Can you drink coffee while fasting?
Updated
Two registered fasting studies allowed black coffee during fasting hours, and the CDC calls plain coffee a low-calorie choice. What changes the answer is what goes in the cup and what kind of fast you're doing. For a fast before a blood test, skip the coffee.
None of the sources used here defines exactly what "breaks" an intermittent fast, so this page sticks to what they do say.
What the sources say
| Source | What it says |
|---|---|
| University of Florida, Time to Eat pilot (ClinicalTrials.gov) | Participants may have calorie-free beverages, water, tea, black coffee or sugar-free gum during the fasting period. |
| University of Bath intermittent fasting study (ClinicalTrials.gov) | During fasted cycles, participants only consume water and black tea or coffee, with no milk or sugar. |
| CDC | Plain coffee and tea are low-calorie choices; sweetened coffee and tea contain calories. |
| MedlinePlus, fasting for a blood test | Plain water only. Coffee can affect your results. |
Those are study protocols, not health advice: they show what researchers chose for their participants. They don't prove coffee has no effect on a particular goal. The Florida record (NCT03590847) is a 4-week pilot with 10 adults aged 65 and older who have overweight and limited mobility. The Bath record (NCT02498002) enrolled adults aged 18 to 65, lean and with overweight.
What to put in the cup
- Black coffee, plain tea: what the two protocols describe. Bath specifies tea without milk or sugar.
- Sugar, syrups, sweetened drinks: these add calories, per the CDC.
- Milk or cream: the Bath protocol excludes milk; none of the sources used here covers cream or a splash of either.
- Sugar-free gum: Florida's protocol allowed it. Bath's allowed only water and black tea or coffee, which leaves it out.
When the answer is no
If a doctor asked you to fast for a blood test, the rules are stricter. MedlinePlus says to have only plain water for several hours (usually 8 to 12) and not coffee, because beverages like coffee can get into your bloodstream and affect results. Follow your provider's instructions for the exact time.
If your doctor told you to fast in a specific way, that beats anything here. When Harvard Health says time-restricted eating appears safe for most people, it excludes people with diabetes, people with eating disorders, pregnant or breastfeeding people, and people who need to take medication with food. Fasting Timer's own disclaimer also asks anyone under 18 to talk to their doctor before fasting. Talk to your doctor before fasting.
How much caffeine
The FDA cites 400 milligrams a day, about two to three 12-ounce cups of coffee, as an amount not generally associated with negative effects for most adults. Some conditions and medications make people more sensitive to caffeine. If you're pregnant, trying to become pregnant or breastfeeding, the FDA recommends talking to your health care provider.
Fasting with Fasting Timer
Fasting Timer doesn't track coffee, calories or ingredients, and it doesn't tell you what breaks your fast. You decide that, using what's above. What it does is track the time:
- Open the Timer tab, pick a plan from the plan chip (the daily plans, from 12:12 to OMAD, are free) and tap Start fasting.
- Watch the ring and the Started and Goal boxes to see how long you've gone and when you'll finish. If you forgot to start it, tap Started to open Edit start time.
- Use the Water today card to log a glass of water with the + button.
- You'll get a notification when the fast is complete and one when there's an hour to go.
If you're planning a longer one, read how to do a 24 hour fast first.
Fasting stages are general information, not medical advice. Talk to your doctor before fasting, especially if you are pregnant, have diabetes or another medical condition.
FAQ
- Does black coffee break a fast?
- None of the sources used here defines it. Two registered fasting studies, one at the University of Florida and one at the University of Bath, allowed black coffee during fasting hours. For a fast before a blood test, MedlinePlus says to have only plain water and that coffee can affect your results.
- Can you have sugar in coffee while fasting?
- Sugar adds calories. The CDC notes that sweetened coffee and tea contain calories. The Bath protocol allowed black tea or coffee with no milk or sugar.
- Can you drink tea while fasting?
- The Florida protocol allowed tea during the fasting period, and the Bath protocol allowed black tea with no milk or sugar.
- Can you drink coffee before a blood test?
- Not if your provider told you to fast for it. MedlinePlus says juice, coffee, soda and other beverages can get in your bloodstream and affect results, so have only plain water. If you aren't sure whether your test needs fasting, ask your provider.
- How much caffeine is too much?
- The FDA cites 400 milligrams a day, about two to three 12-ounce cups of coffee, as an amount not generally associated with negative effects for most adults. If you're pregnant, trying to become pregnant or breastfeeding, it recommends talking to your health care provider.
Sources
- ClinicalTrials.gov NCT03590847: Time to Eat Study - Pilot (University of Florida)
- ClinicalTrials.gov NCT02498002: Impacts of Intermittent Fasting in Adults on Energy Balance (University of Bath)
- CDC: Water and Healthier Drinks
- MedlinePlus: Fasting for a blood test
- FDA: Spilling the Beans: How Much Caffeine Is Too Much?
- Harvard Health: Should you try intermittent fasting for weight loss?