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The Digestion Process of Fats

author image Michael Long
Michael Long is a practicing nutritionist and started writing in 2010 for various websites, covering topics in alternative healing and nutrition. He has a master's degree in nutrition from Benedictine University.
The Digestion Process of Fats
A sliced avocado on a table. Photo Credit: kwanchaichaiudom/iStock/Getty Images

Experts always tell you to be careful about the fatty foods you ingest. The U.S. Department of Health and Human Services, for instance, specifies that no more than 10 percent of your daily calories should come from saturated fats. But many people don't really know what they’re talking about, scientifically speaking. They should know how the human body digests fats and why they should limit them.

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Starting Point

Many food products have all sorts of fat jumbled with other nutrients, whether in the raw ingredients or added during the cooking process. So your digestive system must break down the components, isolate fats and nutrients, distribute those to the rest of the body and discard what it can’t use. Chewing is the first step. As your teeth break food into soft and smaller particles, your saliva brings in enzymes to work on the food at the molecular level. For instance, salivary amylase acts on glucose, while salivary lipase acts on dietary fats.


When you swallow, food pushes down your esophagus – that pipeline going down your throat and neck. Then it falls into a bag-like organ called the stomach, where the pepsin enzyme furthers breaks down food proteins. Salivary lipase is also still active at this point; it continuously secretes through saliva and naturally accumulates in the stomach, where it hydrolyzes fats. When the lipase and pepsin have done their work, the resulting mush goes through the pyloric valve separating the stomach from the small intestine.

Small Intestine

Your liver and pancreas fill your small intestine with substances that will do serious chemistry with fats and carbohydrates. Bile salts from the liver liquefy the fats in the mush. Meanwhile, the juice secreted by the pancreas carries pancreatic lipase, which breaks the fat molecules down to their simplest forms. According to the U.S. National Digestive Diseases Information Clearinghouse, fats take the longest time to digest. But when the digestion process completes, they will have turned into fatty acids and glycerol. These are readily absorbed into your bloodstream via the small intestine’s enterocytes or absorptive cells, and eventually distributed to the rest of your body.

Easy Storage

Yes, you need fats, but not much. According to the U.N.’s Food and Agriculture Organization, the body needs fatty acids for various vital functions, like the upkeep of cellular membranes, the production of cholesterol, and smooth muscle contractions. There are four types of fats: monounsaturated, polyunsaturated, saturated, and trans. The last two types are the fastest to digest, but tend to raise “bad” cholesterol, or LDL, levels in the blood. Even so, if your daily physical energy needs do not exceed your total consumed calories, whatever extra glucose or fatty acids you’ve produced – good or bad – will store as fat cells in various parts of your body. That’s how you gain weight, get higher cholesterol levels and eventually clog your arteries.

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