What Can You Drink While Fasting? The Complete List

Most fasting questions are not about food. They are about the cup in your hand at hour fourteen. Can you have coffee? Tea with honey? A splash of cream? A Diet Coke?

Below is every common drink with a verdict and the reason behind it. Where a published calorie figure exists, it is here. Where the honest answer is "it depends what you are fasting for", the page says so instead of pretending.

Quick answer: Water, black coffee and plain tea are safe during any fast. So is anything else with no calories in it. Anything with sugar, protein or fat breaks a fast, and that includes milk, cream, butter coffee, juice and smoothies. The real gray area is small: near-zero additions like lemon and vinegar, and calorie-free sweeteners, where the argument is about insulin rather than calories.

The complete list

For anything the table leaves out, the food and drink checker gives the same verdict for strict fasting, fat loss and autophagy separately.

How to read the verdicts

There is no single line where a fast breaks, because "breaking a fast" means three different things depending on why you are fasting.

A strict clean fast. Any calorie ends it. This is the only definition with a clean edge, and it is the one the "Yes" column above answers.

A fat-loss fast. What matters is whether the drink adds calories you meant to skip and whether it interrupts fat mobilisation. Under ten calories is not going to decide anything. Two hundred will.

An autophagy fast. The strictest bar and the one with the least human evidence behind it. Nobody can measure autophagy in a living person with a routine test, so anyone quoting you a hard cutoff is quoting a convention. Stick to water, black coffee and plain tea and stop guessing.

Gut rest. Water only. Coffee does not break a fast metabolically, but it does stimulate gastric acid and gut motility, which is exactly what you were trying to pause.

Fat in your coffee: the answer most people get wrong

This is the one readers argue about, and the argument always runs the same way: fat barely raises insulin, fasting works through insulin, so fat in coffee is free.

The first half is roughly true. The conclusion does not follow.

Start with the arithmetic

USDA's published values, per tablespoon:

Black coffee is genuinely free at about 2 calories a cup. Everything else on that list is not. The original butter coffee recipe calls for one to two tablespoons of butter plus one to two tablespoons of MCT oil, which lands between roughly 220 and 445 calories — more than a bowl of cereal, drunk by someone who believes they are fasting. USDA has no analysed entry for MCT oil, so coconut oil above is the closest published stand-in; MCT oil is essentially pure fat and sits in the same range.

Note the ranking, because it surprises people. Half-and-half sounds like the indulgent choice and heavy cream sounds like the disciplined one. Per tablespoon, heavy cream carries two and a half times the calories.

Fat is quieter than carbohydrate, not silent

In 1983, Collier and O'Dea gave subjects 50 g of butter alongside carbohydrate or protein and measured the response. Blood glucose was lower with the fat present, as you would expect. The insulin response was not reduced. The authors described it as a potentiation of insulin secretion in the presence of fat.

Dairy adds a second wrinkle. In a 2001 study in the American Journal of Clinical Nutrition, Ostman and colleagues found milk products with glycemic indexes of 15 to 30 — very low — and insulinemic indexes of 90 to 98, on par with white bread. Dairy raises insulin out of all proportion to its sugar.

Read the mechanism before you apply it, though: the driver is dairy protein, and cream has the least protein per calorie of any dairy product. The effect is real. The dose in one tablespoon of cream is not. Which is why the calorie column, not the insulin column, is the one that should decide your coffee.

A high ketone reading is not proof of a deeper fast

MCT oil does raise blood ketones, and people take that as evidence the fast is intact. It is not evidence of anything about where the ketones came from. Work on exogenous ketone drinks found they raised blood ketones sharply while lowering free fatty acids, from about 0.7 to 0.4 mmol/L — the authors concluded the drinks inhibit fat release from adipose tissue. In a real fast, ketones are high because you are breaking down your own fat. After a ketone drink, they can be high while fat release is suppressed. A meter cannot tell the two apart.

That study used ketone esters rather than butter coffee, so it is not a direct test. The lesson still transfers: a number on a meter is not a verdict on your fast.

Nobody pours one tablespoon

Every figure above is per tablespoon, and a tablespoon in a twelve-ounce mug is almost invisible. A generous splash is commonly two to four. At heavy cream that is 100 to 200 calories, three times a morning.

Measure your normal pour once, into an actual spoon. The number tells you whether this conversation is about 20 calories or 200. If it is 200, that is not a coffee problem, it is most of the deficit you built by skipping breakfast.

The practical version. Fasting strictly or for autophagy: black. Fasting for fat loss and you want it to taste like something: one measured tablespoon of half-and-half, in one coffee rather than four. Want flavour for nothing: cinnamon, or a strip of orange peel. Having butter coffee anyway: fine, but log it as your first meal and start the fasting timer when the cup is empty.

Diet soda and calorie-free sweeteners

Zero calories, so under a calorie definition diet soda does not break a fast. The objection is different: sweet taste with no sugar behind it may still prime an insulin release, the cephalic phase response. Whether it does depends on the sweetener and the person.

What the evidence looks like, sweetener by sweetener. Aspartame studies are mixed — some show a modest response, some none. Sucralose has the strongest case against it: a 2013 study in Diabetes Care by Pepino and colleagues found sucralose raised insulin by around 20 percent in subjects with obesity despite carrying no calories. Acesulfame potassium is usually blended with sucralose and the human data is thin. Stevia looks close to inert.

