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How Does the Body Digest & Metabolize Fat?

by
author image Carrie Dennett
Carrie Dennett is a Seattle-based registered dietitian nutritionist and journalist. She has been a health, wellness and nutrition writer since 2004, and currently writes a nutrition column for "The Seattle Times." She holds a Master of Public Health in nutritional sciences from the University of Washington.
How Does the Body Digest & Metabolize Fat?
Close-up of halved avocado amongst a pile of avocados. Photo Credit nata_vkusidey/iStock/Getty Images

Not only does the fat you eat help you enjoy your food and feel satisfied after meals, but it also plays important roles in your body. You store some fat for long-term energy needs and use some for short-term energy. Additionally, fat stores help cushion vital organs and protect nerve cells. Most of the fat you eat, digest and metabolize is in the form of triglycerides.

Digestion Part 1: Your Mouth and Stomach

Fat digestion begins when a gland under the tongue secretes the fat-splitting enzyme lingual lipase. Gastric lipase, secreted by cells in the stomach, continues working on the fat molecules as the muscles of the stomach wall act like a blender, churning and mixing stomach contents. Together, this emulsifies the fat by breaking up large fat globules into smaller ones, distributing them evenly. It takes your stomach longer to digest fats than carbohydrates or protein, so higher fat meals may make you feel fuller, longer.

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Digestion Part 2: Your Small Intestine

Most fat digestion happens once your food passes from the stomach to the small intestine. In the upper part of the small intestine, the duodenum, mechanical emulsification continues with the help of bile acids released from the gall bladder, where they are stored after being produced by the liver. Pancreatic lipase, an enzyme secreted by the pancreas, then splits triglycerides apart into smaller parts called diglycerides, monoglycerides and free fatty acids.

Absorption and Transport

Further down the small intestine, these smaller fat components are absorbed by the layer of cells lining the intestinal wall. Smaller fatty acids go straight to the portal vein where they bind to the protein albumin and travel to the liver to be used for energy or turned into longer chains as needed. Larger fatty acids are reformed into triglycerides, then are packaged into lipoproteins called chylomicrons and released into the bloodstream.

Metabolism: Energy vs. Storage

As chylomicrons travel through the bloodstream, they distribute triglycerides to tissues that need it, mostly muscle tissue and fat, or adipose, tissue. About 20 percent of the triglycerides are delivered to the liver, where they are broken apart and either absorbed by liver cells or used to produce energy. All of your cells can use fatty acids for energy, except for those in your brain, red blood cells and eyes.

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