Does Instant Coffee Break a Fast? Dr. Berg's Take on Your Morning Brew

October 15, 2025 •

4 min read

With the increasing popularity of intermittent fasting, many coffee lovers wonder how their daily routine fits in. While it's a common question, Dr. Berg's guidance is clear: plain black instant coffee will not break a fast, provided it contains no additives that trigger an insulin response.

Quick Summary

According to Dr. Berg, plain black instant coffee is permissible during fasting. However, adding sugar, milk, flavored creamers, or certain sweeteners will disrupt your fasted state, impacting fat burning and autophagy. The key is to avoid any ingredient that spikes insulin.

Key Points

Dr. Berg's Take: Plain black instant coffee does not break a fast, as it contains negligible calories and does not trigger an insulin spike.
Insulin Control is Key: Dr. Berg's fasting rules focus on keeping insulin levels low. Any food or drink that raises insulin, regardless of calorie count, ends the fast.
Additives are the Problem: The most common additions like sugar, milk, and cream are what break a fast. You must avoid these to maintain the fasted state.
Bulletproof Coffee Nuance: While popular on keto, bulletproof coffee made with fats like MCT oil and butter technically breaks a true fast due to its caloric content, though it keeps insulin low.
Consider Your Goals: For maximum cellular cleanup (autophagy), stick to pure black coffee or water. For weight loss, a strict approach is best, but some practice 'dirty fasting' with minimal additives.
Artificial Sweeteners: Many artificial sweeteners are advised against, as they can still impact metabolism and trigger cravings, according to Dr. Berg.

Dr. Berg's Core Fasting Principles

Dr. Eric Berg, a prominent figure in the keto and fasting community, bases his nutritional advice on managing insulin levels. His core philosophy revolves around the idea that for fasting to be effective—especially for weight loss and metabolic health—you must avoid consuming anything that raises insulin. A food or drink’s effect on insulin, not just its calorie count, is the determining factor in whether it breaks a fast. This applies equally to both regular and instant coffee.

The Green Light for Black Instant Coffee

For those who depend on their daily cup of joe, the good news is that plain instant coffee is generally safe for fasting, according to Dr. Berg. Here's why:

Minimal Calories: A cup of plain black coffee, including instant coffee, contains a negligible amount of calories (typically fewer than 5 per cup). This tiny amount is unlikely to trigger a significant metabolic change.
No Insulin Spike: Plain coffee has no carbohydrates or sugar, so it doesn't cause an insulin response. This allows your body to remain in a fasted, fat-burning state.
Potential Fasting Benefits: Coffee itself may even enhance some fasting benefits. The caffeine can help suppress appetite, increase mental alertness, and boost fat-burning by stimulating the nervous system.

The Red Flags: Additives That Will Break a Fast

While instant coffee itself is fine, what you add to it is critical. Dr. Berg and other fasting experts advise against most popular coffee additions.

Sugar: Any form of sugar or sugary syrup will immediately break your fast. Sugar provides a rapid source of glucose, causing an insulin spike that halts the fat-burning process.
Milk and Creamers: Dairy products contain lactose (milk sugar) and protein, which can trigger an insulin response. This includes cow's milk, oat milk, and even most almond milk products that contain added sugars or emulsifiers.
Artificial Sweeteners: Many non-caloric artificial sweeteners like aspartame or sucralose can still affect insulin levels or the gut microbiome, and may perpetuate cravings for sweet things. Dr. Berg recommends avoiding these for a strict fast. However, natural sweeteners like stevia or monk fruit may be acceptable in minimal amounts for those focused on weight loss, though they should be avoided for strict autophagy.

Instant vs. Brewed Coffee: Is There a Difference?

From a fasting perspective, there is no significant difference between plain instant coffee and plain brewed coffee. The freeze-drying process that creates instant coffee granules does not add enough calories or carbs to affect a fast. The key is the absence of additives. A study in the American Journal of Clinical Nutrition found that plain instant coffee consumption had no effect on insulin sensitivity or fasting glucose levels.

