Why does the removal of visceral fat (a very small percentage of the animal's weight) cause a 40% increase in peripheral glucose metabolism? The omentum is known to be a repository for macrophages and the increase in macrophage numbers is proportional to the increase in adiposity in humans. Both macrophages and adipocytes produce adipokines and cytokines that are known to influence glucose and insulin metabolism. The omentum is also known to be the major contributor of Free Fatty Acids into the portal circulation which adversely affects the hepatic insulin resistance.