Medium chain triglycerides were introduced to the bodybuilding world in the late 80's by John Parillo. They were touted as a fat that behaved like a carbohydrate. Medium chain triglycerides were used to replace long chain fats (ordinary fats) which were much more likely to end up expanding your waistline. The combination of MCTs with a high carbohydrate diet was supposed to be the answer for bodybuilders trying to lose fat and build muscle. Although MCTs were received with much fanfare, interest soon waned as bodybuilders found the combination to be ineffective. It is not surprising that this approach did not produce results because it does not take advantage of all of the special properties of MCTs. The recent popularity of lower carbohydrate diets like the Zone diet justifies another look at MCTs. The special properties of MCTs make them ideal for optimizing this high tech dieting approach. Medium chain triglycerides are usually made by lipid fractionation of coconut oil. Unlike normal triglycerides (long chain triglycerides or LCTs), which are 16-20 carbons long, MCTs contain 6-12 carbons (A triglyceride is 3 fatty acid molecules attached to a glycerol molecule). This gives MCTs several unique characteristics. Compared to long chain triglycerides, they require less bile salts and pancreatic enzymes for digestion and they are rapidly absorbed into the portal system. Because MCTs bypass the normal, complicated digestive processes of LCTs, they enter the bloodstream much more rapidly than long chain fats. LCTs are combined with protein and enter the bloodstream via the lymphatic system. The largest percentage of these LCTs are disassembled and moved into the fat cells where they are reassembled and stored as body fat (Brooks and Fahey, 1985). Therefore, LCTs present in the bloodstream are likely to be stored as fat. MCTs, however, are disassembled and enter the bloodstream as medium chain free fatty acids (MCFFAs). MCFFAs are immediately available for metabolism by muscle and the liver. In fact, most of the MCFFAs are taken up by the liver and metabolized (broken down) by beta-oxidation in the liver. Only 1-2% of MCTs become body fat (Geliebter et al, 1983) (Baba, Bracco, and Hashim, 1982). The MCFFA is oxidized to acetyl-CoA in the liver. This acetyl-CoA can be further metabolized or used to make a long chain free fatty acid (LCFFA). This LCFFA can be attached to a glycerol to make a long chain triglyceride which can be stored as body fat. Remember, however, that only 1-2% of MCTs are used to make body fat (in contrast, most LCTs are stored as fat). To Summarize: LCTs - Normal, long chain triglycerides enter the bloodstream as triglycerides, are disassembled at the adipocytes (fat cells), enter the fat cells, are reassembled and stored as triglycerides (only a small percentage are metabolized by the liver). MCTs- Medium chain triglycerides enter the bloodstream as medium chain free fatty acids (they are disassembled before they enter the bloodstream), most are taken up rapidly by the liver where they are metabolized (only 1-2% are used to form body fat). Normal dietary fat (LCTs) is more easily stored as body fat than carbohydrates. Carbohydrates have to be metabolized to acetyl-CoA, linked together in chains to form fatty acids and then linked to a glycerol molecule to form the body fat in the form of a triglyceride. Since MCTs are less likely to become body fat than LCTs and enter the bloodstream more rapidly (even more rapidly than glucose), they behave more like carbohydrates than fats. However, MCTs do not stimulate insulin production, but carbohydrates do. Insulin is used to move carbohydrates into the fat cell. To someone trying to lose body fat, insulin is the enemy. Insulin turns off fat burning and turns on fat storage. It is the reduction of this insulin surge produced by a high carbohydrate diet that is the thrust behind the Zone diet popularized by Barry Sears. Dr. Sears ties the overproduction of insulin to obesity, hyperlipidemia, high cholesterol, heart disease and other health problems. The solution proposed by Dr. Sears is to reduce carbohydrate intake to 40% (as opposed to the 60-70% favored by some athletes) of the calorie total. In decreasing the carbohydrate intake, fats are increased to 30% of the total calories. This has been the major criticism made by the Zone diet opponents. This sets up a seemingly irreconcilable dilemma. If you keep your caloric