Drinking moderate amounts of very low- or zero-calorie beverages during a fasting window is unlikely to compromise your fast in any significant way.

This includes drinks like black coffee.

One cup (240 ml) of black coffee contains about 3 calories and very small amounts of protein, fat, and trace minerals (2).

For most people, the nutrients in 1–2 cups (240–470 ml) of black coffee aren’t enough to initiate a significant metabolic change that would break a fast (3, 4).

Some people say that coffee suppresses your appetite, making it easier to stick with your fast in the long term. However, this claim remains scientifically unproven (5).

Overall, drinking coffee moderately won’t significantly disrupt your intermittent fast. Just be sure to keep it black, without any added ingredients.

Summary Black coffee is unlikely to hinder the benefits of intermittent fasting. It’s generally fine to drink it during fasting windows.

Surprisingly, coffee may enhance many of the benefits of fasting.

These include improved brain function, as well as reduced inflammation, blood sugar, and heart disease risk (1).

Metabolic benefits

Chronic inflammation is a root cause of many illnesses. Research suggests that both intermittent fasting and coffee intake may help reduce inflammation (1, 6).

Some research suggests that higher coffee intake is associated with a decreased risk of metabolic syndrome, which is an inflammatory condition characterized by high blood pressure, excess body fat, high cholesterol, and elevated blood sugar levels (7, 8).

Studies also link coffee intake to a decreased risk of type 2 diabetes. What’s more, up to 3 cups (710 ml) of coffee per day is associated with a 19% reduced risk of death from heart disease (9, 10, 11).

Brain health

One of the major reasons intermittent fasting has surged in popularity is its potential to promote brain health and protect against age-related neurological diseases.

Interestingly, coffee shares and complements many of these benefits.

Like intermittent fasting, regular coffee consumption is associated with a reduced risk of mental decline, as well as Alzheimer’s and Parkinson’s diseases (12).

In a fasted state, your body produces energy from fat in the form of ketones, a process linked to improved brain function. Early research indicates that the caffeine in coffee may likewise promote ketone production (13, 14).

Intermittent fasting may also support brain health through increased autophagy (14).

Autophagy is your body’s way of replacing damaged cells with healthy ones. Research suggests that it may safeguard against age-related mental decline (16).

Furthermore, a study in mice tied coffee to significantly increased autophagy (17).

Thus, it may be especially beneficial to include moderate amounts of coffee in your intermittent fasting regimen.

Summary Coffee shares many of the same benefits as fasting, including reduced inflammation and improved brain health.

Although coffee alone isn’t likely to break your fast, added ingredients could.

Loading up your cup with high-calorie additives like milk and sugar can disrupt intermittent fasting, limiting the benefits of this dietary pattern.

Many popular health and media outlets claim that you won’t break your fast as long as you stay under 50–75 calories during each fasting window. However, no scientific evidence backs these claims.

Instead, you should consume as few calories as possible while fasting.

For instance, lattés, cappuccinos, and other high-calorie or sweetened coffee drinks should be off-limits during your fasting windows.

While black coffee is the best choice, if you have to add something, 1 teaspoon (5 ml) of heavy cream or coconut oil would be good options, as they’re unlikely to significantly alter your blood sugar levels or total calorie intake.

Other considerations

A single cup (240 ml) of coffee contains about 100 mg of caffeine (2).

Consuming too much caffeine from coffee could lead to side effects, including heart palpitations and temporary increases in blood pressure (18).

One study found that high coffee intake — up to 13 cups (3.1 liters) per day — resulted in increased fasting insulin levels, suggesting a short-term decrease in insulin sensitivity (3).

If you’re using intermittent fasting to improve your fasting insulin levels or increase your insulin sensitivity, you’ll want to moderate your coffee intake.

Moreover, excessive caffeine intake could harm your sleep quality. Poor sleep can harm your metabolic health over time, which could negate the benefits of intermittent fasting (19, 20).

Most research indicates that up to 400 mg of caffeine per day is likely safe for most people. This equates to about 3–4 cups (710–945 ml) of regular coffee per day (18).

Summary If you drink coffee during your fasting periods, avoid high-calorie, high-sugar additives, as they may break your fast.

Ultimately, drinking coffee during a fast is up to personal preference.

If you don’t like coffee or don’t currently drink it, there’s no reason to start. You can obtain many of the same health benefits from a diet rich in whole, nutritious foods.

However, if a hot cup of joe seems to make your fast a little easier, there’s no reason to quit. Just remember to practice moderation and avoid extra ingredients.

If you find that you’re overconsuming coffee or having trouble sleeping, you may want to cut back and focus solely on intermittent fasting.

Summary Drinking a moderate amount of black coffee during intermittent fasting is perfectly healthy. Still, you’ll want to moderate your intake and avoid most additives like sugar or milk.

You can drink moderate amounts of black coffee during fasting periods, as it contains very few calories and is unlikely to break your fast.

In fact, coffee may enhance the benefits of intermittent fasting, which include reduced inflammation and improved brain function.

Nonetheless, you should steer clear of high-calorie additives.

It’s also best to watch your intake, as overconsumption can harm your health.