Medium chain triglycerides (MCTs) are a unique type of fatty acid, by virtue of their structure. The designation ‘medium’ refers to the length of the fatty acids, which is measured by the number of carbon atoms in each fatty acids backbone structure. In the case of medium chain fatty acids, the carbon backbone ranges in length from 6 to 12 carbons. In contrast, long-chain fatty acids (LCFAs) are composed of backbones with 14 or more carbon atoms. The other major distinction is that MCTs are saturated when compared to LCFAs1.
MCT Structure & Function
The unique structure of MCTs impart important differences in their molecular size and water solubility1. These differences affect how MCTs are processed during digestion, absorption and transport within the body, which ultimately explains some of the commonly experienced side-effects with oral use of MCTs1. Because of their smaller size, the medium chain fatty acids that make up MCTs are relatively water soluble compared with LCFAs.
The gut is the first place where the metabolic discrimination occurs for MCTs compared with LCFAs2. Because MCTs have a smaller molecular weight than LCT, they are more accessible to enzymatic digestion by the specialist fat digestive enzyme; pancreatic lipase1,2. As a result. MCT’s are digested more quickly than LCT and are absorbed quicker into the intestinal lumen, where they are subsequently transported by the portal vein to the liver for metabolism/energy production1,2.
MCT Side Effects
Adverse MCT Side Effects
Despite their unique metabolism relative to LCFA, oral ingestion of MCT’s are known to be associated with a number of gastrointestinal side-effects. These include nausea, upset stomach, diarrhea and general gastric discomfort. These side-effects are thought to occur as a result of the body’s failure to upregulate pancreatic lipase production in association with the increase in MCT consumption1. Furthermore, individuals with any degree of bile salt or pancreatic lipase deficiency are likely to experience more adverse gastrointestinal side-effects from oral administration of MCT oil, particularly if starting with aggressive doses.
To best avoid the common side-effects of MCT consumption, individuals are advised to start with very low doses (i.e. 1 teaspoon or 4-5g) and work their way up gradually to 1-2 tablespoons. This will allow the body and digestive tract sufficient time to up-regulate its output of pancreatic lipase.
Beneficial Side Effects of MCTs
The rapid digestion and absorption characteristics of MCTs have been shown to result in improved gastric emptying when compared to LCFAs3. To add to this, studies have shown that when combined with carbohydrate, MCTs increase the rate of gastric emptying compared with a carbohydrate dose equal in calories4. This application of MCTs is thought to be useful for athletes looking to maximise carbohydrate uptake before or during exercise.
There is also weak evidence to suggest that MCTs may improve the absorption of the mineral calcium and magnesium5, particularly in infants6. There is also some evidence MCTs may improve amino acid absorption7.
Medical Applications of MCTs
Because they don't follow the conventional route of digestion, absorption and transport, MCTs are often used in the clinical setting for the treatment of individuals with fat malabsorption syndromes1. Such individuals typically have issues with the lymphatic fat transport system used by LCFAs. Other applications include gallbladder disease or any conditions which increase energy requirements such as retarded growth or severely malnourished patients1, 8.
1. Andre CB, et al. Medium-chain triglycerides: an update. Am J Clin Nutr. 1982;36:950-962.
2. Papamandjaris AA, et al. Medium chain fatty acid metabolism and energy expenditure: obesity treatment implications. Life Sciences. 1998;62(14):1203-1215.
3. Beckers EJ, et al. Gastric emptying of carbohydrate-medium chain triglyceride suspensions at rest. Int. J. Sports Med. 1992;13:581–584.
4. Horowitz JF, et al. Preexercise medium-chain triglyceride ingestion does not alter muscle glycogen use during exercise. Journal of Applied Physiology. 2000;88:219-225.
5. Agnew JE & Holdsworth CD. The effect of fat on calcium absorption from a mixed meal in normal subjects, patients with malabsorptive disease, and patients with a partial gastrectomy. Gut. 1971;12(12):973-977.
6. Tantibhedhyangkul P & Hashim SA. Medium-chain triglyceride feeding in premature infants: effects on calcium and magnesium absorption. Pediatrics. 1978;61(4):537-545.
7. Holtzapple P, et al. Enhancement of non-electrolyte transport in jejunal mucosa by fatty acids. Gastroenterology. 1972;62:849.
8. Tantibhedhyangkul P & Hashim SA. Medium-chain triglyceride feeding in premature infants: effects of fat and nitrogen absorption. Pediatrics. 1975;55:359-69.