Once food enters the epithelial cells of the villi in the small intestine it will pass into either the blood capillary network or into the lacteal. Sugars and amino acids pass into the capillaries largely by active transport by the epithelial cells, while fatty acids and glycerol pass into the lacteals where they recombine to form triglycerides (fats).

The venules coming from the villi join to form the hepatic portal vein which travels to the liver where it divides into capillaries which pass through the liver tissue. The liver then controls the fate of amount and types of sugar and amino acids which will pass through into the general circulation. The fat travels in the lymph system and bypasses the liver to enter the bloodstream at a connection between the lymph system and the venous bloodstream at a point on the inferior vena cava just before the heart. The fat is thus distributed around the body organs where it is stored as adipose tissue. Avoiding the liver prevents the delicate structure of the liver being damaged by excessive fat accumulation.