synthesis and gluconeogenesis as, well as insulin re sistance, resulting in hyperlipidemia, glucose intolerance and hyperte nsion and finally atherosclerosis. Thus we propose a disease entity, v isceral fat syndrome,which may increase susceptibility to atherosclero sis due to multiple risk factors induced by visceral fat accumulation.