Visceral adipose tissue volume, rather than total body fat or subcutaneous fat, is the primary driver of insulin resistance and the metabolic syndrome through the flux of free fatty acids and TNF-alpha to the liver and peripheral tissues.

We were able to show that insulin sensitivity, as measured by the euglycemic hyperinsulinemic clamp, was negatively correlated with visceral adipose tissue volume in both men and women... and had no significant correlation with subcutaneous adipose tissue volume... The mechanism by which an increase in visceral adipose mass causes insulin resistance... is postulated that insulin resistance results from the direct drainage of free fatty acids and perhaps tumor necrosis factor alpha (TNFa) from the visceral adipose tissue through the portal vein into the liver and beyond into the peripheral tissues.