Digestion of fats even though starts in mouth, but actual digestion and absorption takes place in the small intestine.
Fat digestion in the mouth, esophagus & stomach
Even though digestion begins in the mouth once, the food is chewing along with saliva, still there is no appreciable fat digestion takes place. Even though there is some lipase secretion by Ebner's gland in the tongue and stomach, there is no significant digestion or breakdown of fat happens.
Liver digestion fat
The liver produces and secretes bile, a substance vital for fat digestion. Bile contains large quantities of bile salts; mostly ionized sodium salts a steroidal derivative by the oxidation of cholesterol. Bile salts attaches with the fat and emulsifies (make in soluble in water) it. This makes droplets of fat broken down into smaller particles that are easier to digest by the enzyme’s lipase.
Pancreas digestion fat
The enzyme that involves in fat digestion is the pancreatic lipase. Enzyme lipase hydrolyzes triglycerides into two fatty acid chains and two mono-glycosides. These hydrolyzed end products are easily be absorb by the small intestine.
Small intestine digestion fat
The fats are insoluble in water, so the fat molecules get into the duodenum as a jelly-like mass. Thus, it is impossible for the pancreatic lipase enzymes to break down fats, since lipase is a water-soluble enzyme and can be only able to break down the surface of the fat molecules.
This difficulty to solve is overcoming by the helps of a substance produced by the liver and stored by the gallbladder called bile, which is entering into the duodenum via the bile duct. Bile produced by the liver can emulsify the fat and make it into small droplets of smaller particle size. Emulsification of fat help allows the enzyme lipase to gain easier access to the fat molecules and accelerates their breakdown by hydrolyzing it into fatty acids and glycerol.
Fat absorption in Small Intestine
Absorption of fat takes about 10 to 15 minutes by million of finger-like projections in the walls of the small intestine called Villi. Each villus is covering by many microvilli that help to increase the absorption area. Inside each villus contains lymph vessels (lacteals) and blood vessels. The lacteals absorb the fatty acids and glycerol into the lymphatic system which in-turn loaded into the bloodstream as lipoproteins after reaction with water-soluble proteins in the blood.
These fatty acids are travel through the bloodstream to the adipose cells or muscle cells, where they are either stored or burnt for energy.
Only 5 % of the digested fats are converting into glucose for energy needs, balance is stored as body fat in the adipose cells. The glycerol portion of the triglycerides (fat) is absorbed by the liver is either converted into glucose or used to burn glucose for energy.
If the lipid levels in the blood drop too low, our body can synthesize lipids from other food sources, such as carbohydrates, or take it from lipid’s storage.
The excess fats that we consume can excrete in the form of fats, or fatty acids, which are the normal component of feces.