Medium-chain triglycerides (MCTs) have become increasingly popular as people are learning more about the health benefits of nutritional ketosis, which is achieved by replacing net carbohydrates (total carbs minus fiber) with high amounts of healthy fats and moderate amounts of high quality protein.
Some of the health benefits of coconut oil relate to the MCTs in the oil. But MCT oil is a more concentrated source, so it tends to be more appropriate for clinical uses, which include: 
- Appetite reduction and weight loss [2,3]
- Improved cognitive and neurological function with possible implications in neurodegerative diseases
- Increased energy levels and improved athletic performance
- Improved mitochondrial function and subsequent reduced risk for diseases such as atherosclerosis, diabetes, cancer, cardiovascular disease, autoimmune diseases and epilepsy 
- As part of a specialized dietary therapy for the treatment of epilepsy
- Prevention of non-alcoholic fatty liver disease (NAFLD) 
The disastrous "low-fat diet" dogma of the last half century has led to a devastating drop in most people's intake of healthy saturated fats, including MCTs, as most people have bought into the erroneous assumption that saturated fats are unhealthy and will raise their risk of heart disease.
Besides coconuts, coconut oil and palm kernel oil, small amounts of MCT can be found in butter and other high-fat dairy products from grass-fed cows and goats.
Be sure not to confuse the extremely unhealthy industrial versions of coconut and palm oils (which are historically used as hydrogenated oils in industrial baked goods) with organic, virgin and unrefined oils available as "health foods."
MCTs get their name from their chemical structure. Fats consist of chains of carbon molecules connected to hydrogen atoms. Short-chain fats have six carbons or less.
Medium-chain fats contain between six and 12 carbons, while long-chained fats, such as the omega-3 fats docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), have 13 to 21 carbons.
Four Types of MCTs
MCTs can be divided into four groups based on their carbon length: 
- 6 carbons (C6), caproic acid
- 8 carbons (C8), caprylic acid
- 10 carbons (C10), capric acid
- 12 carbons (C12), lauric acid
I recently wrote about how a novel ketone ester drink may help boost performance in professional athletes, but while ketone supplements are still in development, your best bet at the moment is to use MCTs found in foods and supplements, which your body will then convert to ketones.
Most commercial brands of MCT oil contain close to a 50/50 combination of C8 and C10 fats. My personal preference, even though it is more expensive, is straight C8 (caprylic acid), as it converts to ketones far more rapidly than do C10 fats, and may be easier on your digestion.
Coconut oil provides a mix of all the medium-chain fats, including C6, C8, C10 and C12 fats, the latter of which (lauric acid) makes up over 40 percent of the fat in coconut oil. (The exception is FRACTIONATED coconut oil, which contains primarily C8 and C10. )
There are benefits to all of these fatty acids. However, caprylic and capric fatty acids increase ketone levels far more efficiently.
Also, while lauric acid is technically an MCT, its longer carbon chain means it does not always have the same biological activity as the shorter chained ones. In fact, C12 can behave more like long-chain fatty acids (LCTs), which are less efficiently broken down into ketones.
As a result, C12 is less potent when it comes to curbing hunger and promoting brain health. For these benefits, you want C8 and C10. Lauric acid is most well-known for its antibacterial, antimicrobial and antiviral properties.
The shorter-chained MCTs, on the other hand, are more readily converted into ketones, which are an excellent mitochondrial fuel. Ketones also help suppress ghrelin (a.k.a. the hunger hormone) and enhance another hormone that signals your brain when you're full.
Why Take MCT Oil?
Your body processes MCTs differently from the long-chain fats in your diet. Normally, a fat taken into your body must be mixed with bile released from your gallbladder and acted on by pancreatic enzymes to break it down in your digestive system.
MCTs don't need bile or pancreatic enzymes. Once they reach your intestine, they diffuse through your intestinal membrane into your bloodstream and are transported directly to your liver, which naturally converts the oil into ketones.
Your liver then releases the ketones back into your bloodstream, where they are transported throughout your body. They can even pass the blood-brain barrier to supply your brain with energy. MCTs also have a thermogenic effect, which has a positive effect on your metabolism. 
