Can I drink coffee while fasting is one of the most common questions people ask when they start intermittent fasting. Good news for coffee lovers. You can drink black coffee during your fast and it will not break it. A standard cup of black coffee has about 3 to 5 calories, almost zero fat, zero protein and zero sugar. Your body will stay in a fasted state.
Research published in Clinical Nutrition ESPEN in 2021 tested 15 healthy adults who drank 240ml of black instant coffee or water before a high fat meal. The study found no difference in fasting triglyceride or glucose levels between the two groups. Black coffee does not spike your insulin or start digestion.
Does black coffee break a fast?
No. Black coffee does not break a fast. A cup of black coffee contains fewer than 5 calories and has no carbs or protein that would trigger an insulin response. Many intermittent fasting research protocols actually allow black coffee during the fasting window because it does not interfere with the metabolic benefits.
A 2020 study from Oklahoma State University confirmed this. Researchers gave participants either water or black coffee after a 10 hour overnight fast, then measured their metabolic response. There was no difference between the two groups. Your body stays in fat burning mode when you drink plain black coffee.
Will coffee help me fast longer?
Yes. Coffee makes fasting easier because it suppresses appetite and reduces hunger. A review published in the International Journal of Food Sciences and Nutrition found that caffeine consumed 30 minutes to 4 hours before a meal can reduce how much you eat at that meal.
Another study gave overweight and obese participants coffee with 6mg of caffeine per kg of body weight at breakfast. They ate 550 fewer calories during the rest of the day compared to people who just drank water. The caffeine and other compounds in coffee signal to your brain that you are not hungry.
Decaffeinated coffee also works. A randomised controlled trial with 11 healthy men tested caffeinated coffee, decaffeinated coffee and plain water. Decaffeinated coffee reduced hunger for the entire 180 minute study period and increased levels of peptide YY, a hormone that makes you feel full. This tells us caffeine is not the only ingredient in coffee that controls appetite. The chlorogenic acids and polyphenols help too.
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Does coffee increase fat burning during a fast?
Yes. Drinking black coffee boosts your metabolic rate and helps your body burn fat for fuel. A 2017 study found that caffeine can increase fat oxidation by up to 29% when taken before exercise.
Coffee also helps produce ketones. When you fast, your body switches from burning glucose to burning fat and produces ketones for energy. A study gave 10 healthy adults caffeine at doses of 2.5 and 5.0 mg per kg. Both doses increased ketone production in a dose dependent way. More caffeine meant more ketones.
This makes coffee and fasting a powerful combination. You get the fat burning benefits of fasting plus the metabolic boost from coffee.
Does coffee boost autophagy?
Yes, it appears so. Autophagy is your body’s natural clean up process where it breaks down and recycles damaged cells. This is one of the main reasons people fast for longevity and health.
A 2014 study published in Cell Cycle found that both regular and decaffeinated coffee triggered autophagy in mice within 1 to 4 hours. Researchers saw increased autophagy in the liver, muscle and heart tissue. The polyphenols in coffee, not just the caffeine, seem to activate this cellular clean up process.
This means black coffee might actually enhance the autophagy benefits of fasting rather than block them. Coffee can mimic some effects of caloric restriction and help your body enter a deeper fasted state.
What can I add to coffee without breaking my fast?
Black coffee is the safest choice. But if you need a bit of flavour, here are your options.
- Cinnamon or nutmeg in small amounts, less than half a teaspoon, adds flavour without calories
- A tiny splash of unsweetened almond milk, around 15ml or a tablespoon, adds only about 2 calories
- Stevia or other non nutritive sweeteners do not spike insulin and contain zero calories
Anything with calories from fat, protein or carbs can slow or stop the fasting benefits. Sugar, milk, cream, honey, flavoured syrups and regular creamers will break your fast.
What breaks a fast?
Any food or drink with calories from carbohydrates, proteins or fats will break a fast. When you consume these macronutrients, your body starts digestion, releases insulin and shifts out of the fasted state.
