The Top Do's & Don'ts Of Drinking Coffee While Fasting

If you intermittent fast but like your morning cup of joe, you may be asking if you can drink coffee during your non-eating periods without technically "breaking" your fast. You're probably also wondering if drinking coffee on an empty stomach delivers any health advantages—or totally derails the benefits of fasting.

We consulted with health and nutrition experts on this comprehensive guide to drinking coffee while fasting: the pros, the cons, and how to do it most effectively for metabolic health and longevity benefits.

Intermittent fasting (IF) involves cycling between periods of fasting and periods of nutrient consumption.

Time-restricted eating (TRE) is a type of intermittent fasting that involves limiting food intake to a short hourly window each day and fasting for the remaining time. Example ratios include 16:8 and 18:6, with the first number being the hours you spend not eating during a 24-hour period.

"Food or absence of food can help regulate our internal clocks1, turning our genes off and on and regulating metabolism," adds Jaime Seeman, M.D., board-certified OB-GYN, and the host of the Fit and Fabulous podcast. "Independent of weight loss, people who use time-restricted eating have improved insulin2 and glucose levels3 as well as improvements in blood pressure2." 

Fasting also has benefits that go beyond metabolic health to potentially aid longevity4. "Eating in a narrower window each day, particularly if most of the calories are taken in the morning and early afternoon, has been shown to increase the amount of time the body spends making vital repairs that can save us from diseases5 we don't yet have and might halt or even reverse some diseases we do have," says journalist Steve Hendricks, author of The Oldest Cure in the World: Adventures in the Art and Science of Fasting. 

You can think of the fasting period as a time for your body to go into "cellular housekeeping6" mode. "Among the repairs the body accelerates during time-restricted eating," Hendricks adds, "are patching up damaged or miscopied DNA, producing more antioxidants to fight off the daily assault from free radicals, and increasing autophagy7, which is the recycling of worn-out cellular parts."

Now for the questions you're here for: Does coffee break a fast? And can you have your java without disrupting the benefits of time-restricted eating?

The answers aren't so clear-cut. A cup of black coffee contains very few calories, only about two, so the caloric impact on the fast is likely minimal. The caffeine in coffee, however, will technically affect your fast, though it's not entirely clear how much it gets in the way of fasting benefits.

"Caffeinated drinks, even noncaloric ones," Hendricks explains, "almost certainly disturb a fast, but scientists don't yet know precisely in what ways or to what extent. What we know with certainty is that even a modest amount of caffeine, particularly in the morning, resets our circadian clocks8. But to what extent morning caffeine also fires up our metabolism and pulls us out of our body's fasting-and-repair mode is, so far as I know, still uncertain."

One thing we do know, notes Pedre, is that many popular coffee additives will further break your fast. "What breaks any fast," he says, "is when you cause an insulin spike, which would be caused by eating carbohydrates or taking sugar in your coffee, for example." The caveat is that coffee can trigger insulin release9 even without sugar or carbohydrates, he adds.

"Anything that contains a calorie can impact fasting," Seeman echoes. "This goes for carbs, fats, proteins, and alcohol. These nutrients activate our internal clocks and essentially 'break' our time-restricted eating window."

This means that ultimately, the decision about whether to drink coffee (and how to take it) while fasting is largely a personal one. It depends on how much of a purist you are about fasting and how much you value that morning cup of coffee. It's worth noting that coffee consumption in general may also have some metabolic health benefits (noted below), so those are also worth considering when weighing your decision to caffeinate or not. 

If you do head for the coffeepot or hit up your favorite barista during your fast, you may want to limit yourself to one serving. "As for whether the quantity of coffee matters," Hendricks says, "we, unfortunately, don't have good data to say. But one would expect that the more caffeine, the more disruption to the fast."

This is always good advice to follow, whether or not you're fasting. "Drinking caffeine after noon or 2 p.m. for most individuals will interrupt the quality of their sleep, even if that is occurring many hours later," says Pedre. This is due to the relatively long half-life of caffeine.

