Fat -- it’s a nasty word in most women’s minds, evoking images of squeezing into too tight jeans with those dreaded muffin tops hanging out as evidence of eating too much. While you might understandably try to reduce fat in your own diet, your body actually needs some fat. Triglycerides are one important type of fat needed to provide or store energy, and there is a complex, well-integrated system for making it available.
Every day, your body digests and absorbs 50 to 100 grams of triglycerides, according to Ellie Whitney and Sharon Rolfes in their book "Understanding Nutrition." In order to be converted into energy, your body breaks these down into smaller molecules, namely monoglycerides, fatty acids and glycerol. Most of this work is done in the small intestine, with the aid of bile and fat-digesting enzymes known as lipases.
Importance of Emulsification
As triglycerides enter the small intestine from the stomach, a hormone, cholecystokinin (CCK), is released, stimulating the gallbladder to secrete bile. Bile, due to its chemical structure, is an emulsifier, attracting both fat and water molecules. Large triglyceride molecules are drawn into the water matrix, where they are emulsified into smaller particles. This then prepares them for further breakdown by pancreatic lipase enzymes. Bile, on the other hand, is reabsorbed into the blood and travels back to the liver where it is stored.
A triglyceride molecule consists of a glycerol molecule and three attached fatty acids. The fatty acids are removed from glycerol one at a time by pancreatic lipase enzymes. Because lipase enzymes are water-soluble, they only work on the outside of the fat molecule as it is immersed in the surrounding water. Even though the small intestine contains a large amount of lipase, the smaller fat molecules resulting from emulsification provide a greater surface area for the enzymes to work. Most often only two fatty acids are removed from a triglyceride, leaving one fatty acid still attached -- a monoglyceride. The process of removing fatty acids from glycerol, called hydrolysis, also requires water.
Absorption and Delivery
Monoglycerides and fatty acids, some still connected with bile, form complexes called micelles. According to Colorado State University, micelles are very small, only 4 to 8 nanometers in diameter. Cells in the intestine absorb these micelles, repackaging them along with proteins into molecules called chylomicrons. Chylomicrons travel throughout the body via the blood, delivering the by-products of triglyceride digestion wherever needed. As these lipid fragments are removed, the chylomicrons become progressively smaller and smaller in size, a process normally taking 14 hours, note Whitney and Rolfes. The liver then removes the rest of the unneeded chylomicrons from the blood, where they are further degraded and reassembled to start the absorption and delivery process again.
- Understanding Nutrition; Ellie Whitney and Sharon Rady Rolfes
- Colorado State University: Absorption of Lipids
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