Here is what will break your fast.
- Milk and cream, even a small amount contains protein, fat and carbs
- Sugar, honey, maple syrup and flavoured syrups
- Bulletproof coffee with butter and MCT oil, this contains about 230 to 450 calories
- Protein powder or collagen
- Any food, even healthy foods
If your goal is weight loss, some people argue that a small amount of fat from butter or MCT oil will keep you in ketosis while technically breaking the fast. But if your goal is autophagy and cellular clean up, you want to keep calories as close to zero as possible during your fast.
How much coffee can I drink while fasting?
Up to 3 to 4 cups of black coffee per day is safe for most people. Research consistently links this amount with health benefits including reduced risk of type 2 diabetes, heart disease and certain cancers.
More than 400mg of caffeine per day, about 4 cups, can cause side effects like anxiety, trouble sleeping, increased heart rate and jitteriness. People who are sensitive to caffeine may need to drink less.
The timing matters too. Drink coffee in the morning or early in your fasting window. Avoid drinking it late in the day or it may interfere with your sleep. Poor sleep can mess with your hunger hormones and make fasting harder the next day.
Does decaf coffee break a fast?
No. Decaffeinated coffee does not break a fast. It has the same near zero calorie content as regular coffee and will not trigger an insulin response.
The 2014 Cell Cycle study found that decaffeinated coffee triggered autophagy just as well as regular coffee. Both types contain polyphenols and chlorogenic acids that provide health benefits beyond caffeine.
Decaf is a good option if you are sensitive to caffeine or want to drink coffee later in the day without affecting your sleep.
Does coffee affect blood tests while fasting?
Yes, coffee can affect some blood test results. A 2020 study in the British Journal of Nutrition found that caffeine can alter lipid levels, C reactive protein and some hormone related biomarkers, especially in older adults.
For routine blood work, including fasting glucose and cholesterol tests, most doctors recommend drinking only water. The caffeine in coffee raises cortisol and releases fatty acids into your bloodstream. This can throw off your results.
If you have a blood test coming up, ask your doctor whether coffee is allowed. When in doubt, stick to water for the most accurate results.
FAQ
Can I drink coffee with milk while fasting?
No. Milk contains protein, fat and carbs that will trigger digestion and break your fast. Even a splash of milk adds calories and can reduce fasting benefits.
Will black coffee kick me out of ketosis?
No. Black coffee has no carbs and will not affect ketosis. It may actually boost ketone production.
Can I drink coffee before a fasted workout?
Yes. Drinking black coffee 30 to 45 minutes before exercise can increase fat burning and improve performance. A study found caffeine boosts exercise performance by 11 to 12 percent.
Does coffee cause dehydration during fasting?
No. A 2014 study from the University of Birmingham found that 4 cups of coffee provided the same hydration as 4 cups of water in regular coffee drinkers.
How many calories break a fast?
There is no official number, but most experts suggest staying under 10 calories to maintain autophagy benefits. Black coffee at 3 to 5 calories per cup keeps you well under this.
Can I drink iced coffee while fasting?
Yes, as long as it is black with no added sugar, milk or flavourings. Plain cold brew and iced black coffee are fine.
Is espresso okay during a fast?
Yes. A single shot of espresso has about 3 calories and will not break your fast.
Can I use artificial sweeteners in my coffee while fasting?
Most non nutritive sweeteners like stevia, erythritol and monk fruit do not spike insulin and contain zero calories. They should not break your fast for weight loss purposes. Some research suggests they may slightly interfere with autophagy, but the evidence is mixed.
Coffee during a fast is one of the most common questions in intermittent fasting, and the answer largely depends on what you add to it. Mental health also plays a role in sustaining any dietary protocol, so understanding concepts like splitting in BPD can help you recognise emotional eating triggers. If you’re combining fasting with high-protein meals, you may also want to know whether eating 6 eggs a day is safe. A personal trainer in Yarraville can help you integrate fasting with a training plan that suits your lifestyle.
