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The effects of obesity and body fat distribution on splanchnic insulin metabolism and the relationship to peripheral insulin sensitivity were assessed in 6 nonobese and 16 obese premenopausal women. When compared with the nonobese women, obese women had significantly greater prehepatic production and portal vein levels of insulin both basally and following glucose stimulation. This increase correlated with the degree of adiposity but not with waist-to-hip girth ratio (WHR). WHR, however, correlated inversely with the hepatic extraction fraction and directly with the posthepatic delivery of insulin. The latter correlated with the degree of peripheral insulinemia. The decline in hepatic insulin extraction with increasing WHR also correlated with the accompanying diminution in peripheral insulin sensitivity. Increasing adiposity is thus associated with insulin hypersecretion. The pronounced hyperinsulinemia of upper body fat localization, however, is due to an additional defect in hepatic insulin extraction. This defect is closely allied with the decline in peripheral insulin sensitivity.