The Bulletproof Coffee Dilemma: Intermittent Fasting Friend or Foe?

does bulletproof coffee break a fast

What is Bulletproof Coffee?

Bulletproof Coffee is a high-fat coffee drink that has become popular among followers of low-carb, high-fat diets. It was created in 2004 by Dave Asprey, founder of the Bulletproof brand.

The signature Bulletproof Coffee recipe contains just 2 main ingredients:

– Brewed coffee – Typically a light or medium roast coffee is used. Dark roasts are avoided since they tend to be higher in bitter compounds.

– Grass-fed butter – About 1-2 tablespoons of unsalted butter from grass-fed cows provide a source of healthy fats.

– MCT oil – 1-2 tablespoons of MCT (medium chain triglyceride) oil is also added. This is a type of easily digested saturated fat.

Unlike regular black coffee, Bulletproof Coffee contains a significant amount of fat, which transforms it into a filling, high-calorie beverage.

Bulletproof Coffee was created based on the idea that starting your day with healthy fats provides lasting energy and helps your body burn fat more efficiently. The concept of adding butter and MCT oil to coffee was unique at the time it was introduced.

The key difference between regular coffee and Bulletproof coffee is the addition of fats, which reduces its bitterness and provides fat-soluble nutrients. Bulletproof Coffee is meant to replace breakfast, rather than just accompany it.

Understanding Fasting

Fasting is the practice of abstaining from food and beverages (except for water) for a set period of time. There are several different types of fasting:

  • Intermittent fasting: Cycling between periods of fasting and eating. Common approaches include 16/8 (fasting for 16 hours, eating during an 8 hour window) or 5:2 (eating normally 5 days per week, fasting or restricting calories 2 days).
  • Alternate day fasting:Fasting every other day. On fasting days, some consume zero or very few calories.
  • Time-restricted fasting:Limiting eating to a specific number of hours per day, like only 8am-6pm.
  • Prolonged fasting:Fasting for longer periods, like 24-48 hours. Should only be done occasionally.

Benefits of fasting may include:

  • Weight loss and fat burning
  • Reduced inflammation
  • Improved cardiovascular health
  • Increased insulin sensitivity
  • Cellular repair
  • Longevity

Fasting plays an important role in diets like:**

  • Keto – Fasting can help initiate and maintain ketosis. Many pair keto with intermittent fasting.
  • Paleo – Intermittent fasting aligns with a Paleo approach as hunter-gatherers likely experienced periods of fasting.
  • Low carb – Fasting lowers blood sugar and insulin levels, complementing a low carb diet.

Does Bulletproof Coffee Break a Fast?

There is an ongoing debate about whether drinking bulletproof coffee breaks your fast or not. Some argue that the high-fat content of bulletproof coffee triggers digestive processes that break the fasted state. Others claim that the unique composition of bulletproof coffee keeps you in a fasted state and enhances the benefits of intermittent fasting. Let’s examine the evidence on both sides of this issue:

Arguments That Bulletproof Coffee Breaks a Fast

  1. Contains calories that could spike insulin – Bulletproof coffee has a significant amount of calories, anywhere from 200-500 calories per serving depending on ingredients and recipe. Consuming calories from fat, protein or carbs during the fasting window could stimulate insulin secretion and take you out of the fasted state.
  2. Triggers digestive processes – Even though bulletproof coffee does not contain carbs, the presence of fat and protein can trigger digestive processes like the release of bile from the gallbladder and gastric secretions in the stomach. This could potentially break the fast.
  3. Not technically “fasting” – Some fasting purists argue that anything besides plain water and black coffee would break a fast, since the body needs to metabolize and digest additional ingredients. This means bulletproof coffee cannot be considered true “fasting”.

