Medium Chain Triglycerides: The little fatty acid chains that can do big things.

What are Medium Chain Triglycerides?

Dietary fats are made up of carbon chains, and these can be anywhere from 2 – 22 carbon atoms long.  Most of the fatty acids in Western diets are long chain,  with 12 or more carbons in the chain.  Medium chain fatty acids have between 6 and 10 carbons.  Because of their shorter length they are metabolized differently.

MCTs resemble carbohydrates more than they do fats.  They are more water soluble.  Because of this they don't require bile to break down, and they are broken down more quickly.  They enter the blood stream faster and are taken directly to the liver, where they are used as an immediate source of energy.  Less MCTs are converted to fat than longer fatty acids.

Where are they found, and what are they good for?

MCTs are found in milk fat, palm oil and coconut oil.  They are also made commercially and are available as liquid or capsules.  The commercial formulas don't hold up well to cooking, because heat makes them oxidize and break down, but they can  be used as al salad dressing or taken as a supplement. 

Since the 1950s MCTs have been used as part of the formula for patients who can not digest fats properly due to illness.  They are given in IV units to people who need parenteral nutrition.  These include people suffering from severe trauma such as burns, or newborn babies who need supplemental nutrition.  People suffering from jaundice, Crohns disease, celiacs, cystic fibrosis, pancreatitis and other illnesses may get MCTs as a supplement to their diet. 

In the 1980s MCTs became a popular source of energy for people engaged in high-level sports such as bikers or marathoners.  High carbohydrate diets had been popular for providing quick energy, but carbs also stimulate insulin, which causes your body to deposit fat.  MCTs provide quick energy as well, but since they are a fat and not a carb, they don't stimulate insulin, and you don't have the problem with weight gain.  MCTs do stimulate thermogenesis, which is the process where your body produces heat by increased burning of fat.  This is a good thing for people who are trying to lose fat.

People who suffer from epileptic seizures have been shown to benefit from a diet high in MCTs.  They also tend to lower blood sugar slightly, and this is beneficial for diabetics.  They have been shown to be antioxidants and have anticoagulative effects, which can help with heart disease.

Why don't I just start eating a diet of strictly MCTs?

Before you start adding palm oil to your food and thinking the fat will just melt off, you should know that to get any meaningful weight loss you would need to eat about half your calories in the form of MCTs.   For a typical adult male we are talking about 1200 or so calories a day of fat.  That's about 130 grams of fat per day.  Fats should only make up about 30% of your calories each day, or for that adult male eating 2400 calories, he should have about 80 grams of fat.  So in order to use MCTs to actually make your body burn fat, you would have to be eating a very unhealthy (and unpalatable) amount of fat.

Aside from that level of fat in the diet being unhealthy, a diet high in MCTs also has some side effects.  These include gastrointestinal upsets such as diarrhea, and increased levels of cholesterol and triglycerides.  This occurs when the MCT level goes above 10% of calories.  People who have complications from liver disease should not take MCTs, as they are processed by the liver.  Also, MCTs do not contain any of the essential fatty acids that we need to survive.  Therefore, a diet of strictly MCTs would be deficient in nutrients that you need.

Studies done with MCTs

A study published in the Journal of Nutrition in 1992 showed that rats fed a diet with MCTs instead of LCTs had a greater energy expenditure, and only gained 1/3 as much weight.

Human studies comparing the two types of fatty acids have only been done for short periods of time.  In a study published in American Journal of Clinical Nutrition in 1991, the energy expenditure of healthy adult men was 65% higher when they were fed MCTs than when they were fed LCTs.  Also, energy expenditure was higher with MCTs than with carbohydrates, though the difference wasn't as great.  The results persisted even for 7 days, as was found in a study published by Metabolism in 1989. 

However in 1999 the American Journal of Clinical Nutrition published a study done with women that showed after 14 days the energy expenditure of MCTs was no longer greater.  This suggests that the effect diminishes over time.  On the other hand, it's been found that women do not respond to MCTs with increased energy burned nearly as well as men do.  Well, just one more reason the cards are stacked against us, ladies!  

Studies have shown that animals given a diet of MCTs instead of LCTs have less fat cells, smaller fat cells and a lower body weight.  This has not been born out in studies on obese humans.  A study published in the International Journal of Obesity in 1998 showed that people eating a diet high in fish oil, which has LCTs, actually had fewer fat cells than people who ate a diet high in MCTs.

In animal studies MCTs have been shown to increase satiety (feeling of fullness) and decrease food intake.  Once again, this hasn't been strongly shown in human studies.  When people were given high MCT foods at breakfast, they did have a lower calorie intake at lunch, but by supper time their food intake was back to normal.  This suggests that if there are effects, they are temporary.  (American Journal of Clinical Nutrition, 1998)

The jury is still out on whether MCTs can be useful in treating obesity or helping with weight control.  Not only are there no long term studies to show they work, but researchers have not been able to pinpoint why they have the effect that they do in animals.  Various hormones have been studied, but none of these are found to be secreted exclusively when someone eats MCTs.

What does it all mean?

If you are an endurance athlete you can certainly benefit from using MCTs as an energy source.  And there are many health benefits to including MCTs in your diet, as long as you don't have liver disease.  Some people with certain health problems may want to take a higher level of treatment under a doctor's care.  Perhaps someday soon there will be a program to treat obesity that includes MCTs.  But for now the average person should not eat more than 30% of your calories in any kind of fat.  Also, don't eat ALL your fat in the form of MCTs, because then you are missing out on the essential fatty acids, which your body needs to survive.  Studies have shown that eating more than 10% of your calorie intake as MCTs can raise your cholesterol level.  As with most things, MCTs can be part of a healthy diet but you shouldn't overdo them.

Journal of Nutrition Study on Physiological Effects of Medium Chain Triglycerides, 2002