Does MCT Oil Break a Fast? Butter, Cream and Calories
Does MCT oil break a fast? Yes, by the calorie definition. One tablespoon of MCT oil is 130 calories of pure fat, so it ends a strict calorie fast. It has zero carbohydrate and raises blood ketones, which is why people fasting for ketosis often keep it. Whether MCT oil "breaks" your fast depends on why you fast. The same logic applies to butter, ghee, heavy cream, half-and-half, and creamers, each at different calorie and carb counts per tablespoon.
Key Takeaways
- MCT oil (130 cal per tbsp) breaks a calorie fast. It does not break ketosis and may raise ketones, especially C8 (caprylic acid) oil.
- Butter (102 cal), ghee (115 to 120 cal), and heavy cream (51 cal) also break a calorie fast at one tablespoon.
- Bulletproof coffee, made to the brand's own recipe, is about 250 calories per cup.
- No human study has tested whether MCT oil preserves or blocks autophagy during a fast. Pages claiming otherwise are guessing.
Does MCT Oil Break a Fast? Depends on the Goal
"Breaking a fast" means different things depending on the goal. For the full breakdown, see our guide on what breaks a fast, goal by goal.
Goal 1: Calorie (clean) fast. If your rule is zero calories, then yes. One tablespoon of MCT oil is 130 calories (Nutiva label). Some people cite an informal "under 50 calories" threshold, but no clinical trial has validated a specific cutoff.
Goal 2: Ketosis. MCT oil has zero carbohydrate and is rapidly converted to ketone bodies. A tablespoon of C8 MCT oil works in your favor, not against it (see the ketone data below).
Goal 3: Insulin and autophagy. The evidence is thin. One small, old study found that a large MCT dose raised insulin transiently in children. A six-week adult trial found no change. Autophagy? No human study has measured MCT oil's effect on it.
MCT Oil, Butter and Cream: Calories per Tablespoon
All values are per one level tablespoon (about 14 to 15 mL), sourced from USDA FoodData Central and brand labels.
| Add-in | Calories | Fat (g) | Carbs (g) | Breaks a calorie fast? | Breaks ketosis? |
|---|---|---|---|---|---|
| MCT oil (C8, e.g. Bulletproof Brain Octane) | 130 | 14 | 0 | Yes | No |
| MCT oil (C8/C10 blend, e.g. Nutiva Organic) | 130 | 14 | 0 | Yes | No |
| Coconut oil | ~121 | 13.6 | 0 | Yes | No |
| Butter, salted | ~102 | 11.5 | <0.1 | Yes | No |
| Ghee, clarified butter | ~115 to 120 | ~13 | 0 | Yes | No |
| Heavy whipping cream | ~51 | 5.4 | 0.4 | Yes (borderline) | No |
| Half-and-half | ~20 | 1.7 | 0.6 | Debatable | No |
| Whole milk | ~9 | 0.5 | 0.7 | Likely no | Trace carbs |
| Coffee mate Original (liquid) | 20 | 1 | 2 | Debatable | Corn syrup solids |
Sources: USDA FDC 173410 (butter), 170859 (cream), 171255 (half-and-half), 171412 (coconut oil). Labels: Bulletproof recipe, Nutiva MCT, Coffee mate.
Bulletproof coffee, per the brand's own recipe: 1 tbsp Brain Octane C8 MCT oil + 1 tbsp grass-fed ghee + 8 to 12 oz brewed coffee = 250 calories, 27 g fat (Bulletproof recipe page).
Does MCT Oil Kick You Out of Ketosis? The Ketone Studies
The opposite. C8 MCT oil is one of the strongest dietary ketone boosters tested in humans.
In a crossover study of 9 healthy adults, Vandenberghe et al. (2017) gave two 20 mL doses of different oils. Pure C8 (tricaprylin) produced the highest day-long ketone response (+295 µmol/L above control). Coconut oil peaked at about 25% of C8's level (PMID 29955698).
St-Pierre et al. (2019) compared C8, C10, and C12 directly. C8 was roughly 3x more ketogenic than C10 and about 6x more than C12. Ketone response was about 2-fold higher when taken without a meal (PMID 31058159).
Both studies used 20 mL doses in small samples. Separately, caffeine alone at breakfast (2.5 and 5.0 mg/kg) raised ketone production by 88% and 116% in a 10-person study (PMID 28177691). Whether caffeine amplifies MCT's ketogenic effect hasn't been tested.
Bottom line for ketosis: C8 oil taken without food raises ketones the most. Regular coconut oil is a weak substitute. See also: MCT and other fats for the brain and ketones and focus during a fast.
Does MCT Oil Spike Insulin? What Little Data Exists
Two studies, very different designs, mixed signals.
Valls et al. (1978) gave 10 healthy children a large dose (1.5 g/kg) of MCT. Insulin rose from 30 to 90 minutes; glucose did not change. Thomas et al. (2019) fed 22 adults without diabetes 30 g of MCT daily for six weeks. Fasting glucose, insulin, and insulin sensitivity showed no significant changes (PMID 31869355).
Neither study tested a tablespoon in coffee during a 16-hour fast. The insulin response is probably small, but "probably" is not data.
Autophagy? No human trial has measured MCT oil's effect on autophagy markers during fasting. If a page says "autophagy preserved," ask for the citation. There isn't one.