Fasting Goals: How Context Changes the Rules

Your specific fasting goals can also influence the rules. The approach for weight loss may differ slightly from the approach for maximizing cellular repair (autophagy).

For Weight Loss and Metabolic Health: For most people, a strictly black instant coffee is the best choice. Some who practice a less strict approach, sometimes called "dirty fasting," may allow a very small amount of heavy cream or healthy fat like MCT oil. However, this is not a true fast, as it introduces calories.
For Autophagy: If your primary goal is to maximize autophagy—the cellular clean-up process—then it's best to stick to zero-calorie beverages exclusively. Even minimal calories or compounds that activate the mTOR pathway could potentially slow or inhibit this process. For this purpose, pure black coffee or water are the safest options.

How Common Coffee Additions Affect Your Fast

To clarify what's acceptable, consider this table based on Dr. Berg's principles:


Addition	Fasting Status (Dr. Berg's View)	Reason
Black Instant Coffee	Safe	Contains negligible calories and no carbs; won't spike insulin.
Sugar	Breaks Fast	Rapidly raises blood sugar and insulin levels.
Milk/Creamer	Breaks Fast	Contains lactose (sugar) and protein, triggering an insulin response.
Stevia/Monk Fruit	Generally Safe (Weight Loss)	Does not cause an insulin spike but might affect gut health or cravings; avoid for strict autophagy.
MCT Oil/Butter	Technically Breaks Fast	High-fat but caloric; stops a pure fast but supports ketosis.
Artificial Sweeteners	Breaks Fast (Strict)	Can still trigger metabolic responses and cravings.

Conclusion: Keeping it Black is the Safest Bet

So, does instant coffee break a fast Dr. Berg endorses? The verdict is clear: not if you consume it plain and black. Any caloric additions, especially sugar and dairy, will end your fast by causing an insulin spike. For the best results, stick to black coffee and water. Consider your specific fasting goals, whether for fat loss or maximum autophagy, and adjust your coffee consumption accordingly. When in doubt, prioritize simplicity to maintain your fasted state and reap the full benefits of your fasting regimen. For more on what is and isn't allowed during a fast, you can consult Dr. Berg's official resources.

Frequently Asked Questions

Dr. Berg suggests caution with all sweeteners during a fast. While natural, zero-calorie options like stevia or monk fruit may be acceptable for some weight loss goals due to minimal insulin impact, they should be avoided for strict fasting aimed at maximizing autophagy or achieving gut rest.

Instant coffee without additives has virtually zero calories and no carbohydrates, preventing an insulin spike. In contrast, milk contains lactose (sugar) and protein, and added sugar is a direct carbohydrate source, both of which raise insulin and break the fasted state.

No, black instant coffee does not negatively affect ketosis. In fact, caffeine can help mobilize fatty acids for energy, which supports the body's fat-burning state.

From a fasting standpoint, there is no significant difference between black instant and black brewed coffee. Both have a minimal caloric and nutritional profile that won't disrupt the fasted state.

'Dirty fasting' is a less strict form of intermittent fasting where minimal calorie intake, often from small amounts of healthy fats like heavy cream or MCT oil in coffee, is allowed. This technically breaks a pure fast but is intended to help curb hunger while staying in a fat-burning state. Dr. Berg recommends sticking to pure black coffee for best results.

Moderation is key. While plain black instant coffee won't break your fast, consuming too much caffeine (generally over 400mg, or about 4 cups) can increase cortisol levels and potentially interfere with sleep. It's recommended to stick to 1-2 cups per day during your fasting window.

Most flavored instant coffees contain sugars, syrups, or artificial sweeteners that will break a fast. Unless the flavor comes from a zero-calorie, zero-insulin-impact source, it should be avoided during the fasting window.