intake constant and decrease carbohydrates, you must increase fat (LCTs) and risk greater fat deposition. If you decrease fat intake, you must increase carbohydrates and deal with the associated health problems associated with the over production of insulin. Enter medium chain triglycerides! MCTs can be used to replace most of the LCTs in a Zone diet. Remember that MCTs are metabolized like carbohydrates but do not induce the production of insulin. What this does is gives you a low fat diet that is also low in carbohydrates. In other words, you get the best of both worlds. You reduce the potential for greater fat storage by reducing LCTs, and you reduce insulin production by reducing carbohydrates. In the past, bodybuilders have used MCTs to replace the small amount of fat in an already low fat diet under the assumption that almost all fat was bad. This was a mistake because the high carbohydrate intake and concomitant overproduction of insulin made fat loss difficult. The optimal way to use MCTs is to replace some of the fat with MCTs. With this approach you can take advantage of the low carbohydrate benefits of a Zone type diet while still eating relatively low amounts of ordinary fat (LCT). If you compare the graphs below of the typical low fat diet to the graph of an example "MCT Zone Diet" you will see that although the fat slice has been reduced, the carbohydrate slice remains the same size. This MCT Zone diet achieves the recommended 40% carbohydrates and 30% protein with only 10% of the calories from LCT fats. Note that the MCT low fat diet (the ineffective approach which uses MCTs to replace fats) reduces the carbohydrate slice only slightly. You can see that the MCT Zone diet is the better approach and truly takes advantage of the special qualities of MCTs. Normally 40% carbohydrates is low enough to keep insulin production under control. If you have been following a Zone Diet and are very insulin resistant, you might also consider replacing some carbohydrates with MCTs to reduce insulin secretion. A diet of 30% carbohydrates, 30% protein, 20% fat, and 20% MCTs may be more effective for you. By reducing your carbohydrate amount to 30% of total calories, you are reducing total insulin secretion, yet you are still taking in the same amount of total calories which prevents metabolism problems associated with low-calorie diets. Some people experience intestinal discomfort when they begin MCT supplementation. This is normal and is due to the rapid absorption of the MCTs. It is recommended that you begin with no more than ½ tablespoon at a time and always take MCTs with food. You may increase the dose as tolerance allows. Do not take too much initially or on an empty stomach since severe intestinal discomfort can result. MCT oil should not be used in cooking. When fried, the MCT's give off a very undesirable petrochemical aroma. Also, the enzymes in other ingredients in baking can break down MCT's into the component fatty acids which give it a soapy flavor. It is best to use MCT's in a protein shake or some other non-cooked form. You may want to start with getting 5% of your calories from MCTs. You should gradually be able to work up to 2 or more Tbsp per day depending on your weight. If you have no intestinal problems with MCTs, you may want to try increasing up to a 20% MCT diet to further reduce LCTs and/or carbohydrate consumption. Researchers have replaced up to 60% of their subjects caloric intake with MCTs with no problems by gradually introducing them into their diets. Notice that we did not alter the amount of protein in your diet during this discussion. It is recommended that you do not reduce protein consumption since the Zone diet is based on determining the minimum amount of protein that is needed to maintain and grow muscle mass. References 1. Baba, Bracco, and Hashim, Enhanced thermogenesis and diminished deposition of fat in response to overfeeding with diet containing medium chain triglyceride. Am. J. Clin. Nutr. 35: 678-682 (1982). 2. Geliebter, Torbay, Bracco, Hashim, and Van Itallie, Overfeeding with medium chain triglyceride diet results in diminished deposition of fat. Am.J. Clin. Nutr. 37: 1-4 (1983). 3. Brooks and Fahey, Exercise Physiology, Lipid Metabolism, Macmillan Publishing Company, New York (1985). No duplication or reproduction of this article (or any other Netrition web page) is allowed in any form without written permission from Netrition.