Experts also recommend sticking to black coffee while fasting if you can. If plain joe doesn't do it for you, though, some additives will disrupt a fast's benefits less than others.

Here's the scoop on several common coffee adds and how they impact a fast:

One teaspoon of cinnamon has about 6 calories. A light sprinkle of cinnamon in your black coffee won't impact your fast much more than the coffee itself, making it a good flavoring option for those who are strict about fasting. Plus, cinnamon has beneficial effects for blood sugar10 for people with prediabetes or Type 2 diabetes.

Just one level teaspoon of granulated sugar (4 grams) has about 16 calories. Sugar will break your fast. Additionally, added sugar consumption drives insulin resistance11 and is a contributor to metabolic diseases such as Type 2 diabetes12 and cardiovascular disease13.

One ounce of whole milk contains about 17 calories and about 1.3 grams of carbohydrates in the form of lactose, a type of sugar. So milk will also break your fast. Also, dairy can produce a high insulin response14. More research is needed to determine whether dairy consumption has implications for insulin resistance.

Depending on the type, 1 tablespoon of cream contains anywhere from about 10 to 50 calories. Cream will break your fast. Many flavored coffee creamers also contain added sugar that drives up calories and can be detrimental to your metabolic health.

With more than 100 calories per tablespoon, medium-chain triglycerides, or MCTs, will technically break your fast. But MCT oil is 100% fat, with no carbohydrates or protein, meaning that it's ketogenic-diet-friendly. A keto diet encourages the production of ketone bodies, which may also encourage autophagy15.

MCT oil may have some metabolic health benefits, including supporting weight management16. The fat consumption may provide energy, help you feel fuller, and prevent a subsequent blood glucose (sugar) drop brought on by the caffeine-driven insulin release. 

"Some people do quite well with coffee, butter, and MCT oil without tanking their blood glucose," explains Pedre, "and these individuals may be able to have coffee early in the morning while still fasting and maintain the fasted state until lunchtime in the afternoon." 

Seeman adds that someone may consume MCT oil during a fasting window as a way to boost ketone levels and enhance cognition17. "In this case," she says, "it all depends on what someone's goals are."

Coconut oil is a main source of MCTs, but MCT oil will be 100% MCTs, whereas coconut oil will only contain about 65% MCTs18. For this reason, if you're considering adding an oil to your coffee during fasting, you may wish to choose an MCT oil. MCT oil may also have more benefits when it comes to feeling fuller19 when compared to coconut oil, according to research in Physiology & Behavior. However, both options are keto-friendly.

One tablespoon of olive oil contains over 100 calories and will break your fast. But as with MCT oil, olive oil's calories come from fats, so it's keto-friendly and also has metabolic health benefits.

One ounce of plain, unsweetened almond milk has about 5 calories. So again, technically it will break your fast. But if you just need a little something to jazz up your java, likely a tiny splash won't impact it too much beyond what's already occurring with the coffee. Just make sure it's unsweetened.

One tablespoon of butter or ghee, a type of clarified butter, has over 100 calories. So butter will technically break your fast. But as an all-fat food source, butter will not spike blood sugar. As Pedre notes, many people who are intermittent fasting or following a keto diet will add MCT oil and butter or ghee to their coffee to help tide them over until their next meal.

Combining coffee consumption with intermittent fasting may have health benefits of its own. "In studies on time-restricted eating," Seeman points out, "most participants are allowed to drink plain coffee or tea. In people who consume these during fasting, there is improvement in glucose regulation and slight increase in weight loss, likely due to caffeine and polyphenols."

Here's the science behind why this can be a beneficial pairing:

Research has found that drinking coffee in moderation can reduce one's risk of Type 2 diabetes20 and metabolic syndrome21, a condition that's present when someone has three or more of the following: high blood sugar, blood pressure, cholesterol, triglycerides, or waist circumference. 

Low-grade inflammation is a hallmark of many chronic conditions, including Type 2 diabetes and metabolic syndrome. Coffee consumption specifically (not just caffeine) is associated with a reduction in pro-inflammatory markers22.