Arguments That Bulletproof Coffee Does Not Break a Fast

  1. No carbs to spike insulin – Bulletproof coffee only contains fats and proteins, with no carbs. This means it does not cause insulin or glucose spikes that break ketosis. The lack of carbs helps maintain the fasted state.
  2. Ketogenic friendly – The high fat content of bulletproof coffee helps sustain ketosis and burn fats for fuel. This is aligned with the goal of fasting. MCT oil in particular may support ketosis.
  3. Suppresses appetite – Many find that bulletproof coffee suppresses hunger and cravings, allowing them to more comfortably extend their fasting windows. This enhances the benefits of fasting.

Expert Opinions

Expert opinions are mixed on whether bulletproof coffee breaks a fast. Some notable perspectives:

  • Dr. Rhonda Patrick believes a true fast involves no calories. She cautions that coffee creamers could activate mTOR pathways.
  • Dr. Jason Fung considers small amounts of milk or cream okay during fasts, but suggests limiting bulletproof coffee to once per day.
  • Certified nutritionist Dr. Kellyann Petrucci allows 1-2 cups of bulletproof coffee while fasting. She focuses on controlling insulin levels.
  • Dave Asprey, founder of Bulletproof, maintains that bulletproof coffee does not break a fast since it’s very low in carbs and sustains ketosis.

The Science

There is limited research specifically on bulletproof coffee and fasting. However, some studies give clues regarding the potential impact:

  •  An insulin index study found that whole milk does not produce a substantial insulin response. Butter had minimal impact as well. This suggests small amounts of dairy may not spike insulin much.
  • Research indicates that MCT oil and coconut oil help support ketone production and fat burning, aligning with fasting goals. However, effects may vary by individual.
  • One study showed caffeine may enhance metabolic rate and fat burning if consumed during fasts. This indicates coffee may provide synergistic effects.

In summary, the limited evidence available suggests that reasonable intakes of bulletproof coffee are unlikely to sabotage fasts. However, individual factors like insulin sensitivity may alter responses. Moderation and self-experimentation are advised.

Impact on Ketosis and Fat Burning

Drinking bulletproof coffee while fasting can have varying effects on ketosis and fat burning, depending on the individual. Here’s an overview of the potential impact:

Effect on Ketone Levels

Bulletproof coffee contains medium chain triglycerides (MCTs) from coconut oil, which may increase ketone production and levels. MCTs are readily converted to ketones by the liver. However, the impact can vary – some people report heightened ketosis with bulletproof coffee while fasting, while others don’t notice a significant difference.

The butter in bulletproof coffee may slightly reduce ketosis. Dairy proteins and fat can spike insulin minimally, which inhibits ketone production. Overall though, bulletproof coffee likely elevates ketones for most people during fasting.

Fat Burning Capabilities

By providing fats for energy, bulletproof coffee can preserve muscle mass and enhance fat burning capabilities during the fasted state. The fats from MCT oil and butter provide fuel for the body and brain, allowing stored body fat to be used for energy.

However, too much dietary fat can slow down fat metabolism. There’s debate around whether bulletproof coffee prolongs the switch to fat-burning mode. It likely depends on the individual and amount consumed. More research is needed on the effects.

Insulin Response

Bulletproof coffee provokes a very small insulin response compared to meals with protein or carbohydrates. However, some dairy proteins and fat may stimulate insulin minimally.

For most people, bulletproof coffee consumed during fasting will keep insulin levels low. But individuals with high insulin resistance may need to avoid it to prevent insulin spikes. Consulting a doctor is advised, especially for those with conditions like diabetes.

Overall, bulletproof coffee supports ketosis and fat burning for most people during fasting periods. But effects can vary based on the individual. Starting slowly and monitoring your body’s response is recommended.

Potential Benefits of Bulletproof Coffee

Many people report experiencing several benefits from drinking bulletproof coffee during a fast. Here are some of the main potential advantages:

Improved Mental Clarity

The combination of caffeine and healthy fats in bulletproof coffee may help boost focus and concentration. The caffeine provides a stimulant effect, while the fats help curb hunger that can distract from mental tasks. Some people find this leads to improved productivity and cognitive function when fasting.