For these reasons, MCTs are readily used by your body for energy rather than being stored as fat. MCTs are also helpful for ridding your gut of harmful microorganisms like pathogenic bacteria, viruses, fungi and parasites. Like coconut oil, MCTs also have antioxidant and anti-inflammatory properties.
MCT oil (either straight MCT or coconut oil) may be consumed every day. One of the challenges with MCT oils is that if you consume high amounts initially before you develop tolerance to them, they can cause loose stools and gastrointestinal (GI) side effects.
I recommend taking no more than 1 teaspoon of MCT oil to start. Have it at the same time as another fat, for example, with a handful of nuts, with ghee in your coffee or as one of the oils in your salad dressing. Once your tolerance increases, you can slowly increase that amount to 4 tablespoons of MCT oil per day.
If you stop taking MCT oil for a while and then restart, begin with a small amount again to allow your digestive system to readjust.
That said, MCT oil is often more easily digested by those struggling to digest other types of fat, such as those with malabsorption, leaky gut, Crohn's disease or gallbladder impairment (such as an infection or if you had your gallbladder removed).
One of the ways you can improve your tolerance is by using the powdered form in shakes or home baked keto muffins or breads.
How MCT Oil May Aid Weight Loss
Animal and human studies have demonstrated that MCTs enhance thermogenesis and fat oxidation, thereby suppressing the deposition and accumulation of body fat.  In other words, they have a heating effect, and your body can readily use ketones as fuel for energy in lieu of carbs.
By helping your body burn fat and produce more ketones, MCTs provide you with effects that are very similar to those you would reap from a ketogenic diet, but without having to reduce your net carbs to as drastically low levels as you would on a ketogenic diet. Here's a small sampling of studies looking at MCTs' impact on weight:
- One three-month-long, double-blind and controlled study  found that long-term consumption of MCTs helped otherwise healthy adults lose significantly more subcutaneous body fat than those who took LCTs. All subjects consumed 60 grams of total fat per day. The difference was the type of fat (MCT versus LCT). The energy, protein and carbohydrate levels were otherwise similar. According to the authors, "These results suggest that the MCT diet may reduce body weight and fat in individuals (BMI > or = 23 kg/m(2) more than the LCT diet."
- A 2015 meta-analysis  of 13 randomized controlled trials found that, compared to LCTs, MCTs more effectively decreased body weight, waist circumference, hip circumference, total body fat, total subcutaneous fat and visceral fat. There was no difference in blood lipid levels between the two fats. According to the authors: "Replacement of LCTs with MCTs in the diet could potentially induce modest reductions in body weight and composition without adversely affecting lipid profiles."
- Other research suggests MCTs help with weight loss by reducing your appetite. As reported by Mental Health Daily:  "Some scientists speculate that MCT acts on various hormones such as: cholecystokinin, gastric inhibitory peptide, pancreatic polypeptide, peptide YY and neurotensin. The precise mechanism of action of MCTs remains unknown, but it is known to induce satiety and reduced appetite compared to [LCTs]."
That said, in most studies the effect on weight loss has been small — perhaps too small to make a significant impact on its own. As noted by Paleo Leap: 
"The authors … use kilojoules to measure energy instead of calories, but when you convert the units, you'll see that few of the studies showed a benefit relevant to the real world. For example, one study found that 5 grams of MCT oil did indeed raise the metabolic rate of healthy men … by 11 calories a day … [Y]ou could burn more calories than that by walking for [five] minutes, or jumping rope slowly for [two] minutes."It's important to realize that MCT oil will not produce weight loss miracles all on its own. However, it is an excellent addition to an otherwise healthy diet. Moreover, many consider MCTs "the ultimate ketogenic fat," as it allows you to eat slightly more net carbs while still staying in nutritional ketosis. Without MCTs, you'd have to cut carbs more drastically in order to maintain ketosis.
