A fractionated fat containing medium-chain triglycerides, usually caprylic acid (C8) and capric acid (C10), made from coconut or palm kernel oil. Medium-chain fatty acids are absorbed through the portal vein and reach the liver directly rather than travelling as chylomicrons.
MCTs have a genuinely distinctive metabolic route, and that route is why they were used in clinical nutrition for fat malabsorption long before anyone put them in coffee. The weight-loss case is much weaker than the marketing suggests: meta-analyses comparing MCT with long-chain fat report roughly half a kilogram of difference over about ten weeks, in trials that are small, short and often industry-funded, and that difference does not obviously persist. MCTs also supply the same 8–9 kcal per gram as any other fat, which is the fact the marketing works hardest to obscure.
Sold as
Liquid oil, Powder (often with acacia or maltodextrin carrier), Softgel
Standardised to
C8 and C10 percentage; "MCT oil" may be anything from pure C8 to a C8/C10/C12 blend — a product without this marker may not resemble what was studied.
Regulation: Sold as a food or dietary supplement with no pre-market efficacy review. Medium-chain triglycerides are separately used in medical nutrition products for fat malabsorption, where the evidence is much stronger and the context is clinical.
What the research used
The amounts, forms and durations published trials of MCT oil actually administered.
These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.
Studied for Body composition and energy intake trials
Trials substitute MCT for other dietary fat rather than adding it. Pooled differences are around 0.5 kg over roughly ten weeks, and several trials were funded by MCT producers.
Studied for Raising blood ketones
10–20 g
Moderate
C8-rich MCT, single dose · Acute, peaking 1–2 hours after ingestion
The ketone rise is real, dose-dependent and short-lived. Whether a transient rise in beta-hydroxybutyrate produces any measurable benefit is a separate and much less settled question.
This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.
When it was taken
Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.
None of the timings below were directly compared in a trial. They reflect how the research happened to dose, or what the pharmacology implies — which is not the same as a timing being better.
🕐Any time
Not enough
No timing comparison has established a difference in outcome. What is well established is that starting at a small dose and increasing gradually is what avoids the cramping and diarrhoea that a first tablespoon commonly causes.
Timing was not directly compared. This reflects convention or how the compound behaves in the body, not a trial showing this window works better.
The evidence in depth
Best supported: Limited
What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.
Meta-analyses of MCT substituted for long-chain fat report small reductions in body weight and fat mass — around half a kilogram over about ten weeks. The trials are short, small and often industry-funded, and MCT adds the same energy as any other fat when it is added rather than substituted.
What may be going on: Medium-chain fatty acids are absorbed via the portal vein and oxidised rapidly in the liver, with a modest increase in energy expenditure and ketone production compared with long-chain fats.
Limited evidence. Early human work, or mostly lab and animal research.
Some short trials report reduced energy intake at a subsequent meal after MCT compared with long-chain fat, plausibly through ketone signalling. Results are inconsistent and the effect has not been shown to persist over weeks.
Limited evidence. Early human work, or mostly lab and animal research.
MCT raises blood ketones, which the brain can use as fuel, and small trials in mild cognitive impairment have reported changes on some tests in subgroups defined after the fact. There is not enough dependable human research to call this established.
Not enough evidence. Not enough human research to say anything useful yet.
Randomised controlled trial · Alzheimer's & dementia : the journal of the Alzheimer's Association · 2021 · PMID 33103819
Deep research mode adds each paper’s own conclusion and stated limitations.
Things to know
Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.
Worth knowing
Ketoacidosis risk in diabetes
Interacts withSGLT2 inhibitors, insulin
MCT raises ketone production. In people with type 1 diabetes, or on SGLT2 inhibitors which themselves raise ketogenesis, this is not a neutral effect and should be discussed with a clinician.
Worth knowing
Contraindicated in some liver disease
Because medium-chain fatty acids go straight to the liver via the portal vein, MCT is avoided in hepatic encephalopathy and advanced cirrhosis, where rapid delivery of fatty acids and ketone production can be harmful.
Too much
Cramping, nausea and diarrhoea
The dose-limiting effect for most people, and it appears quickly at a tablespoon or more in someone unaccustomed to it. Gradual introduction is the standard approach; taking it on an empty stomach makes it worse.
Worth knowing
It is still fat, at 8–9 kcal per gram
MCT added on top of an existing diet adds energy. The trials that found any body-composition benefit substituted it for other fat rather than adding it to coffee.
In the food catalogue
The whole-food form, where one exists. The evidence for a concentrated extract rarely transfers to the food, or the other way round — these are cross-links, not equivalents.