Increased and Sustained Energy

By providing a dose of caffeine along with fats that can be used for energy, bulletproof coffee can help maintain energy levels even when fasting. This is preferable for some people compared to the energy crashes that can occur when fasting without bulletproof coffee. The fats and caffeine provide fuel to power through the morning.

Appetite Suppression and Potential Weight Loss

Many people find that the satiating effect of bulletproof coffee’s healthy fats helps suppress appetite during the fasting period. This makes it easier to stick to the fast without excessive hunger. By reducing overall calorie intake, intermittent fasting paired with bulletproof coffee may spur weight loss over time for some people. However, individual results can vary.

Potential Drawbacks

Drinking bulletproof coffee while fasting does come with some potential drawbacks to consider:

High Calorie Content

One of the main concerns with bulletproof coffee is that it can be very high in calories. A typical recipe calls for at least 1-2 tablespoons of grass-fed butter or ghee and 1-2 tablespoons of MCT oil. Just one tablespoon of butter or oil contains 100 calories or more. This means a single cup of bulletproof coffee can easily provide 200-400 calories, essentially breaking your fast.

While the fats in bulletproof coffee may provide satiety and energy, consuming so many liquid calories could counteract some of the potential benefits of fasting. It may be better to limit bulletproof coffee intake or modify the recipe to reduce the calorie load.

High Fat Content

In addition to being calorie-dense, bulletproof coffee is also extremely high in fat, again thanks to the generous amounts of butter or ghee and MCT or coconut oil. Consuming upwards of 30-40 grams of fat in one drink could lead to unwanted side effects.

Too much dietary fat, especially saturated fat, may raise cholesterol levels or cause gastrointestinal issues in some individuals. Those with gallbladder problems may also want to avoid high fat meals like bulletproof coffee.

Moderating your fat intake from bulletproof coffee by adjusting the recipe or frequency could help avoid potential downsides.

Individual Variations

Finally, people can react differently to consuming bulletproof coffee during a fast. Some may tolerate it with no problem, while others may find it disrupts their fast or ketosis. There are many individual factors like metabolism, gut health, and diet preferences that can impact responses.

Paying attention to how your body reacts to bulletproof coffee and being prepared to modify or eliminate it from your fasting protocol is wise. What works for someone else may not work for you when it comes to mixing coffee and fasting. Proceed cautiously and adjust as needed.

Nutritionist Recommendations

Nutrition experts have varying perspectives when it comes to consuming Bulletproof Coffee during a fast. Here are some of their key recommendations and concerns:

Suggested Protocols

  • Limit Bulletproof Coffee to 1-2 cups per day maximum during fasting periods. Consuming too much can blunt ketosis and fat burning.
  • Have Bulletproof Coffee in the morning or early afternoon. Late day consumption can disrupt circadian rhythms and sleep quality.
  • If doing alternate day fasting, restrict Bulletproof Coffee to 500 calories or less on fast days. This preserves many of the benefits.
  • For fat fasts, Bulletproof Coffee is acceptable but limit other high fat foods and total calories to promote ketosis.

Potential Benefits

  • The fats in Bulletproof Coffee can increase satiety and suppress appetite during the fasting window. This makes fasting more sustainable long-term.
  • Bulletproof Coffee provides energy and mental clarity to remain productive during periods of calorie restriction.
  • Adding MCT oil to Bulletproof Coffee may enhance ketone levels and boost fat burning.

Potential Concerns

  • – Overdoing Bulletproof Coffee intake can slow fat burning during fasts. Nutritionists recommend moderation.
  • – Some individuals may be sensitive to dairy or coffee and experience adverse effects from Bulletproof Coffee.
  • – Relying too heavily on Bulletproof Coffee can prevent adapting metabolically to burning stored body fat.

