Medium chain triglycerides (MCTs) have a small molecular size and yield fewer calories than other fats. In fact, coconut oil has an effective energy value of 6.8 calories per gram, while other fats supply 9 calories per gram.

When we eat fat, it's broken down into smaller bundles of of protein and fat called lipoproteins. These lipoproteins are moved into the bloodstream and then shuttled directly into our fat cells. Medium chain triglycerides are different, though. They don't get bundled into lipoproteins and they don't course through the bloodstream, seeking out a fat cell to make fatter. Instead, they go right to the liver where they are used for energy, right then and there. Because of this, you can eat much more coconut oil than you can other oils without the same fat-storing consequences.

In addition MCTs do not require bile salts for digestion. Patients who have malnutrition or malabsorption syndromes are treated with MCTs because they do not require energy for absorption, utilization, or storage.

The names of the medium chain fatty acids found in MCTs are: caproic, caprylic, capric and lauric acid.

References

PDR Health -- Medium-Chain Triglycerides; The medium chain fatty acids (MCFA) in coconut, however, are different. Ingle, D.L., et al. 1999. Dietary energy value of medium-chain triglycerides. Jour. of Food Sci. 64(6):960; Thampan, P.K. 1994. Facts and Fallacies About Coconut Oil. Asian and Pacific Coconut Community. P.1-2; Baba, N. 1982. Enhanced thermogenesis and diminished deposition of fat in response to overfeeding with diet containing medium-chain triglyceride. Am. J. Clin. Nutr. 35:678; Bach, A.C., et. al. 1989. Clinical and experimental effects of medium chain triglyceride based fat emulsions-a review. Clin. Nutr. 8:223; Hill, J.O., et. al. 9. Thermogenesis in humans during overfeeding with medium-chain triglycerides. Metabolism 38:641; Hasihim, S.A. and Tantibhedyangkul, P. 1987. Medium chain triglyceride in early life: effects on growth of adipose tissue. Lipids 22:429; Geliebter, A. 1980. Overfeeding with a diet containing medium chain triglycerides impedes accumulation of body fat. Clinical Research 28:595A; Bray, G.A. et al. 1980. Weight gain of rats fed medium-chain triglycerides is less than rats fed long-chain triglycerides. Int. J. Obes. 4:27-32; Geliebter, A. 1983. Overfeeding with medium-chain triglycerides diet results in diminished deposition of fat. Am. J. Clin. Nutr. 37:1-4; Baba, N. 1982. Enhanced thermogenesis and diminished deposition of fat in response to overfeeding with diet containing medium chain triglyceride. Am. J. Clin. Nutr. 35:678-82; Murray, M.T. 1996. American Journal of Natural Medicine 3(3):7; Hill, J.O., et. al. Thermogenesis in man during overfeeding with medium chain triglycerides. Metabolism 38:641-8; Seaton, T.B., et al. 1986. Thermic effect of medium-chain and long-chain triglycerides in man. Am. J. of Clin. Nutr. 44:630