If you are familiar with the ketogenic lifestyle, then it is likely that you have heard about MCTs or medium chain triglycerides. You may know that ketogenic dieters often add MCTs to their coffee in the form of oil or powder. However, MCTs have also been used in the clinical world since the 1950s to increase energy intake in individuals suffering from malabsorption disorders (1). Despite its popularity, most are not fully aware of how these fats work or their capabilities. This article aims to shed some light on the science behind MCTs and how they can be effectively incorporated into your diet.
What are MCTs?
Dietary fats and stored fats are both made up of molecules known as fatty acids. Fatty acids can be classified as saturated, monounsaturated, or polyunsaturated depending on their degree of saturation. The joining of fatty acids together results in the formation of triglycerides. There are three different classifications for triglycerides based on carbon chain length: short (SCTs), medium (MCTs), or long (LCTs). Saturated fats that are comprised of 6-10 carbon atoms are classified as medium-chain triglycerides and are structurally different from long-chain triglycerides (LCTs), which contain 12-18 carbon atoms. Additionally, MCTs are bound to glycerol and contain 3 fatty acids. MCTs can be made up of caproic (C6 or 6 carbons), caprylic (C8), capric (C10), and lauric (C12) acids. Due to their shorter carbon chain length, MCTs have a unique metabolic effect on the body. Despite its slightly longer carbon chain length, lauric acid still possesses characteristics similar to MCTs.
MCTs, like all triglycerides, can be metabolized for the production of energy. However, unlike other triglycerides, MCTs are less likely to be stored as fat or used for de novo fatty acid synthesis because they can be rapidly digested due to their shorter carbon chain length. The shorter chain length of MCT’s allows them to be broken down to medium chain fatty acids and diglycerides by various enzymes, such a pancreatic lipase, contained within our saliva and gastric juices. Following this breakdown, medium-chain fatty acids (MCFAs), since they are soluble, move from the GI tract to the liver for immediate oxidation and energy production (1). On the other hand, long-chain fatty acids (LCFAs) require 1) pancreatic enzymes for digestion and 2) transportation from the GI tract to the lymphatic system, giving them a greater chance of being taken up by adipose tissue for storage. This is one of the characteristics that makes lauric acid slightly different from the other MCTs. Lauric acid has a greater ability to enter the lymphatic system, meaning that they are more likely to be stored as fat and will not produce energy as quickly as other MCTs.
Another reason for the rapid digestion of MCTs is their ability to diffuse directly into the mitochondria for energy production without the aid of a transporter upon entry into the cell. Fatty acids that contain more than 12 carbon atoms (LCFAs) require the aid of carnitine (CPT1) to be transported into the mitochondria, while fatty acids with fewer than 12 carbon atoms do not. MCTs can be metabolized at rates similar to glucose metabolism, which is why they may be considered a superior fat source (1). MCTs produce 10% fewer calories compared to their long-chain counterparts.
For decades MCTs have been prescribed to individuals who suffer from malabsorption syndromes, disorders that occur as a result of poor absorption of nutrients in the small intestine. Since then, a variety of other uses for this particular fat has been found. Most people are unaware that MCTs are used in the hospital setting daily, but MCTs can commonly be found in many of the intravenous feeding solutions that are given to patients suffering from various illnesses. Since MCTs can be rapidly digested and contain a high caloric intake, they can provide a nearly instantaneous supply of nutrients and energy for those suffering from illness or recovering from surgeries that result in loss of appetite. Let’s further discuss the additional benefits that can accompany the use of MCTs.
It has long been noted that fat is essential to the growth and development of children. In fact, the breast milk of a mother contains 40 to 50% fat with a portion of this fat containing MCTs. For this reason, babies are typically born fat-adapted and in some state of ketosis. These fats are important to the development of the brain in children and are often incorporated into formulas of babies who are not receiving traditional breast milk. Furthermore, babies who are born with low birth weight are often fed intravenous solutions that contain MCTs to allow for sufficient nutrient intake and growth. This is important because low birth weight can result in decreased IQ, speech, and reading impairments (2).
It is commonly thought that MCTs possess a powerful weight loss potential due to their effect on thermogenesis and metabolic rate. It has been demonstrated that MCTs lead to greater thermogenesis and energy expenditure following a meal compared to meals containing LCFAs (3). However, an increase in thermogenesis does not necessarily mean a reduction in body fat. Many studies demonstrate an increase in fat oxidation following MCT consumption, but it is possible that fat oxidation could appear higher due to oxidation of MCTs rather than oxidation of body fat.