How to Make Bulletproof Coffee

Bulletproof Coffee is simple to make at home with just a few key ingredients. Here is a step-by-step guide:


– 1-2 cups of hot brewed coffee
– 1-2 tablespoons of grass-fed, unsalted butter
– 1-2 tablespoons of MCT oil or coconut oil
– Optional: collagen peptides or protein powder


  1. Brew 1-2 cups of coffee using your preferred method (french press, pour over, etc). Allow it to cool slightly so it’s hot but not scalding.
  2. Add the butter and MCT/coconut oil to a blender. You can also use a milk frother instead of a blender if you prefer a frothier coffee.
  3. Pour the hot coffee into the blender. Make sure to leave room at the top so it doesn’t overflow when blending.
  4. Blend for 20-30 seconds until the coffee turns a creamy, frothy texture.
  5. Pour into your favorite mug and enjoy! Be careful as the coffee will still be hot after blending.


  • Use grass-fed butter for maximum nutrition benefits. Kerrygold is a popular brand.
  • Coconut oil or MCT oil help make the coffee creamy. MCT oil also provides an extra energy boost.
  • Adding collagen peptides or protein powder boosts protein. But some may consider this breaking your fast.
  • Store leftovers in the fridge and reheat or blend again before drinking.
  • Customize flavors with a dash of cinnamon, vanilla, cocoa powder, or your favorite low carb sweetener.
  • Adjust amounts of butter and oil to reach your desired richness and consistency.

Frequently Asked Questions

Does the amount of bulletproof coffee consumed affect whether it breaks your fast?

The amount of bulletproof coffee you drink can impact your fasted state. Consuming small amounts like 1-2 tbsp of butter or MCT oil in your coffee is less likely to influence ketosis or insulin levels. However, drinking very large servings with excessive calories and fat could potentially break your fast. Moderation is key.

What about using alternative fats like coconut oil instead of butter?

Substituting the typical grass-fed butter in bulletproof coffee with other fats like coconut oil, avocado oil, or ghee does not inherently break your fast. The type of fat matters less than the total calorie and macronutrient profile. That said, MCT oil and butter may provide more benefits for energy, cognition, and appetite control.

Can I add protein powder or collagen to my bulletproof coffee while fasting?

Adding protein powders, collagen peptides, or other protein sources to your bulletproof coffee is generally not recommended when fasting. Consuming protein spikes insulin and could inhibit the benefits of fasting. Keep bulletproof coffee simple – stick to coffee, butter/MCT oil, and optional spices only.

Is it better to drink bulletproof coffee in the morning or afternoon when fasting?

Most people prefer consuming bulletproof coffee in the morning or early afternoon during the fasting window. This provides an energy boost and suppresses hunger early on. Drinking it too late could impair sleep. Find the timing that works best for your schedule and hunger patterns.

For more bulletproof coffee FAQs, check out these additional resources:

  • Bulletproof’s Official FAQ on Fasting –
  • Perfect Keto’s Guide to Bulletproof Coffee for Fasting –
  • Diet Doctor’s Bulletproof Coffee Article –

Key Takeaways


Based on the information provided, the debate around whether bulletproof coffee breaks a fast remains inconclusive. Proponents argue it provides energy and suppresses hunger without an insulin spike, while critics say the calories and fat can inhibit ketosis. Ultimately, it seems to depend on the individual and their specific goals. Many can tolerate small amounts without adverse effects.

Final thoughts

In moderation, bulletproof coffee may provide a helpful boost during intermittent fasting for some people. It likely does not technically “break” the fasted state for most. However, more research is still needed on its long-term impacts. Individuals should experiment mindfully and adjust intake based on how they feel and their progress.


For those looking to incorporate bulletproof coffee into an intermittent fasting protocol, here are some tips:

  • Start with 1-2 cups per day maximum
  • Use grass-fed butter and MCT or coconut oil
  • Blend well to emulsify the fats
  • Avoid adding sugars, flavors or excessive calories
  • Listen to your body and adjust as needed
  • Stay well hydrated with plain water
  • Consider having coffee later in the fasted period
  • Monitor weight, appetite and energy levels
  • Consult a healthcare provider if concerned

With mindful consumption, bulletproof coffee may be an intermittent faster’s friend. But as with any dietary change, moderation and customization to individual needs is key.

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