Triglycerides are a type of fat, and they represent the storage form of fatty acids in plants and animals. The fatty acids of triglycerides are classified into saturated, monounsaturated and polyunsaturated types, and each fatty acid type has a role in human nutrition. All dietary triglycerides, especially saturated triglycerides, are utilized as a source of energy. The American Dietetic Association recommends consuming no more than 30 percent of total calories from triglycerides, divided approximately equally between the three types of fatty acids present.
A triglyceride molecule consists of three fatty acid chains each linked through a separate chemical bond to one glycerol molecule. The length of the fatty acid chain can vary from four carbons, as in butter fat, to 22 carbons, as in fish oil. Each individual fatty acid chain may be saturated with no double bonds between carbon atoms, monounsaturated with one double bond or polyunsaturated with multiple double bonds. However, most triglycerides in food, as well as in the human body, are mixed triglycerides containing two or three different types of fatty acids.
Saturated triglycerides are found primarily in animal products. Lamb contains a relatively high percent of saturated triglycerides, beef an intermediate level and chicken a relatively low level. Vegetable fats such as coconut oil and palm oil also contain saturated triglycerides. Although saturated triglycerides are a good source of energy, excessive consumption is associated with high total and LDL cholesterol and VLDL triglycerides, which predisposes to the development of obesity, type 2 diabetes and cardiovascular disease. Moreover, fatty acids derived from dietary triglycerides are incorporated into cell membrane lipids such as phospholipids, and a high saturation level of cell membrane lipids can adversely affect cell membrane function. Therefore, it is recommended to consume saturated triglycerides at no more than 10 percent of your total caloric intake.
Monounsaturated triglycerides are found in both animal and vegetable foods. Plant-based sources of monounsaturated triglycerides include avocados, nuts, vegetable oils and whole grain products. Chicken, beef and pork fat also contain significant amounts of monounsaturated triglycerides. Relative to dietary saturated triglycerides, monounsaturated triglycerides can lower LDL cholesterol and improve insulin sensitivity. When you are trying to lose weight, substitute vegetable foods containing monounsaturated triglycerides for animal foods containing saturated triglycerides.
Polyunsaturated triglycerides can be separated into those containing omega-6 fatty acids and those containing omega-3 fatty acids. Polyunsaturated triglycerides containing the essential omega-6 fatty acid linoleic acid are found primarily in vegetable oils, nuts, seeds and whole grains. Some oils such as soybean, canola and flaxseed oils also contain the essential omega-3 fatty acid, alpha-linolenic acid. The very long-chain omega-3 fatty acid triglycerides are found almost exclusively in ocean fish. Substituting dietary polyunsaturated triglycerides for saturated triglycerides can lower blood cholesterol and triglyceride levels and improve symptoms of type 2 diabetes.
- American Dietetic Association: A Primer on Fats and Oils
- Journal of Clinical Lipidology: Fatty Acids in Cardiovascular Health and Disease - A Comprehensive Update
- Journal of Nutritional Biochemistry: Effects of Dietary Polyunsaturated n-3 Fatty Acids on Dyslipidemia and Insulin Resistance in Rodents and Humans - A Review
- Lehninger Principles of Biochemistry, Fifth Edition; David L. Nelson and Michael M. Cox
- Nutrition Action Healthletter: Face the Fats
- National Institutes of Health; MedlinePlus: Dietary Fats
Michael Peluso is a semi-retired scientist in the field of nutritional biochemistry. He received his M.S. in nutrition from the University of California, Davis and Ph.D. in nutrition from the University of Missouri. Peluso's work has appeared in scholarly publications such as the "Journal of Nutrition," "Lipids" and "Experimental Biology and Medicine."