While an increase in energy expenditure may not be the greatest predictor of fat loss, there are other mechanisms in which MCTs play an important role that may affect fat loss. Additionally, it has been demonstrated that MCTs can have a profound effect on food intake and satiety, or perceived fullness. In a study conducted by Stubbs and Harbron, it was found that various amounts of MCTs were associated with decreased food intake, with higher MCT consumption leading to the greatest decrease in total food intake (4).
In another study, in which men were given breakfasts with varying fat type (olive oil, MCT, lard, or fat substitute), it was found that men consuming MCTs with breakfast voluntarily consumed less food at lunch (5). However, their food intake did not vary at dinner, indicating that the satiating effects of MCTs may be short-lived. Taken together, the potential for increased energy expenditure and decreased food intake can explain a possible mechanism for MCTs’ effect on weight loss.
One reason why we may not always see an increase in weight loss due to MCT intake could be from de novo fatty acid synthesis. De novo fatty acid synthesis is the production of fatty acids from various substrates found within the body. It has been shown that excess acetyl-CoA that is not used for ketone production can result in the formation of LCFAs. In a study by Christensen (7), it was demonstrated that C12 or lauric acid possesses the ability to be rapidly converted to C16, a longer chain fatty acid. Interestingly, this occurred following a glucose refeed, which has been shown to alter the rate of MCFA metabolism (8). The fact that some studies have failed to demonstrate weight loss could be a result of the type of MCTs administered, the amount given, or the addition of carbohydrates in the diet.
Energy and Performance
Due to their rapid absorption and metabolism, MCTS can produce energy at a high rate as well as increase plasma ketone levels, which can be important for a variety of functions. This makes it easy to see why MCTs may be a preferred fuel source for many athletes, especially those who are consuming low-carbohydrate diets. Additionally, it has been demonstrated that having an increased amount of free fatty acids can spare the utilization of carbohydrates during exercise, even in the presence of carbohydrate consumption (9)! These results suggest that MCTs could have a glycogen sparing effect, which could be essential for the endurance athlete, especially since depleted carbohydrate stores is a major cause of exercise exhaustion in athletes who are not in a fat-adapted state.
Another benefit of MCTs, which pertains directly to ketogenic dieters, is the production of ketones from these fats. If you recall from my Understanding Ketosis article, ketones are produced by the liver as a result of increased fat oxidation. In short, when fats are oxidized in the liver they result in the production of acetyl-CoA, which can then enter the mitochondria of the cell and be used by the Krebs cycle to produce ATP or energy. When there is an abundance of acetyl-CoA, a result of increased fat oxidation, the excess substrate not used by the Krebs cycle can be used for the formation of ketone bodies, which are then released from the liver to be utilized by extrahepatic (outside the liver) tissues. The rapid digestion of MCTs can result in this buildup of acetyl-CoA and the subsequent production of ketone bodies (10,11). There is discrepancy as to whether MCTs can actually achieve this. Research has demonstrated that coconut oil by itself does not result in a significant rise in plasma ketone levels (12). However, the same researchers found that when isolating lauric acid (the primary “MCT” in coconut oil), there was an increase in ketone production in astrocytes (cells within central nervous system). For this reason, isolated MCTs may be a better option for those trying to increase ketone production. However, make note that there is also research suggesting that it takes substantial amounts of MCTs to actually result in ketone production (13).
As we know, ketones have the ability to act as an alternative fuel source for the brain, and because MCTs can increase ketone production, we can assume that they also have a similar ability to improve cognition. Currently, there is some data demonstrating MCTs having an effect on memory and learning; however, most of these studies are in animals and the results are conflicting meaning they vary across different study designs. In a small pilot study conducted on patients with mild cognitive impairment, it was found that MCTs led to an improvement on cognitive testing (14). While this is a small population size, it does give promise to the cognitive benefits of MCTs.
I previously mentioned that the use of MCTs in the clinical setting started with disorders of fat metabolism. Since then we have seen the potential for MCTs, by themselves or in addition to other therapeutic strategies, to provide great benefit on a variety of different diseases and disorders.
The ketogenic diet has long been used as a treatment option for children suffering from epilepsy, specifically drug-resistant epilepsy. Additionally, it has been demonstrated that the addition of MCTs before bed led to improved nocturnal seizure control (15).
There have been several studies demonstrating that MCTs can improve risk factors associated with diabetes in those already diagnosed. This is primarily through the hypoglycemic effect of MCTs which leads to blood glucose control and an increase in insulin sensitivity (16).
