Can You Have Juice On A Fast? | Fasting Drink Rules

Fasting sounds simple: don’t eat for a block of hours, eat later, repeat. The first hard moment is never hunger. It’s thirst. You grab orange juice, apple juice, or that pricey cold-pressed green bottle and pause. Will that drink ruin the fast you worked for all night?

Here’s the straight answer. In most science-based fasting styles — like time-restricted fasting for fat burn or blood sugar control — juice counts as food. Mayo Clinic describes intermittent fasting as cycling between a normal eating period and a period with “very few or no calories.” Cleveland Clinic adds that to stay in a fasting state, you skip drinks with calories and stick with water, plain carbonated water, black coffee, or unsweetened tea. Juice almost never fits that rule because even 100% fruit juice delivers energy and sugar that tell your body, “We’re eating now.” A basic 8-ounce pour of orange juice lands around 110–120 calories and more than 20 grams of natural sugar.

That said, there is a twist: some people use the word “fast” to mean a juice cleanse, where juice is the only thing they drink all day. In that case, yes, you’re “having juice on a fast” — but that’s a totally different plan than classic intermittent fasting.

Why Drinks Matter During A Fast

During a fasting window, the goal is usually one of three things: tapping stored body fat, calming appetite swings tied to blood sugar spikes, or giving digestion a break. Mayo Clinic describes this as eating on a timed schedule, then switching to a stretch with “very few or no calories.” In that low-calorie stretch, your body starts leaning on stored fuel. Some people even reach mild ketosis, where fat becomes the main energy source.

Liquid calories count. Cleveland Clinic dietitians point out that to keep the fast going, you skip any drink with calories. Water, mineral water, black coffee, and plain tea all get a pass. Juice does not. Juice wakes digestion, raises blood sugar, and pulls you out of that low-insulin state you were trying to hold.

A common myth says, “Juice is fine because it’s liquid, not solid.” That’s marketing, not fasting science. Fasting is about energy — not chewing.

Juice While Fasting: Rules And Grey Areas

Not every fast follows the same rules. Some plans are strict “water only.” Some allow black coffee. Some are really juice diets using the word “fast.” The table below shows how different fasting styles treat juice so you can match your goal to the rule set you’re actually following.

Fasting Style	Main Goal	Juice Allowed?
Time-Restricted Fasting (16:8, etc.)	Fat burn and steadier blood sugar between meals	No during the fasting window, because juice has calories and sugar.
Water Fast / “Nothing With Calories” Fast	Gut rest, cell cleanup, steady insulin break	No. Only water, plain mineral water, black coffee, and unsweetened tea.
Religious Fast (varies by tradition)	Spiritual discipline and self-control	Rules vary. Some plans ban all food and drink for set hours, so juice would break that fast instantly.
Juice Cleanse / “Juice Fast”	Short, low-solid-food reset pushed for fast weight drop	Yes, because juice is the meal in this plan — but this is not a true zero-calorie fast.

Time-Restricted Fasting Windows

In a time-restricted setup like 16:8, you eat inside an eight-hour window and avoid calories the other 16 hours. Mayo Clinic and Cleveland Clinic both frame the fasting block as “no calories,” except water and other zero-calorie drinks. Juice does not pass that test. Even a small sip ends the fast because sugar and calories kick digestion back on.

People who fast this way tend to care about fat burn and steadier energy. They’re trying to keep insulin low between meals, which tells the body to pull from stored fat. Juice drives insulin back up because fruit sugar hits fast.

Strict Water Fasts

A strict water fast means water only, sometimes plain black coffee or plain tea with nothing in it. The idea is to let digestion rest and let the body run off stored fuel for a stretch. Juice ends that instantly. Even celery juice has calories, some sugar, and even a little protein.

Religious Fasts

Religious fasting rules are about devotion, not body composition. Some fasts forbid any liquid during daylight. In that setup, juice is off the table along with water. Other traditions allow drinking but still treat anything calorie-dense as a meal. In those cases juice usually breaks the practice too.

Juice Cleanses

A juice cleanse is often sold as a “detox fast.” You skip solid food and drink only produce juice for a day or more. Cleveland Clinic dietitians warn that this can drop calories so low that the number on the scale falls fast — but that first drop is mostly water and muscle, not body fat. Low fiber, low protein, and constant sugar swings can leave you light-headed, drained, and craving real food.

This is why wording matters. During a juice cleanse you are drinking juice “on a fast,” but that plan is not the same thing as skipping calories for metabolic, insulin, or gut rest reasons.

What Counts As Breaking A Fast Biologically

Now let’s talk biology. When does a fast actually end? Short answer: the second meaningful calories land.

Calories Wake Up Digestion

Verywell Health states that in the strict sense, “any intake of calories — whether from food or drink — breaks a fast.” That means juice, soda, milk, or a blended fruit smoothie all count as eating. Orange juice alone carries triple digits of calories per cup along with natural sugar. After that hit, your stomach and intestines get back to work and the clean break you were holding is gone.

Sugar Signals Insulin

Juice is mostly carbohydrate. An 8-ounce pour of orange juice or apple juice usually brings 20–27 grams of carbs, most of it as fast sugar. Sugar pushes insulin up. Mayo Clinic and Cleveland Clinic both point out that one draw of intermittent fasting is a drop in insulin between meals, which can push the body toward fat use and steadier blood sugar. A glass of juice ends that low-insulin stretch right away.

