Triacylglycerols, or triglycerides, are molecules your body uses to transport and store fatty acids. Fatty acids are a valuable source of energy for your cells, and they serve as the precursors for sex hormones, cholesterol, vitamin D and other important compounds. Triacylglycerols are constructed from a glycerol backbone to which 3 fatty acids are attached. "The Merck Manual of Diagnosis and Therapy" states that at least 95 percent of the fats in your diet are in the form of triacylglycerols, so their digestion and absorption are important to your overall health.
Gastric Digestion
Chewing helps to mechanically separate the nutrients in your food and prepares them for further digestion. Enzymatic digestion of triacylglycerols begins in your stomach, where gastric lipase removes fatty acids from their glycerol backbones. Vigorous stomach churning helps to emulsify triacylglycerols and exposes them to enzymatic activity, but stomach digestion of triacylglycerols is incomplete. According to the June 2010 issue of "Advances in Physiology Education," only 15 percent of the triacylglycerols in your diet are broken down before food leaves your stomach.
Intestinal Digestion
Triacylglycerols and fragments of triacylglycerols entering your small intestine are emulsified by bile from your gallbladder, which exposes them to attack by lipase and esterase enzymes secreted by your pancreas. The combined activities of bile salts and pancreatic enzymes produce mixtures of fatty acids and monoglycerides, which are absorbed by the cells lining your small intestine. Depending on the length of the fatty acids, they are either passed directly into your bloodstream, where they are bound to proteins and transported to your liver, or reassembled into triacylglycerols, packaged into transport molecules called chylomicrons and then passed into the lymph vessels surrounding your intestinal tract.
Ultimate Fates
Once they reach your circulation, triacylglycerol-rich chylomicrons and protein-bound fatty acids have two interconnected fates. Some are taken up by your muscles and fat cells, where they are either used for energy or stored for future use. Others are processed by your liver, where they are cycled through various transport molecules called lipoproteins. These lipoproteins circulate through your bloodstream continuously until the triacylglycerols they contain are taken up and used by your cells and tissues.
Considerations
Your body has developed efficient mechanisms for digesting, absorbing and processing triacylglycerols, which are also known as triglycerides. The fatty acids in triacylglycerols can be used for your immediate energy needs, stored as fat for future use or routed into synthetic pathways for the production of cholesterol, hormones and other important molecules. Although a high triglyceride blood level is a risk factor for heart disease, triglycerides are an important dietary source of energy and raw materials.
References
- "The Merck Manual of Diagnosis and Therapy, 18th Edition: Lipid Disorders"; Mark H. Beers, M.D., Editor-in-Chief; 2006
- "Advances in Physiology Education"; Insights into Digestion and Absorption of Major Nutrients in Humans; B.E. Goodman; June 2010
