Medium-chain triglycerides (MCTs) are fats with an unusual chemical structure that allows the body to digest them easily. Most fats are broken down in the intestine and remade into a special form that can be transported in the blood. But MCTs are absorbed intact and taken to the liver, where they are used directly for energy. In this sense, they are processed very similarly to carbohydrates.
MCTs are different enough from other fats that they can be used as fat substitutes by people (especially those with AIDS) who need calories but are unable to absorb or metabolize normal fats.
MCTs have also shown a bit of promise for improving body composition and enhancing athletic performance.
There is no dietary requirement for MCTs. Coconut oil, palm oil, and butter contain up to 15% MCTs (plus a lot of other fats). You can also buy MCTs as purified supplements.
MCTs can be eaten as salad oil or used in cooking. When taken as an athletic supplement, dosages around 85 mg daily are common.
Preliminary evidence suggests that MCTs are a useful fat substitute for those who have difficulty digesting fat. This makes MCTs potentially helpful for people with AIDS , who need to find a way to gain weight but cannot digest fat easily. 1,2 MCTs might theoretically be helpful for those who have trouble digesting fatty foods because they lack the proper enzymes (pancreatic insufficiency), but taking digestive enzymes appears to be more effective. 3
Although this may sound paradoxical given the above, some evidence suggests that MCT consumption might also enhance the body's natural tendency to burn fat.22-24,34 On this basis, the supplement has been proposed as a weight loss aid. Unfortunately, the results of studies have generally failed to find any weight loss benefits. 25,26,29,31,32 Some studies have, however, found that use of MCTs might produce improvements in body composition (ratio of fat to lean tissue). 29,31 A related supplement called structured medium- and long-chain triacylglycerols (SMLCT) has been created to provide the same potential benefits as MCTs, but in a form that can be used as cooking oil. In a preliminary double-blind trial, SMLCT has also shown some promise for enhancing body composition. 30
Athletes often sip carbohydrate-loaded drinks during exercise. MCTs may provide an alternative. Like other fats, they provide more energy per ounce than carbohydrates; but unlike normal fats, this energy can be released rapidly. 14 A number of double-blind trials using MCTs for improving high-intensity or endurance exercise performance have been conducted, but the results have been thoroughly inconsistent. 15-21 This is not surprising, as none of these studies enrolled enough participants to provide trustworthy results.
Larger studies are necessary to discover whether MCTs are really as useful for athletes as the supplement’s proponents claim.
What Is the Scientific Evidence for Medium-Chain Triglycerides?
A double-blind, placebo-controlled study on 24 men and women with AIDS suggests that MCTs can help improve AIDS-related fat malabsorption. 11 In this disorder, fat is not digested; it passes unchanged through the intestines, and the body is deprived of calories as well as fat-soluble vitamins.
The study participants were split into two groups: one received a liquid diet containing normal fats, whereas the other group received mostly MCTs. After 12 days, the participants on the MCT formula showed significantly less fat in their stool and better fat absorption than the other group.
Another double-blind study found similar results in 24 men with AIDS-related fat malabsorption. 12
The body depends on enzymes from the pancreas to digest fat. In one study, individuals with inadequate pancreatic function due to chronic pancreatitis appeared to be better able to absorb MCTs than ordinary fatty acids. 13 However, this didn't turn out to mean much on a practical basis because, without taking extra digestive enzymes, they could only just barely absorb the MCTs; whereas, if they took digestive enzymes, they absorbed ordinary fats as well as MCTs without difficulty.
Studies in animals and humans tell us that MCTs are quite safe when consumed at a level of up to 50% of total dietary fat. 28,33 However, some people who consume MCTs, especially on an empty stomach, experience annoying (but not severe) abdominal cramps and bloating.
The maximum safe dosage of MCTs in young children, pregnant or nursing women, or people with serious kidney or liver disease has not been established.
1. Craig GB, Darnell BE, Weinsier RL, et al. Decreased fat and nitrogen losses in patients with AIDS receiving medium-chain-triglyceride-enriched formula vs those receiving long-chain-triglyceride-containing formulas. J Am Diet Assoc . 1997;97:605-611.
2. Wanke CA, Pleskow D, Degirolami PC, et al. A medium chain triglyceride-based diet in patients with HIV and chronic diarrhea reduces diarrhea and malabsorption: a prospective, controlled trial. Nutrition . 1996;12:766-771.
11. Craig GB, Darnell BE, Weinsier RL, et al. Decreased fat and nitrogen losses in patients with AIDS receiving medium-chain-triglyceride-enriched formula vs those receiving long-chain-triglyceride-containing formulas. J Am Diet Assoc . 1997;97:605-611.
12. Wanke CA, Pleskow D, Degirolami PC, et al. A medium chain triglyceride-based diet in patients with HIV and chronic diarrhea reduces diarrhea and malabsorption: a prospective, controlled trial. Nutrition . 1996;12:766-771.
17. Jeukendrup AE, Thielen JJ, Wagenmakers AJ, et al. Effect of medium-chain triacylglycerol and carbohydrate ingestion during exercise on substrate utilization and subsequent cycling performance. Am J Clin Nutr . 1998;67:397-404.
29. Tsuji H, Kasai M, Takeuchi H, et al. Dietary medium-chain triacylglycerols suppress accumulation of body fat in a double-blind, controlled trial in healthy men and women. J Nutr . 2001;131:2853-2859.
30. Matsuo T, Matsuo M, Kasai M, et al. Effects of a liquid diet supplement containing structured medium- and long-chain triacylglycerols on body fat accumulation in healthy young subjects. Asia Pac J Clin Nutr . 2001;10:46-50.
32. St-Onge MP, Bourque C, Jones PJ, et al. Medium- versus long-chain triglycerides for 27 days increases fat oxidation and energy expenditure without resulting in changes in body composition in overweight women. Int J Obes Relat Metab Disord . 2003;27:95-102.
33. Nosaka N, Kasai M, Nakamura M, et al. Effects of dietary medium-chain triacylglycerols on serum lipoproteins and biochemical parameters in healthy men. Biosci Biotechnol Biochem . 2002;66:1713-1718.
34. Beermann C, Jelinek J, Reinecker T, et al. Short term effects of dietary medium-chain fatty acids and n-3 long-chain polyunsaturated fatty acids on the fat metabolism of healthy volunteers. Lipids Health Dis. 2003 Nov 17 [Epub ahead of print].
35. Han JR, Deng B, Sun J, et al. Effects of dietary medium-chain triglyceride on weight loss and insulin sensitivity in a group of moderately overweight free-living type 2 diabetic Chinese subjects. Metabolism. 2007;56:985-991.
Last reviewed October 2007 by EBSCO CAM Review Board
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