How do medium-chain triglycerides work as a therapeutic supplement?

Overview

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. However, 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.

Requirements and Sources

There is no dietary requirement for MCTs. Coconut oil, palm oil, and butter contain up to 15 percent MCTs (plus a lot of other fats). MCTs can be purchased as purified supplements.

Therapeutic Dosages

MCTs can be eaten as salad oil or used in cooking. When taken as an athletic supplement, dosages around 85 milligrams (mg) daily are common.

Therapeutic Uses

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. 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.

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. On this basis, the supplement has been proposed as a weight-loss aid. The results of studies have generally failed to find any weight-loss benefits. Some studies have, however, found that use of MCTs might produce improvements in body composition (ratio of fat to lean tissue). 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. One placebo-controlled study found hints that use of MCTs by people with type 2 diabetes might improve insulin sensitivity and aid weight loss.

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. 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. 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.

Scientific Evidence

Fat malabsorption. A double-blind, placebo-controlled study on
twenty-four men and women with AIDS suggests that MCTs can help improve
AIDS-related fat malabsorption. In this disorder, fat is not digested; it
passes unchanged through the intestines, and the body is deprived of calories as
well as of 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 twelve 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 twenty-four men with AIDS-related fat malabsorption.

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. However, this
did not 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.

Safety Issues

Studies in animals and humans reveal that MCTs are quite safe when consumed at a level of up to 50 percent of total dietary fat. 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, and people with serious kidney or liver disease has not been established.

Bibliography

Beermann, C., 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 in Health and Disease 2 (2003): 10.

Han, J. R., 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 56 (2007): 985-991.

Matsuo, T., et al. “Effects of a Liquid Diet Supplement Containing Structured Medium- and Long-Chain Triacylglycerols on Body Fat Accumulation in Healthy Young Subjects.” Asia Pacific Journal of Clinical Nutrition 10 (2001): 46-50.

Nosaka, N., et al. “Effects of Dietary Medium-Chain Triacylglycerols on Serum Lipoproteins and Biochemical Parameters in Healthy Men.” Bioscience, Biotechnology, and Biochemistry 66 (2002): 1713-1718.

St-Onge, M. P., et al. “Medium-Chain Triglycerides Increase Energy Expenditure and Decrease Adiposity in Overweight Men.” Obesity Research 11 (2003): 395-402.

_______. “Medium- Versus Long-Chain Triglycerides for Twenty-seven Days Increases Fat Oxidation and Energy Expenditure Without Resulting in Changes in Body Composition in Overweight Women.” International Journal of Obesity Related Metabolic Disorders 27 (2003): 95-102.

Tsuji, H., et al. “Dietary Medium-Chain Triacylglycerols Suppress Accumulation of Body Fat in a Double-Blind, Controlled Trial in Healthy Men and Women.” Journal of Nutrition 131 (2001): 2853-2859.