Does Coffee Break a Fast? Black, Milk, Latte and Bulletproof

By Mustafa Tarabya, founder of DT Nova · Published 25 October 2026

Plain black coffee does not break an intermittent fast, but milk, cream, sugar, butter and most syrups do, because they add calories. The one exception runs the other way: if you are fasting for a blood test, even black coffee is out.

Cleveland Clinic lists black coffee as acceptable when fasting, and every calorie number below is arithmetic from USDA FoodData Central. Below are an order-by-order table, six worked examples with clock times, and the blood test rule. Written by Mustafa Tarabya, founder of DT Nova, the studio that makes FastTrack.

Medical note: This is general information, not advice for you. Ask a clinician before fasting if you are pregnant or breastfeeding, or have diabetes. The same goes for medication that must be taken with food, or a history of an eating disorder. If your fast is for a lab test, the instructions from whoever ordered the test override this page.

The coffee order table, drink by drink

The table uses one rule, quoted from Cleveland Clinic's intermittent fasting guide: "To maintain a fasting state, you must not consume any foods or drinks with calories." The calories are USDA's figure per 100 g multiplied by the portion USDA lists for that food.

Coffee order by order: does it break a fast?

Order	Calories, USDA arithmetic	Verdict	Why
Black brewed coffee, 8 fl oz (237 ml)	About 2.	Does not break it.	Cleveland Clinic lists black coffee as acceptable.
Espresso, one 1 fl oz (30 ml) shot	About 3.	Does not break it.	Same drink, smaller cup.
Black coffee with 1 tbsp (15 ml) whole milk	About 12.	Breaks a strict fast.	Any calories count under the rule.
Black coffee with 1 tbsp (15 ml) half and half	About 22.	Breaks it.	Dairy fat and milk sugar.
Black coffee with 1 tbsp (15 ml) heavy cream	About 53.	Breaks it.	Mostly fat, still calories.
Black coffee with 1 tsp sugar	About 19.	Breaks it.	Pure sugar.
Latte, double shot with 8 fl oz (237 ml) whole milk	About 154.	Breaks it.	That is a small meal.
Latte, double shot with 8 fl oz (237 ml) oat milk	About 115.	Breaks it.	Plant milk has calories too.
Bulletproof: coffee, 1 tbsp butter, 1 tbsp coconut oil	About 225.	Breaks it.	Over 200 calories of fat.
Black coffee with a zero-calorie sweetener	Under 5 per serving on the label.	Gray zone.	Cleveland Clinic says sweeteners can end a fasting state.

The USDA records behind those numbers, per 100 g:

Brewed coffee: 1 kcal, with a cup listed as 237 g.
Espresso: 9 kcal, with 1 fl oz listed as 29.6 g.
Whole milk: 61 kcal, 15 g per tbsp, 244 g per cup.
Half and half: 131 kcal. Heavy cream: 340 kcal, both 15 g per tbsp.
Granulated sugar: 387 kcal, 4.2 g per tsp.
Oat milk: 45 kcal, 244 g per cup.

The free FastTrack timers (16:8, 18:6 and 20:4) show a live countdown, so you can see if the latte lands inside your window. Premium adds custom windows, OMAD, the stage timeline and statistics.

Why black coffee passes and milk does not

The same Cleveland Clinic guide names the drinks that keep you fasting: "Zumpano says water, carbonated water, black coffee and unsweetened teas are all acceptable when fasting." A cup of black coffee at about 2 calories is as close to zero as a drink gets.

Milk is where the arguing starts. You will see a rule online that anything under 50 calories keeps you fasting. I could not find a medical source for that number, so this page does not use it. The only threshold with a source behind it is zero.

Worked days on a 16:8 schedule

The black coffee morning

Most people only need this one. Coffee before noon stays black, and the milk waits for the window. The full set of 16:8 timetables is in the 16:8 intermittent fasting schedule guide.

16:8 with black coffee, eating 12 pm to 8 pm

8:00 pm: last bite of dinner. The 16-hour fast starts.
7:00 am: black coffee, 8 fl oz (237 ml). About 2 calories. Still fasting.
8:30 am: a glass of plain water, 8 fl oz (237 ml).
10:00 am: second black coffee, 8 fl oz (237 ml). Still fasting.
12:00 pm: 16 hours done. First meal, plus milk in your coffee if you want it.
8:00 pm: the window closes and the next fast starts.

The latte moved into the window

The fast was going fine until the barista asked oat or whole. That was not a milk question. That was a 115-calorie question. The fix is not giving up the latte. It is moving it.

16:8 for latte drinkers, eating 10 am to 6 pm

6:00 pm: dinner ends. The fast starts.
6:30 am: a black espresso or black coffee while you wake up.
10:00 am: 16 hours done. The latte is part of breakfast, about 154 calories with whole milk.
2:00 pm: a second milk coffee if you like it. You are inside the window.
6:00 pm: the window closes. Black coffee only from here.

Bulletproof coffee, by the numbers

Bulletproof coffee is coffee blended with butter and an oil. USDA's records used here have no entry called MCT oil, so the math below uses coconut oil instead.