Earlier we discussed the effect that MCTs can have on brain function, which makes it no surprise that they can also have a positive effect on neurodegenerative diseases such as Alzheimer’s and dementia. One study demonstrated increased cognition in patients with mild to moderate Alzheimer’s disease when given between 10 and 20g of MCTs daily (17). Alzheimer’s is a disease characterized by impaired brain metabolism. Since ketones have been shown to possess the ability to enter the brain of ALZ patients, the mechanism behind the MCT benefits is likely the resulting ketone production. This could also make the use of MCTs beneficial in those suffering from Parkinson’s disease. A great TedTalk by our colleague Dr. Mary Newport explains a case in which she used MCTs in the form of coconut oil for her husband who had Alzheimer’s.
We also have some preliminary data suggesting that MCTs can have a cholesterol-lowering effect and can aid in the prevention or treatment of cardiovascular disease (18).
There are a variety of additional potential uses of these fats in the medical field, even for such diseases as cancer (19). As with many of the diseases discussed above, this may be through the ketosis that occurs as a result of the MCTs.
After hearing how important of a tool MCTs can be, you may be wondering how you incorporate these fats into your diet.
MCTs can be found in a variety of food sources such as coconut oil, palm kernel oil, cheese, butter, milk, and yogurt. Of the foods listed, coconut oil contains the highest percentage of MCTs; however, the primary MCT in coconut oil is lauric acid. While lauric acid does not possess all of the features of the other MCTs, it does provide an array of additional benefits, such as its antimicrobial properties.
While different fat sources contain varying amounts of each type of MCT, our food sources of MCTs are primarily composed of lauric acid (with the exception of goat milk and certain other animal milk). To obtain a greater percentage of the other MCTs, incorporating supplemental fat, such as MCT oil or powder, may be more beneficial.
MCT oil is derived from the hydrolyzing of coconut oil. This occurs through esterification of these fatty acids to glycerol, leaving a higher concentration of caprylic acid (C8) and capric acid (C10) and excluding lauric acid (C12).
Concentrated forms of each particular MCT can be found. Caprylic acid (C8), or octanoic acid, is the MCT commonly wanted in a purified form. By further removing the other MCTs, we can obtain C8 on its own. Research has shown that C8 ingestion results in a greater increase in ketone production when consumed in a fasted state (20).
MCT oil can also be found in a powder form that is made through a process known as spray drying. Spray drying results in the water particles being evaporated, leaving a powdered form of MCTs. MCT powder is typically tolerated better than the oil, meaning that more can be consumed compared to the oil. Additionally, MCT powder can be used in many great ketogenic food recipes! Be careful, however, when looking for MCT powders because maltodextrin is often used as the plating source for the oil. Instead look for MCT powders that are plated on a different type of fiber!
There are a variety of different ways in which MCTs can be incorporated into your diet, and determining which source to use is dependent on your goal. Food sources, such as coconut oil, may be beneficial to include due to the various health benefits of lauric acid. MCT supplements may be better suited for those who aim to increase ketone levels. Including a variety of both would likely be an ideal situation for any ketogenic dieter.
While the isolation of MCTs from various sources is no novel strategy, it was not until recently that the safety of this approach was actually assessed. A study conducted in 2013 demonstrated that 30 grams of MCTs daily for 30 days had no adverse side effects on markers such as serum glucose, insulin, triglycerides, cholesterol, free fatty acids, body weight, or BMI (21). The safety of 1 g of MCTs per kg of body weight a day has now been established in a variety of species including humans (22).
With the current literature, it appears that MCT consumption is safe for most individuals; however, potential side effects can result from consuming MCTs in high doses. These side effects are typically gastrointestinal, such as nausea, gas, vomiting, and diarrhea. For this reason, each individual should start at a small dose to assess tolerance. In time, it is likely that your tolerance will increase, and you will be able to stomach higher amounts of MCTs! If you continue to struggle with this, MCT powders have been reported to not cause as much stomach distress as other forms. A final note to consider when cooking with MCTs is that that the smoke point is much lower compared to other commonly used cooking oils.
- MCTs are digested and result in energy production at a faster rate than other fatty acids.
- MCTs can aid in weight loss, performance, keto-adaptation, improved cognition, and the treatment of various diseases.
- MCTs are found in many natural sources as well as certain supplements.
- If looking to increase your MCT intake, consuming supplemental MCTs in the form of oil or powder is the best option.
- Side effects include gastrointestinal distress so be sure to assess tolerance and slowly titrate up.
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