Does Heavy Cream, Half-and-Half or Creamer Break a Fast?
By the numbers in the table above: one tablespoon of heavy cream is about 51 calories with 0.4 g carbs. Half-and-half is about 20 calories with 0.6 g carbs. Coffee mate Original is 20 calories but contains corn syrup solids as its second ingredient, which means some of those calories come from sugar, not fat.
A splash of heavy cream (a teaspoon or two) lands around 17 to 34 calories. Some intermittent fasters call this acceptable; strict clean fasters don't. Dairy also carries lactose and some protein, both of which can prompt a small insulin response. Flavored creamers add sugar or corn syrup on top of that.
For more on whether black coffee breaks a fast, we have a separate breakdown.
Does Bulletproof Coffee Break a Fast?
By any calorie-based definition, yes. Bulletproof's own recipe totals 250 calories and 27 g of fat per cup (recipe page). That is not a fast. It is a fat-only meal.
Some people call this "dirty fasting," restricting carbs and protein but allowing pure fat. That is a personal protocol, not a tested one. No trial has compared "dirty fasting" with bulletproof coffee to a true zero-calorie fast.
Bulletproof recommends new users start at 1 teaspoon of MCT oil, and Nutiva's label warns that excess may cause stomach discomfort. Titrate up.
What to Use Instead If You Want a Clean Fast
Zero calories in the fasting window means a short list:
- Black coffee (2 to 5 calories per cup, negligible). See whether black coffee breaks a fast.
- Plain tea, black or green, no sweetener. See plain tea during a fast.
- Water, still or sparkling.
- Unflavored electrolytes (sodium, potassium, magnesium). See electrolytes while fasting.
Decide the Goal First, Then the Spoon
MCT oil, butter, cream, and creamers all contain calories. Whether those calories "break" your fast depends on what you are trying to accomplish. Zero-calorie goal? A tablespoon of anything on this list ends it. Ketosis goal? C8 MCT oil helps, not hurts. Insulin or autophagy goal? The data is too thin for a confident answer, and anyone giving one is selling something.
Pick your goal. Then check the table.
Frequently Asked Questions
Does MCT oil break a fast?
By calorie count, yes. One tablespoon is 130 calories, ending a zero-calorie (clean) fast. It does not break ketosis: MCT oil has zero carbs and raises blood ketones, so people fasting for ketosis often include it. The answer depends on your goal.
Does MCT oil kick you out of ketosis?
No. C8 MCT oil is one of the most ketogenic fats tested. In a crossover of 9 adults, C8 produced the highest plasma ketone response of any oil tested (PMID 29955698). It deepens ketosis rather than breaking it. For zero-carb caffeine options for keto, see our guide.
Does heavy cream break a fast?
One tablespoon is about 51 calories and 0.4 g carbs (USDA FDC 170859). A full tablespoon breaks a strict calorie fast. A smaller splash (1 to 2 teaspoons, 17 to 34 calories) is a gray zone some fasters accept and others don't.
Does butter break a fast?
Yes. One tablespoon of salted butter is about 102 calories and 11.5 g of fat (USDA FDC 173410). That is well above any informal calorie threshold. Butter has almost zero carbs, so it does not disrupt ketosis.
Does bulletproof coffee break intermittent fasting?
Yes by any calorie standard. The brand's own recipe totals 250 calories and 27 g fat. That replaces a fast with a fat-only meal. "Dirty fasting" is a personal label, not a clinical protocol.
Does MCT oil break a fast for autophagy?
Unknown. No human study has measured MCT oil's effect on autophagy markers during a fast. Most autophagy data comes from cell or animal models. Any page claiming MCT oil "preserves autophagy" is extrapolating beyond the evidence.
Caffeine Without the 250-Calorie Cup
Many people add MCT oil or butter to coffee because they want a long, steady morning. The cost is 130 to 250 calories that end a calorie fast before noon.
If the goal is a zero-calorie fast plus caffeine that lasts, the math points away from the cup. Roon is a zero-calorie, zero-sugar sublingual pouch (it does contain sucralose) with 80 mg caffeine and 60 mg L-theanine. A 2025 meta-analysis of 50 RCTs found L-theanine plus caffeine improved attention-switching accuracy at hour two (SMD 0.33, 95% CI 0.13 to 0.54; lead author's PhD funded by Lipton). Why 6 to 8 hours from 80 mg? Methylliberine (Dynamine) slows caffeine clearance. In an n=12 double-blind crossover, 100 mg methylliberine + 150 mg caffeine cut clearance from 41.9 to 17.1 L/hr and extended half-life from 7.2 to 15 hours, no higher peak. That study used 4x Roon's methylliberine and ~2x its caffeine, so the mechanism is directionally the same, not identical. Roon's felt window is 6 to 8 hours. Stop at least 8 hours before bed.
Roon is not a ketone source, not a meal replacement, and makes no fasting-physiology claim beyond having zero calories. From $9.16 per tin on a 12-tin subscription ($0.61 per pouch). If you want the duration without the cup, try Roon.
Related from Roon
- Does Coffee Break a Fast?
- What Breaks a Fast?
- Intermittent Fasting and Focus: The Ketone Connection
- Keto-Friendly Energy Drinks
Written by Roon Team
