Benefits
Raises blood ketones more than other medium-chain fats
In crossover studies of healthy adults, two 20 mL doses of pure C8 oil gave the largest ketone rise of the oils tested: about three times that of C10 and six times that of C12, well above coconut oil, and about a fifth to a quarter above standard C8 and C10 MCT oil. A separate study in 7 adults also found C8 the most ketogenic oil. These are blood markers measured over hours, not health outcomes.
Ketone response depends on the carbohydrate eaten with it
In 15 healthy adults aged 65 to 73, 20 g of C8 raised blood ketones, but adding 50 g of glucose lowered the average level from 0.45 to 0.28 mmol/L (0.18 with sunflower oil). In 11 young women, the ketone rise from C8 was no longer significant at the highest glucose dose. A review of 7 trials agreed that carbohydrate blunts it. In another study, ketone responses to medium-chain oils were about twice as high when taken without a meal.
Fat burning during light exercise in sedentary adults
In a randomized crossover trial in sedentary adults in their 40s and 50s, 6 g a day of C8-rich MCT for 14 days raised fat burning during light cycling compared with no MCT, and power output at the ventilation threshold rose with both C8-rich and C10-rich MCT. The trial was run by staff of an MCT oil maker and measured fuel use, not weight or fitness over time.
Hunger and alertness after C8 in coffee
In a small double-blind study, 7 healthy young adults drank 10 mL of C8, C10, a C8 and C10 blend, or coconut oil in coffee, with or without caffeine. C8 gave the highest ketone rise, yet hunger climbed and fullness fell over 4 hours with every drink, and participants did not report more energy. The authors could not confirm the claims made for this kind of coffee.
Effects on Candida yeast in lab cultures
In lab cultures, caprylic acid blocked Candida albicans from switching to its thread (hyphal) form, sticking to surfaces and forming biofilms, and it killed the yeast at high concentrations, though it needed twice the concentration that capric acid (C10) did. No human trial has tested caprylic acid capsules for yeast in the gut, and a yeast infection needs medical care.
Mechanism of action
Fast conversion to ketones in the liver
Medium-chain fatty acids are handled differently from long-chain fats and are quickly turned into ketones by the liver. After a dose of C8 oil, plasma octanoate rose and the ketone rise tracked it; oils that contained less C8, or diluted it with C10, produced smaller ketone responses in healthy adults.
Carbohydrate acts as a brake
When glucose is taken with C8, ketone production falls. In healthy volunteers given a fixed C8 dose, the ketone rise shrank as the glucose dose grew, and raising C8 and glucose together restored it. A pooled review of 7 trials found the same pattern, with varied study designs.
Supplies the fatty acid that activates ghrelin
Ghrelin, a stomach hormone that stimulates appetite, becomes active only when an octanoic acid chain is attached to it, and a review suggests dietary C8 can supply that chain. In a small study in underweight patients with chronic lung disease, an octanoic acid-rich formula raised active ghrelin, the opposite of the appetite suppression often claimed for MCT.
Disrupts yeast growth programs in lab cultures
In cultured Candida albicans, caprylic acid lowered the activity of genes that drive the switch to the thread form, raised genes that hold the yeast in its round form, and arrested the cell cycle. These are test-tube findings and do not show what happens in the human gut.
Clinical trials
Crossover metabolic study comparing two 20 mL doses of coconut oil, standard MCT oil (55% C8, 35% C10), pure C8, pure C10, or 50:50 blends of coconut oil with C8 or MCT oil, each emulsified in skim milk, with a milk-only control over 8 hours. (Vandenberghe et al. 2017, Curr Dev Nutr)
9 healthy adults, mean age 34.
C8 was the most ketogenic oil, raising plasma ketones by a day-long average of about 295 µmol/L above control, with 0 to 4 h and 4 to 8 h ketone areas 813% and 870% above control. Coconut oil's ketone peak was about 25% of the C8 peak. No significant digestive side effects were reported. A blood marker over one day, not a health outcome.
Crossover metabolic study day: a 20 mL dose of tricaprylin (C8), tricaprin (C10), trilaurin (C12) or a C8 and C10 blend with breakfast, and a second dose 4 hours later without a meal. (St-Pierre et al. 2019, Front Nutr)
9 healthy adults (7 men, 2 women); 8 completed the C10 test.
C8 was about three times more ketogenic than C10 and about six times more than C12, and the ketone rise was related to the rise in plasma octanoate. Ketone responses were about twice as high when the dose was taken without a meal. An 8-hour laboratory test; no clinical outcomes were measured.
Randomized 6-arm crossover after a 12-hour fast: sunflower oil (control), C8 20 g (with 10 g sunflower oil), C8 plus 50 g glucose, coconut oil 30 g, coconut oil plus glucose, or C8 plus coconut oil, each with coffee and cream; ketones measured for 4 hours. (Norgren et al. 2020, Front Nutr)
15 healthy adults aged 65 to 73 (53% women) in Sweden.
Mean beta-hydroxybutyrate over 4 hours was 0.45 mmol/L with C8 versus 0.18 with sunflower oil and 0.22 with coconut oil; coconut oil did not differ significantly from sunflower oil. Adding glucose to C8 lowered it to 0.28. After the C8 arm, 87% reported no discomfort and 13% minor discomfort. One participant dropped out after severe diarrhea following the coconut oil arm.
Controlled, double-blind study of 10 interventions: 10 mL of C8, C10, a 50:50 C8 and C10 blend, or coconut oil in decaffeinated coffee, with or without 150 mg caffeine, plus coffee-only controls with and without caffeine; ketones and glucose measured for 4 hours. (Baumeister et al. 2021, J Nutr Metab)
7 healthy young adults.
C8 raised ketones the most, the effect fell with longer chain length, and caffeine added to it. Hunger rose and fullness fell during every intervention, and participants reported no extra energy; the authors could not confirm the effects claimed for MCT coffee. Abdominal pain and nausea were among the most common side effects and occurred mostly with the oil drinks. Very small study.
Randomized, controlled, double-blind crossover: a fixed dose of tricaprylin (99% C8, 0.2 g/kg body weight) with rising glucose doses (0.2 to 0.6 g/kg), plus arms raising C8 and glucose together, after an overnight fast. (Frenser et al. 2026, Sci Rep)
11 healthy young women, mean age 22.5.
C8 raised beta-hydroxybutyrate above control at the low and medium glucose doses but not at the highest. Ketones fell as glucose rose at a fixed C8 dose and rose when both were increased together. No dose-dependent side effects occurred. A short test of a blood marker.
Randomized crossover: 0 g MCT, 6 g/day octanoic acid-rich MCT, or 6 g/day decanoic acid-rich MCT for 14 days each with 14-day washouts, then a cycling test. Most authors work for MCT maker The Nisshin OilliO Group. (Nosaka et al. 2020, Lipids)
Sedentary adults in their 40s and 50s in Japan.
Cumulative fat oxidation during 20 W fixed-load cycling was higher with C8-rich MCT than with no MCT. Power output at the ventilation threshold was higher with both C8-rich and C10-rich MCT. In a subgroup analysis, maximal fat oxidation and oxygen uptake were higher with both MCTs in the older participants. Fuel use in a lab test; no weight or long-term fitness outcomes.