If you're serious about losing weight, review and implement the recommendations in my updated Nutrition Plan. It will guide you step-by-step. MCT oil is a healthy fat that I recommend using in addition to other healthy fats, which include:
- Olives and olive oil (make sure it's third party-certified, as 80 percent of olive oils are adulterated with vegetable oils. Also avoid cooking with olive oil. Use it cold.)
- Raw nuts, such as macadamia and pecans
- Grass-fed meats
- Raw cacao butter
- Coconuts and coconut oil (excellent for cooking as it can withstand higher temperatures without oxidizing)
- Seeds like black sesame, cumin, pumpkin and hemp seeds
- Lard and tallow (excellent for cooking)
- Organic-pastured egg yolks
- Butter made from raw grass-fed organic milk
- Ghee (clarified butter)
- Animal-based omega-3 fat such as krill oil and small fatty fish like sardines and anchovies
MCTs are a superior brain fuel, converting to ketones within minutes of ingestion. Therapeutic levels of MCTs have been studied at 20 grams per day. This is the amount indicated for protection against degenerative neurological diseases, or as a treatment for an already established case.  As noted by Mental Health Daily: 
"In small scale human trials,  MCT supplementation boosted cognition in individuals with cognitive impairment and mild forms of Alzheimer's disease after just a single dose. While not everyone improved from the MCT treatment, those with certain genetics experienced notable improvement."Ketones appear to be the preferred source of energy for the brain in people affected by diabetes, Alzheimer's, Parkinson's and maybe even ALS, because in these diseases, certain neurons have become insulin resistant or have lost the ability to efficiently utilize glucose. As a result, neurons slowly die off.
The introduction of ketones may rescue these neurons and they may still be able to survive and thrive. In multiple studies, ketones have been shown to be both neurotherapeutic and neuroprotective. They also appear to lower markers of systemic inflammation, such as IL-6 and others.
Your heart health can also derive great benefit from MCTs. Human studies have shown MCTs help lower total lipid levels and improve cardiovascular health. For example, people who regularly consume coconut oil have a lower incidence of heart attack compared to those who do not consume coconut oil — an effect attributed to the MCT in the coconut.
A 1991 study  found that palm kernel oil was even more effective for lowering serum cholesterol than coconut oil, dairy and animal fats. Palm kernel oil also helped raise beneficial HDL cholesterol.
In 2010, researchers published findings showing MCTs help lower your risk of developing metabolic syndrome,  which includes a cluster of symptoms such as abdominal obesity, high blood pressure and insulin resistance. Unlike carbohydrates, ketones don't stimulate a surge in insulin. Another benefit is that they don't need insulin to help them cross cell membranes, including neuronal membranes. Instead, they use protein transporters, which allow them to enter cells that have become insulin resistant.
How Much MCT Do You Need?
While optimal dosing will vary from person to person, depending on your health status, energy needs and what your GI tract can tolerate, here are some general guidelines to consider:
- Start with 1 teaspoon and work your way up, adding 1 teaspoon at a time over the course of a few weeks. If you experience GI distress or diarrhea, cut back. While it's not harmful to overdose on MCT, your body will rid itself of the excess by causing diarrhea, so don't overdo it.
- Studies suggest an ideal ketone concentration for maximum hunger suppression and fat burning is 0.48 millimole per liter (mmol/L).  Ketone measurements can be done through urine, breath or blood testing. Blood testing is the most expensive but also the most accurate and easy to test with home meters and strips. Measure your ketones about one hour after taking your MCT oil, and slowly build up your dose until you reach 0.48 mmol/L.
- Alternatively, simply raise the dose (slowly) until you notice you're no longer as hungry as you used to be.
- For supplementation in neurological diseases like Alzheimer's, studies have found beneficial effects using a daily dose of 20 grams (about 4 teaspoons) of MCT oil.
Remember, coconut oil is predominantly lauric acid, which has many benefits, including antimicrobial. However, it does not convert as efficiently into ketones and therefore does not contribute much of an energy boost. Nor does it suppress hunger or help feed your brain the way C8 and C10 do. MCT oil is typically tasteless and odorless, so it can easily be added to a wide variety of dishes and beverages, from salad dressing to smoothies and vegetable juices.