Bulletproof coffee as breakfast, not as a fasting drink

The cup: 8 fl oz (237 ml) coffee, 1 tbsp butter, 1 tbsp coconut oil.
Salted butter: 717 kcal per 100 g, 14.2 g per tbsp, so about 102 calories.
Coconut oil: 892 kcal per 100 g, 13.6 g per tbsp, so about 121 calories.
Coffee: about 2 calories.
Total: about 225 calories. It breaks the fast.
The fix: drink it at 12:00 pm as the first thing in your eating window, and count it as the meal it is.

Sweeteners, creamers and "zero calorie" labels

Cleveland Clinic's advice on sweeteners is direct: "Artificial sweeteners, like saccharin, aspartame and sucralose, have the potential to remove you from a fasting state." The label adds a second problem.

Under the FDA labeling rule in 21 CFR 101.60, a product can say "zero calories" when it contains "less than 5 calories per reference amount customarily consumed". Zero on the front means under 5 per serving, not nothing.

Reading a zero-calorie creamer label at 7 am

Serving on the label: 1 tbsp (15 ml), "0 calories".
What the rule allows: under 5 calories per serving.
You pour three servings, 3 tbsp (45 ml): up to just under 15 calories.
Strict fast: it breaks it, or at least you cannot prove it does not.
Relaxed fast: gray zone. Cleveland Clinic says to avoid or limit sweeteners.
Cleaner swap: black coffee now, the creamer at 12:00 pm when the window opens.

The blood test exception

A fast for blood work has stricter rules. Labcorp says that if your provider recommended fasting, you "should avoid coffee even if it’s black with no sugar or cream." Its reason is that caffeine "can stimulate digestive processes that may alter certain readings." The full guide is fasting before blood work.

Coffee on a blood test morning, draw at 8:00 am

8:00 pm the night before: last meal. That is 12 hours before the draw, the top of the 8 to 12 hours Labcorp lists.
After 8:00 pm: plain water only. No coffee, no tea.
6:30 am: water, not coffee. Labcorp says "Plain water is always encouraged."
8:00 am: the blood draw.
8:15 am: first coffee, any way you like it. Labcorp says your fast is over once the draw is complete.

How much coffee during a fast

Black coffee is allowed, not unlimited. The FDA cites 400 milligrams a day for most adults, "about two to three 12-fluid-ounce cups of coffee". It lists regular brewed coffee at 113 to 247 milligrams per 12 fl oz (355 ml). Coffee also counts toward your fluids, which the WaterDrop guide does coffee count as water covers.

A 20:4 day with two black coffees and a tea, eating 4 pm to 8 pm

8:00 pm: last meal. The 20-hour fast starts.
7:00 am: black coffee, 12 fl oz (355 ml).
11:00 am: black coffee, 12 fl oz (355 ml).
Caffeine so far by FDA's range: 226 to 494 milligrams. The top of that range is past 400.
2:00 pm: unsweetened black tea instead of a third coffee. FDA lists black tea at 71 milligrams per 12 fl oz.
4:00 pm: 20 hours done. The window opens.

If the morning coffee comes before you remember to start a timer, FastTrack lets you edit a past fast, including a wrong start time.

Questions people ask

Can you drink a latte while fasting?

Not without ending the fast. A double shot with 8 fl oz (237 ml) of whole milk is about 154 calories by USDA figures. That is a small meal. Drink the espresso black while you fast, and order the latte as the first thing in your eating window.

Can I drink diet soda while fasting?

Diet soda is usually labeled zero calories, which under the FDA rule means under 5 per serving. Cleveland Clinic still advises avoiding or limiting artificial sweeteners such as aspartame and sucralose, which it says can remove you from a fasting state. Water, sparkling water, black coffee and unsweetened tea are the cleaner choices.

What can I put in my coffee that won't break my fast?

Nothing with calories. That leaves black coffee, espresso, ice and water. Sweeteners labeled zero calories can still carry under 5 per serving under the FDA labeling rule, and Cleveland Clinic advises limiting them. Milk, cream, sugar, butter, oil and sugared syrups all add calories and end a strict fast.

Does flavored coffee break a fast?

It depends on where the flavor lives. If the bag's nutrition label shows 0 calories for brewed coffee, flavored beans drunk black behave like black coffee. Sugared syrups break the fast. Syrups labeled zero sit in the sweetener gray zone, because zero can mean under 5 calories per serving. Read the serving size, not only the front.

Sources

Guides

A 16:8 intermittent fasting scheduleA 16:8 intermittent fasting schedule with clock times for early risers, 9-to-5, night shifts and weekends, a 12:12 ramp-up week and what the evidence says.
A fasting app without a subscription wallLooking for a fasting app without a subscription? What a free intermittent fasting tracker should include, the traps, and what FastTrack keeps free.
Fasting before blood workFasting before blood work: which tests need it, the hours Labcorp, Quest and MedlinePlus give, and seven timelines from your last meal to the draw.
A Zero fasting app alternativeLooking for a Zero fasting app alternative? What Zero includes free and in Zero Plus, by its own App Store listing, next to FastTrack's free tier.