The digestion of the triglyceride proceeds by the removal of fatty acid at the 1 position yielding fatty acid and a diglyceride. The fatty acid in the 3 position is then removed by action of lipase leaving 2-monoglyceride. The removal of fatty acid from the 2-monoglyceride is a slow process. 2-monoglyceride will be converted at a slow rate into 3-monoglyceride by an enzyme called isomerase.
The products of digestion of fat are 2-monoglycerides (about 22 percent), 3-monoglycerides (about 6 percent), triglycerides (3 to 10 percent), diglycerides (3 to 10 percent) and free fatty acids and free glycerol (about 22 percent).
The monoglycerides and free fatty acids are converted into micelle in the presence of bile salts and are absorbed into the intestinal wall. The free glycerol also is absorbed. The 3-monoglyceride is hydrolysed in the intestinal wall by the intestinal lipase to fatty acid and glycerol.
Within the intestinal wall resynthesis of triglycerides takes place. The intestinal wall has enzyme systems for fat synthesis. The resynthesised fat is converted into chylomicrons. The chylomicrons enter the lymphatics through lacteals and are delivered into the circulation via thoracic duct.
The fatty acid composition of chylomicrons of the lymph is different from that of the fat in the diet as fat is resynthesised in the intestines using fatty acids derived from food fat and fatty acids present in bile.
When C-labelled palmitic acid mixed with olive oil is administered orally to rats, the labelled palmitic acid was found randomly distributed in the 1,2 and 3 positions of triglycerides in the chylomicrons of the thoracic lymph showing thereby that complete resynthesis of fats takes place in the intestinal wall.
Short chain fatty acids (C4 — C12 ) which are present in small amounts mainly in butter and coconut oil are absorbed as free fatty acids into the portal vein.
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