Digestion of fats or lipids in human body

  • Fats and oils or collectively called lipids or tryglycerides are digested by lipases.
  • Their digestion starts in the stomach and is nearly completed in the small intestine.
  • Saliva contains no lipase, nor is any fat emulsifying agent present in the oral cavity.

1. Stomach:

  • Stomach also lacks fat-emulsifying agent.
  • However, gastric juice contains gastric lipase, which converts some fats into monolgycerides and fatty acids.
  • The reaction is negligible as the enzyme is sensitive to free acid and is soon destroyed by HCl.

2. Small intestine:

  • In the small intestine, food meets three secretions: bile, pancreatic juice and intestinal juice, all alkaline in nature.

a. Bile:

  • It is secreted by liver and is stored and concentrated by the gall bladder.
  • It contains no enzyme, and, thus has no chemical action on food.
  • Its salts namely, sodium glycocholate and sodium taurocholate, reduce the surface tension of large fat droplets and break them down into small ones, the process called emulsification of fats.
  • It produces a fine emulsion of fats in the aqueous intestinal contents.
  • Bile salts also form a thin coating around tiny fat droplets to keep them from coalescing.
  • The small droplets of fats present large surface area to lipases which increase their action upon them.

Triglycerides ———-> Emulsified triglycerides (by bile)

b. Pancreatic juice:

  • It contains pancreatic lipase, which is the principal fat-digesting enzyme.
  • It hydrolyzes fats in different stages.
  • In the first stage, lipase separates one fatty acid molecule, changing the emulsified triglycerides into a diglyceride.
  • In the second stage, the diglyceride is broken down into another fatty acid molecule and a monoglyceride.
  • In the third stage, the monoglyceride is hydrolyzed to another fatty acid molecule and a glycerol molecule.
  • Thus, a complete hydrolysis of fat molecule gives three fatty acid molecules and one glycerol molecule.
  • However, normally the digestion of fats remains incomplete in the intestine.
  • Hydrolysis of fats is a slow process, and a few hours available for the action of lipase in the intestine are not enough for the completion of fats hydrolysis.


Triglyceride ———-> Fatty acid + Diglyceride

Diglyceride ——–> Fatty acid + Monoglyceride

Monoglyceride ———-> Fatty acid + Glycerol

c. Intestinal juice:

  • Intestinal glands secrete intestinal lipase.
  • This enzyme occurs mainly in the intestinal epithelial cells and only a small amount is released in the intestinal juice.
  • The lipase found in the intestinal juice hydrolyzes some triglycerides, diglycerides and monosaccharides to fatty acids and glycerol like the pancreatic juice.

Digestion of fats or lipids in human body