Protein Counts Too

Fruit and veggie juices carry more than sugar. Many give you 1–2 grams of protein per cup. That protein still “feeds” the body. From a strict fasting point of view, that means you’re no longer in a true fast.

Are There Any Loopholes?

Some people follow a softer style: tiny calorie wiggle room. A teaspoon of heavy cream in coffee. A squeeze of lemon and a pinch of salt in water. Plans like that aim for comfort, not lab-grade zero. Dietitians sometimes say this still “counts” for them if blood sugar barely moves. Juice rarely fits that middle ground. Fruit sugar isn’t tiny. It’s a full hit.

Bottom line so far: in nearly every fasting style built around fat burn, blood sugar control, or digestive rest, juice ends the fast.

Real Juice Numbers: Sugar And Calories

The next table shows rough nutrition for 8 ounces (about 240 ml) of common juices. These numbers come from USDA FoodData Central and other nutrition databases. Use it as a quick gut check before you pour.

Juice (8 fl oz)	Calories (kcal)	Sugar (g)
Orange Juice, 100%	110-120	20-22
Apple Juice, 100%	110-115	23-24
Green Juice Blend (celery, cucumber, kale, apple)	75-85	14-18
Plain Celery Juice	30-35	3-4

Even the lightest option on that list, straight celery juice, still lands 30+ calories per cup. The sweeter juices act more like a mini snack. A big juice-bar “small” can run 12–16 ounces, which can push past 200 calories and 40 grams of sugar in minutes. That is more sugar than many cans of soda.

The other snag: juice has almost no fiber. Fiber in whole fruit slows the sugar rush and helps you feel full. With juice, that brake is gone. The spike-and-crash that follows can make sticking to a fasting schedule tougher than it needs to be.

Better Drink Picks During The Fasting Window

If you’re inside the no-calorie block of a time-restricted fast or a water fast, stick with drinks that line up with medical guidance from Mayo Clinic, Cleveland Clinic, and other large health sources. Here’s what tends to work best.

Plain Water

Still water is always allowed in standard intermittent fasting plans outside medical procedures. Sip it through the whole fasting block. Staying hydrated helps cut headaches, low mood, and brain fog that some first-time fasters feel in the first week.

Sparkling Water Or Mineral Water

Unsweetened carbonated water gives flavor and fizz with no calories. Cleveland Clinic gives plain carbonated water a green light during a fast. Pick cans that show 0 calories, 0 sugar, and no fruit juice concentrate on the label.

Black Coffee

Black coffee carries almost no calories, which is why many intermittent fasting guides allow it. Caffeine can blunt appetite for some people and may nudge fat use for a short stretch. Skip milk, creamers, syrups, or sugar during the fast, because those extras turn coffee into a calorie drink.

Unsweetened Tea (Hot Or Iced)

Plain black, green, or herbal tea brewed in water lands near zero calories. That usually fits a fasting block unless your plan is absolute “water only.” Skip honey, sugar, and fruit juice shots. Sweeteners end the fast on the spot.

Lemon Water Or Salted Lemon Water

A squeeze of lemon in a tall glass of water adds almost no calories and gives a break from plain water taste. Many intermittent fasters view this as safe unless they’re doing an extreme water-only block. A pinch of salt in water is common on longer fasts to replace sodium and ease light-headed dips.

Medical fasts before surgery or lab work are a different story. Those usually call for strict “nothing by mouth” or “clear liquids only” rules for safety and clean test results. Always follow the exact fasting plan your care team gives you.

How To Use Juice Without Ruining Your Plan

Juice itself is not the villain. Pure orange juice and fresh green blends can deliver vitamin C, potassium, folate, and other micronutrients your body uses daily. The problem is timing and portion size, not the fact that juice exists.

Keep Juice For Your Eating Window

Pour juice after the fasting block is done for the day. During the eating window, that sugar hit isn’t “breaking” anything, because the fast is already over. Many people pour a 4–6 ounce glass of 100% juice next to a meal that includes protein (eggs, Greek yogurt, fish, lean meat). Pairing juice with protein and fiber slows the sugar spike and helps steady hunger.

Use Juice As A Side, Not The Whole Meal

Juice cleanses tend to promise fat loss, “detox,” and instant energy. Cleveland Clinic warns that these plans are low in protein and fiber, which can drain energy, break down muscle, and make cravings worse. Juice can live in a balanced diet, but a bottle of juice by itself all day long is not a balanced diet.

Watch The Pour Size

A standard juice-bar “small” can easily land 12–16 ounces. That can top 200 calories and 40+ grams of sugar in minutes. That sugar rush can set you up for a hard crash and a binge, which works against the steady rhythm people want from intermittent fasting.

Skip Juice During A Medical Fast Unless Cleared

Certain tests and procedures require a strict fast. Juice before a fasting blood draw can throw off lab numbers because the sugar hits the bloodstream fast. Ask your clinician which drinks are allowed before any test so your results stay accurate and your safety is protected.

Bottom line: if your goal is classic intermittent fasting — meaning no calories during the fasting block so your body leans on stored fuel and your blood sugar calms between meals — juice ends the fast. Juice still has a place in a day: pour it during the eating window, keep portions sane, and pair it with real food. For deeper reading on fasting rules and nutrient data, Mayo Clinic’s intermittent fasting FAQ and USDA FoodData Central give clear, source-level details. Mayo Clinic intermittent fasting FAQ and USDA FoodData Central