The predominant dietary lipids include triglycerides, listed on labels as fat, and cholesterol. You use triglycerides as a source of energy for your cells, while cholesterol -- despite its reputation as a harmful biomolecule -- has a number of essential roles in maintaining the health of your cells and systems.
Triglycerides
Triglycerides, or storage fats, are in many foods. Saturated fats, which tend to be solid at room temperature, come primarily from animal sources. Unsaturated fats -- the most heart-healthy of the triglycerides -- come primarily from plant sources, though you also obtain them from cold water fish. Trans fats are processed fats, and are the least healthy fat in terms of your cardiovascular system. Any greasy substance -- oil or solid fat -- contains triglycerides.
Triglyceride Use
You can metabolize triglycerides for immediate energy; the triglyceride molecule breaks apart into three smaller molecules called fatty acids, and one molecule called glycerol, which is similar to alcohol. Your cells break the fatty acids apart two carbons at a time and then burn these two-carbon chunks to generate energy and carbon dioxide, which is a metabolic waste product. You can also store triglycerides in fat tissue for later use.
Cholesterol
Cholesterol, despite its reputation, is an important biomolecule. Uses include helping to maintain cell membranes at an appropriate level of fluidity. Without sufficient cholesterol, cell membranes are too liquid. Further, cholesterol is the starting point for metabolic synthesis of several hormones, including estrogen and testosterone, and for synthesis of vitamin D, which helps you take up calcium from the digestive tract.
Cholesterol Sources and Excretion
You can obtain cholesterol from foods, but your cells can also make it from fats. For this reason, there's an important relationship between the fats you eat and the cholesterol in your bloodstream. Too much cholesterol increases your risk of heart disease, and both saturated and trans fats increase the amount of cholesterol going out to your body cells. Unsaturated fats, however, fill your body's need for the energy that comes from fat without increasing the cholesterol headed out through the bloodstream to your cells.
References
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- "Biochemistry"; Mary Campbell, Ph.D. and Shawn Farrell, Ph.D.; 2005
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