Bulletproof Coffee: Does It Break a Fast?

The ketogenic diet often intersects with intermittent fasting, and bulletproof coffee sits at this crossroads. This high-fat coffee blend, typically containing grass-fed butter and MCT oil, raises questions about its compatibility with fasting states.

What Constitutes Breaking a Fast?

Nutritionally, fasting means abstaining from calorie consumption. Studies suggest that consuming over 50 kcal can trigger metabolic responses like insulin secretion (Hyde et al., 2019). A standard bulletproof coffee with 1 tbsp butter (100 kcal) and 1 tbsp MCT oil (130 kcal) exceeds this threshold.

The Ketogenic Perspective

While bulletproof coffee may technically break a fast, it aligns with ketogenic diet principles. The absence of carbohydrates means it won’t spike blood glucose significantly (Westman et al., 2008). Many find it sustains them until their first proper meal.

What This Means in Practice

In the UK, a 250g pack of Kerrygold grass-fed butter costs £2.80 at Tesco, while 500ml of MCT oil averages £15-£20. During colder months, this warming drink can replace breakfast comfortably. The NHS notes that any dietary approach should be discussed with a GP if managing health conditions.

Frequently Asked Questions

Does bulletproof coffee affect ketosis?

No. The high fat content supports ketone production without significant carbohydrate intake (Volek et al., 2008).

Can I drink it during a water fast?

Technically no, as it contains calories. But it’s compatible with fat-fasting approaches.

Will it curb morning hunger?

Yes. The fats promote satiety hormones, reducing appetite (Sumithran et al., 2013).

The Bottom Line

Bulletproof coffee provides ketogenic fats but breaks a pure fast. It serves as a transitional option for those adapting to intermittent fasting. the science of ketosis explains metabolic shifts, while time-restricted eating windows offers alternative approaches. If you’d rather not do the macro maths yourself, the Keto Dieting app does it for you on Google Play and the App Store.

Educational only — not medical advice. This article is for general information. Speak to your GP before changing your diet, especially if you have type 1 or type 2 diabetes, kidney or liver disease, are pregnant or breastfeeding, or take medication for blood pressure, cholesterol, or blood glucose.

References

Hyde PN, Sapper TN, Crabtree CD, et al. (2019). Dietary carbohydrate restriction improves metabolic syndrome independent of weight loss. JCI Insight. https://doi.org/10.1172/jci.insight.128308
Westman EC, Yancy WS, Mavropoulos JC, Marquart M, McDuffie JR (2008). The effect of a low-carbohydrate, ketogenic diet versus a low-glycemic index diet on glycemic control in type 2 diabetes mellitus. Nutrition & Metabolism. https://doi.org/10.1186/1743-7075-5-36
Volek JS, Phinney SD, Forsythe CE, et al. (2008). Carbohydrate restriction has a more favorable impact on the metabolic syndrome than a low fat diet. Lipids. https://doi.org/10.1007/s11745-008-3274-2
Sumithran P, Prendergast LA, Delbridge E, et al. (2013). Ketosis and appetite-mediating nutrients and hormones after weight loss. European Journal of Clinical Nutrition. https://doi.org/10.1038/ejcn.2013.90