There is a second concern that has nothing to do with insulin. Suez and colleagues reported in Cell in 2022 that sucralose and saccharin alter gut microbiome composition with regular use. If gut rest is why you fast, diet soda works against it.

So: one can during a fat-loss fasting window is very unlikely to matter. Four cans across a fasting window is a different habit, and if you are fasting for insulin sensitivity or autophagy the uncertainty is not worth buying. Plain sparkling water gives you the same cold fizzy ritual with none of the argument.

Lemon, vinegar and the near-zero additions

A squeeze of lemon adds roughly 1 to 3 calories. It will not trigger an insulin response worth the name, and it makes plain water drinkable, which matters more than the purity does. Half a lemon is still fine. A whole lemon in every glass all morning stops being a squeeze.

Diluted apple cider vinegar sits in the same place — a tablespoon or two in water costs almost nothing.

What ruins both is what people stir in afterwards. Honey is the usual culprit, at about 64 calories a tablespoon. Sugar and maple syrup are the same story. Mint, ginger, cucumber and salt are all genuinely free.

One non-fasting note on lemon: citric acid erodes enamel. Use a straw, rinse with plain water, and do not brush for half an hour afterwards.

Water and electrolytes

Water is the thing that decides whether your fast is comfortable. Dehydration causes most of the common fasting side effects people blame on fasting itself — headaches, fatigue, dizziness. You lose more water and more minerals than usual during a fast, especially in the first week of a new routine.

Aim for two to three litres a day, more if you train or live somewhere warm, and put a number on it with the daily water target calculator. Dark urine, a headache and a short temper are the signs you are behind.

Water alone is not the whole job. Most people drink plenty and skip electrolytes entirely, then blame the headache on the fast. A pinch of salt helps absorption and costs nothing; the electrolyte calculator sets a daily amount for sodium, potassium and magnesium based on your weight and how long you go.

Common mistakes

Treating "just a splash" as nothing. It is the single largest source of accidental calories in a fasting window, and it is invisible because it arrives four tablespoons at a time.

Trusting the front of the bottle. Flavoured waters, bottled teas and café drinks hide sugar and sweeteners routinely. A bottled green tea can carry as much sugar as a soft drink.

Skipping electrolytes. See above. Most fasting headaches are mineral, not moral.

Too much caffeine on an empty stomach. Caffeine absorbs faster with no food in the way. Three cups fasted can feel like five, and the cortisol bump can make you hungrier rather than less. One or two cups in your fasting window, and nothing after early afternoon if you want to sleep.

Ordering by name. A black americano is fine. A latte, a cappuccino, a chai latte and a mocha are meals with coffee in them.

How Fasted Helps

Fasted carries the same verdicts inside the app, so you can check a drink without opening a browser at hour fourteen. The timer shows where you are in your fasting window. It will not count the cream for you — the app logs no food and no drinks, only a daily protein and fibre entry in grams — so whether the splash was ever really a splash is still a judgement you make.

Frequently Asked Questions

Does black coffee break a fast?

No. USDA lists an 8-ounce cup of brewed coffee at about 2 calories. It triggers no meaningful insulin response and is the most widely accepted fasting drink there is. Everything in the coffee debate is about what you put in it.

Does bulletproof coffee break a fast?

Yes. A standard cup is 220 to 445 calories from butter and MCT oil, which breaks a fast under any calorie-based definition. The "fat does not raise insulin" defence does not rescue the arithmetic — those calories still count against a fat-loss deficit. Butter coffee is a fine low-carb breakfast. It is not a fasting aid.

Does a splash of cream break a fast?

Under a strict fast, yes. Under a fat-loss fast, one measured tablespoon of heavy cream is 51 calories and changes very little — as long as it stays one tablespoon. In a large mug a "splash" is often three or four, which is 150 to 200 calories.

Does lemon water break a fast?

Not in any practical sense. A squeeze is roughly 1 to 3 calories, too little to raise insulin or interrupt fat burning. Skip it only if you are keeping a strictly water-only fast for religious or therapeutic reasons.

Does green tea break a fast?

No. Plain green tea is brewed leaves and water with no meaningful calories. Its main polyphenol, EGCG, is studied for effects on fat oxidation and the same AMPK and mTOR pathways fasting acts on, so if anything it works with the fast. A café matcha latte is a different drink entirely.

Does diet soda break a fast?

Not on calories. The open question is whether the sweeteners prime an insulin release, and the answer varies by sweetener and person. For a casual or fat-loss fast, one can is unlikely to matter. For insulin sensitivity or autophagy, plain sparkling water is the cleaner choice.

Can I drink coffee with stevia while fasting?

Stevia carries no calories and appears to have little effect on blood glucose. For fat-loss fasting it is likely fine. For autophagy, go without. Check the packet too — many tabletop stevia products are mostly bulking agent.

Will a splash of almond milk break my fast?

Unsweetened almond milk is low but not zero. It breaks a strict fast. For fat loss a small splash is unlikely to matter, and the same warning applies as with cream: measure what you actually pour.

Can I drink energy drinks while fasting?

Sugar-free versions carry no calories but usually bring sweeteners, amino acids and a large caffeine dose to an empty stomach. Black coffee or green tea does the same job with less to argue about.