"The benefits of coffee are mostly related to the polyphenols it contains," Seeman says. Polyphenols23 are plant compounds that act as antioxidants.

"Polyphenols help with glucose regulation in the liver," Seeman says. This could explain some of the associations we see with coffee consumption and reduced risk of Type 2 diabetes and metabolic syndrome. But there's likely more to the link. "Coffee boosts both thermogenesis24 immediately and metabolic rate25, meaning using fats as fuel, for up to 24 hours," Pedre adds.

Like coffee, intermittent fasting also helps control inflammation by boosting a protein called galectin-326, according to preliminary research. Fasting also drives thermogenesis, promoting the browning of white adipose tissue27, important for weight management and insulin sensitivity.

Finally, "[Polyphenols] also stimulate autophagy within the liver," Seeman adds, "clearing out dead and damaged cells." And intermittent fasting boosts autophagy7, as well.

"Correlation studies show a reduced risk of many diseases like stroke28, Alzheimer's28, and Parkinson's29 disease amongst coffee drinkers," Seeman says. Again, the polyphenols are likely at work here, but another reason may be that autophagy helps protect against age-related neurogenerative decline30.

The short-term benefits of coffee on the body and brain include increased mental focus and alertness31 and increased exercise performance32. The caffeine is at work here, and it may provide a welcome jolt if you're feeling low energy from fasting.

"If you ingest caffeine on an empty stomach, it will have a more potent stimulant effect that will also tend to increase the level of jitteriness that caffeine can produce," Stanford neuroscientist Andrew Huberman, Ph.D., notes on the Huberman Lab Podcast.

And some coffee drinkers are going to feel this more than others. "Some people are going to be very sensitive to coffee triggering an insulin response, even if the coffee is black or only has fat but no sugar," Pedre says. "When the pancreas releases insulin, blood sugar will drop subsequently. And within 30 to 60 minutes of drinking coffee, a blood sugar drop will cause uncomfortable weakness, shaking, and cravings for carbs or sugar."

These regular crashes could have long-term impacts. "It may even lead to the overconsumption of calories over the rest of the day," Pedre says, "which will cause weight gain in most individuals." 

If you experience these "crash" symptoms, you may wish to wait until you break your fast to drink your coffee. Alternatively, you could wait until just 30 minutes before you break your fast, Pedre adds. That way you can use food to mitigate any blood sugar plummet. Another potential way to limit a crash is to add MCT oil and ghee to your cuppa. Huberman also says adding 100 mg of L-theanine can offset some of the jitteriness.

Another potential side effect of drinking coffee on an empty stomach is gastrointestinal upset. "Coffee on an empty stomach can trigger the release of hydrochloric acid33," Pedre explains, "leading to an acid stomach, heartburn, and acid reflux." Excessive coffee consumption in a fasted state, over time, can also lead to abdominal pain and nausea, he adds.

If you have a history of gallbladder attacks, you may wish to avoid coffee, especially on an empty stomach. "Coffee induces the release of a hormone called cholecystokinin34 [CCK]," Seeman adds, "which causes gallbladder contractions. People with underlying gallstones can get symptomatic with ingestion of coffee."

Finally, be aware of how much coffee you consume and if you have any restrictions on caffeine intake regarding underlying conditions. "Excessive caffeine intake has risks35, including poor sleep, high blood pressure, headaches, anxiety, and more," Seeman notes. "The recommended upper limit of caffeine is no more than 400 milligrams per day for adults."

Hendricks notes that drinking only water is the least disruptive way to stay hydrated during a fasting period. If you want to add other beverages to the mix, he recommends options that are noncaloric, noncaffeinated, and don't contain ingredients and additives that will tax your digestive tract. Here are some fasting-friendly options:

If we're being strict about it, coffee does technically break a fast. However, a cup of coffee's effects will likely be minimal if you drink it black (and it could even complement certain IF benefits). Some people may be sensitive to a blood sugar drop after coffee consumption on an empty stomach. If that's you and you're set on your java, keep things keto by adding MCT oil and ghee. You'll still reap some metabolic health benefits, despite breaking your fast.