Dietary fat molecules are not absorbed directly and must be broken down into smaller molecules through a process called hydrolysis. Lipase enzymes hydrolyze fats from the moment the fat hits your mouth because they are secreted from your tongue, stomach and pancreas.
After hydrolysis occurs, your body absorbs fat through a complicated process. Fats are insoluble in water - or incapable of being dissolved - so your body must provide aggregates to turn your fat soluble.
Fat Absorption Messaging System
Large quantities of fat cannot enter your bloodstream at once. If this occurred, your health would be at great risk. Your intestinal tract sends messages to your stomach once an adequate amount of absorbable fat has entered the intestinal cells. This triggers your stomach to hold the remaining fat until your body is ready to absorb more.
This process can take up to four hours, slowing the emptying of stomach content. When fat is present in your stomach, you feel satiety longer. If you eat healthy fatty acids and smaller fat molecules, this can work to your advantage. However, the wrong fats can cause fermentation and actually induce greater hunger.
Fat Soluble Aggregates
Once enzymes break down fat, your body is left with an insoluble form of fat. This fat cannot be readily absorbed as a nutrient, so your body excretes bile acid that works as a detergent to create fat globules known as aggregates. These fat aggregates are transported to the small intestine for direct absorption by the body.
Your body begins absorbing this soluble fat in the duodendum (the first part of your small intestine), but a majority of absorption occurs in the middle part of your intestine known as the jejunum.
Formation of Fats
Fats become diffused to the intestinal cells and enter the intestinal lining as split fat molecules. Intestinal lipase furthers the digestive process by forming triglycerides, cholesterol and phospholipids within these cells. These fat molecules are given a protein protection layer, allowing them to pass between cells into the villi. The villi that absorb fats are called lacteals. The lymph in the lacteals appears milky white due to the high fat content.
Lymphatic Pump System
After passing into the villi, a majority of fatty acids are pushed by the lymphatic pump system. About 80 to 90 percent of digested fats are absorbed this way. The other remaining amount absorbs directly into the bloodstream to enter the liver. The fatty acids carried by the lymphatic pump system are brought into blood circulation through the thoracic duct. Once these nutrients are released into the blood, they are processed by the liver. Some fats are an exception to this process including medium-chain triglycerides (MCTs).
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