Fats seem to be a dirty word to many people. Before the low-carb focus in diet trends, dietary fat was the primary target of public and academic condemnation. It is important, especially for athletes, to understand the basic chemistry of fat (not all fats are created equally!) and the metabolism of fat. First, let’s look at some definitions to clear up the air about evil fats…
Lipids – A class of molecules that are composed of triacylglycerols, sterols, and phospholipids.
Triacylglycerol (also called triglyceride) – A glycerol “backbone” molecule with three fatty acids. One gram of triacylglycerol (TAG) provides 9 kcal of energy to the body when utilized.
Glycerol – A three-carbon molecule that is “backbone” of TAGs. By itself, glycerol is a “sugar” and when released from storage, it can be recycled by the liver to create new blood glucose.
Fatty acids – Chains of carbon atoms of various lengths that attach to a glycerol molecule to form TAGs. A fatty acid with no double bonds is called a saturated fatty acid. A fatty acid with one double bond is called a monounsaturated fatty acid and a fatty acid with two or more double bonds is called a polyunsaturated fatty acid.
|An example of an unsaturated TAG
Fats are interesting in how they are stored in the body. Once fats are digested, they are packaged into chylomicrons, which are lipoprotein particles that transport dietary fats from the intestines to other parts of the body1. Once the digested fats have reached their targeted cells, they are either stored or used depending on the person’s physiological state. The infamous “fight or flight” hormones (i.e. adrenaline) and muscular contractions (only up to a certain point though) induce fat breakdown and burning in the processes called lipolysis and oxidation. If the body is in the “restive-digestive” state, the hormones secreted during this stage and the relative lack of muscular activity induce fat building/storage called lipogenesis1.
Dietary fats are physiologically different than other major micronutrients because fatty acids can be incorporated into the phospholipid bilayer of the cell membrane, which ultimately can lead to membrane fluidity changes and different physiological effects of the body, such as inflammation or blood clotting. What is the phospholipid bilayer of the cell membrane you ask? Well, think back to your high school biology days… okay, depending on your age, your biology book might not have covered the phospholipid bilayer. In a nut shell, a phospholipid bilayer is a think polar membrane made up of two layers of lipid molecules. Cell membranes of almost all living organisms and many viruses are made of a lipid bilayer. It serves as a barrier to keep ions, proteins, and other molecules where they need to be and prevent them from “running away.” Phospholipids have a “water-loving” head and a “water-hating” tail. Thus the “water-loving” heads face out and the “water-hating” tails always face inward. And that’s all you really need to know about that, but I could go on for days about the topic.
Here’s a nerdy video of the plasma membrane 🙂
Certain fatty acids are known to be essential, sort of like certain amino acids, because the human body is unable to create them in the body; thus, these fatty acids must be obtained through diet. These essential fatty acids are called linolenic (Omega 3) and linoleic acid (Omega 6).
Omega-3 and omega-6 fatty acids are important in the normal functioning of all tissues of the body. Adequate intake of these essential fatty acids have shown in studies to help prevent atherosclerosis, reduce the incidence of heart disease and stroke, and reduce joint pain among other things2.
Stored cellular fat in the form of TAG is the primary fuel source during fasting periods lacking intense physical exertion1. Research has shown that about 60% of a human’s “fuel mix” at rest – in a fasted state- is from fat1. So, now you think you can become a couch potato and burn fat! Sounds great doesn’t it? But, that’s not how it works. Just sitting there on the couch and watching television requires very little caloric expenditure and thus “60% of nothing is still nothing!”1 So get off your butt and start moving!
The use of fatty acids during physical activity is an interesting relationship. A couple weeks ago I discussed metabolism. If you need a review, click HERE. There is a direct relationship between fat use and exercise duration. The longer you exercise at a low-moderate pace (i.e. your endurance pace and/or Zone 2 heart rate), the greater your fat breakdown and “burning.” However, there is an inverse relationship between fat use and intensity. The more intense you exercise, the less stored fat can contribute (i.e. your body switches to mainly carbs).
It is important to include healthy fats (i.e. monounsaturated and polyunsaturated fats) and in your diet because fats serve the following functions in your body:
- Fat is used by your body for fuel because it is the most energy-dense macronutrient and they provide most of the body’s tissues and organs (including your heart!) with their energy1
- Cell membranes are composed of phospholipids
- Fats are critical for the transmission of nerve signals that generate muscle contractions1
- Serve as a transporter for vitamins A, D, E, and K1
- Provide cushioning for the protection of vital organs and insulation from cold environments1
- Antonio J, et al. Essentials of Sports Nutrition and Supplements. Totowa, NJ: Humana Press, 2008.
- Physicians Committee for Responsible Medicine. Essential Fatty Acids. Available at: http://www.pcrm.org/health/health-topics/essential-fatty-acids. Accessed June 4, 2012.
(Disclaimer: Once again this is for your information only. If you feel you need help with your diet and health then I urge you to seek professional medical and nutrition advice from an expert.)