Does Celsius Break a Fast? Every Line, Label by Label

Does Celsius Break a Fast? Every Line, Label by Label

A 12 oz Celsius lists 10 calories, 0 g carbohydrate, 0 g sugar, and 200 mg caffeine, sweetened with sucralose. By calorie and carb count, it does not break an intermittent fast. But Celsius sells four product lines in 2026, not one, and two of them add carbs. On-the-Go sticks list 1 g carbohydrate; Celsius Hydration lists 1 g carb plus maltodextrin. If your goal is a strict zero-calorie or autophagy fast, plain water, black coffee, or tea is cleaner.

Below is every current Celsius line plus four other zero-sugar cans, checked against the three label lines that matter: calories, sweeteners, and amino acids.

Zero-Sugar Energy Drink Label Comparison

Sources: Celsius labels from celsius.com/products; Monster, Red Bull, and C4 from retailer nutrition panels; Alani Nu from alaninu.com. For a broader breakdown, see Celsius vs Monster label by label.

Does Celsius Break a Fast? Line by Line

Celsius.com lists four product lines in 2026: CELSIUS (Original), CELSIUS ESSENTIALS, CELSIUS ON-THE-GO, and CELSIUS HYDRATION. Older articles that reference HEAT or BCAA versions are working from discontinued listings.

Celsius Original (12 oz): 10 calories, 0 g total carbohydrate, 0 g sugar, 200 mg caffeine. The only sweetener is sucralose. By the informal "under 50 calories" rule used in intermittent fasting communities, it does not break a fast. (That 50-calorie threshold has no clinical trial behind it; for a goal-by-goal breakdown, see what breaks a fast.)

Celsius Essentials (16 oz): 10 calories, 0 g carbohydrate, 270 mg caffeine. Sucralose and acesulfame potassium. The ingredients list includes L-theanine, L-isoleucine, and L-leucine with no amounts printed. Those amino acids matter if autophagy is your goal. Label: "DO NOT EXCEED (1) SERVING PER DAY."

Celsius On-the-Go (powder stick): 10 calories, 1 g carbohydrate, 200 mg caffeine. Sucralose. One gram is minimal, but for a strict zero-carb fast it is not zero.

Celsius Hydration (powder stick): 15 calories, 1 g carbohydrate, 0 mg caffeine. The ingredients include maltodextrin (a fast-digesting carb filler) and sucralose. If you want electrolytes without breaking a fast, plain sodium, potassium, and magnesium in water are cleaner.

Do Energy Drinks Break a Fast? The Other Zero-Sugar Cans

The same three-part test applies to every zero-sugar can in the cooler.

Alani Nu (12 oz): 10 calories, 3 g carbohydrate, 200 mg caffeine. Sucralose and acesulfame potassium. Three grams of carbs ties Red Bull Sugarfree for the most among the 12 oz cans in this table, but it is still under 50 calories.

Monster Zero Ultra (16 oz): 10 calories, 6 g carbohydrate, 150 mg caffeine. Erythritol, a sugar alcohol, is among the first ingredients. The label does not say how much of those 6 g is erythritol. For a deeper look, see Celsius vs Monster label by label.

Red Bull Sugarfree (12 oz): 20 calories, 3 g carbohydrate, 114 mg caffeine. Sweetened with aspartame and acesulfame K. That 20-calorie count is the highest on this list. For more on aspartame during a fast, see aspartame and fasting.

C4 Energy Zero Sugar (16 oz): 5 calories, 0 g carbohydrate, 200 mg caffeine. But the formula includes CarnoSyn beta-alanine, L-citrulline, betaine anhydrous, and N-acetyl-L-tyrosine, relevant to autophagy fasters.

For contrast: a 16 oz Monster Original has 230 calories and 54 g of sugar. Sugared energy drinks break any fast, full stop.

Calories, Sweeteners, and Amino Acids: The Three Things That Matter

Calories and carbs

Every can in the table is 20 calories or under. All pass the informal "under 50 calories" rule. For a strict zero-calorie fast, none passes cleanly. That 50-calorie threshold is a community guideline, not a finding from a controlled trial.

Sweeteners

Most of these cans use sucralose. The evidence is not black-and-white.

A 2011 randomized crossover trial (Ford et al., European Journal of Clinical Nutrition, n = 8 healthy adults) found that sucralose ingestion did not raise GLP-1 or PYY, and sham-feeding sucralose produced no cephalic insulin response. A 2013 randomized crossover trial (Pepino et al., Diabetes Care, n = 17 adults with obesity) found that sucralose consumed 10 minutes before a glucose drink raised the peak insulin AUC about 20% compared with water. That was sucralose plus glucose, not sucralose alone.

A zero-sugar can taken by itself during a fast is unlikely to trigger a meaningful insulin response. Drinking it alongside food is a different question. For the full evidence, see the sucralose insulin studies. Red Bull Sugarfree uses aspartame instead; the evidence on aspartame and fasting follows similar lines.

Amino acids

Celsius Essentials lists leucine, isoleucine, and L-theanine. C4 lists beta-alanine, L-citrulline, and N-acetyl-L-tyrosine. None of these cans print the amounts.

mTORC1, a master growth regulator, senses amino acids (Wolfson and Sabatini, Cell Metabolism, 2017). That is the pathway strict autophagy fasters are trying to keep quiet. No study has tested the unprinted amino acid amounts in these cans on human autophagy. If autophagy is your priority, Celsius Original (no amino acids listed) is a safer pick than Essentials or C4.

Does Celsius Boost Fat Burning During a Fast?

Celsius markets itself around metabolism. The can carries this disclaimer: "CELSIUS® alone does not produce weight loss in the absence of a healthy diet and moderate exercise." For a closer look at the studies behind the brand's claims, see does Celsius actually burn fat.

Caffeine on an Empty Stomach: The Label Limits

A 12 oz Celsius delivers 200 mg of caffeine, or 16.7 mg per fluid ounce. Two cans equal 400 mg, which is the amount the FDA has cited as not generally associated with negative effects for most healthy adults (roughly two to three 12 oz cups of brewed coffee at 113 to 247 mg each, per the FDA). For caffeine across every Celsius size, see how much caffeine is in Celsius.

Celsius Essentials prints "DO NOT EXCEED (1) SERVING PER DAY." On-the-Go sticks say "DO NOT EXCEED (2) SERVINGS PER DAY." All Celsius labels warn the product is not recommended for people who are caffeine sensitive, children under 18, or women pregnant or nursing. Some people find 200 mg hits harder fasted. If that is you, starting with half a can is reasonable. For the full math, see the 400 mg daily math.

Zero-Calorie Caffeine Options for a Fasting Window

Caffeine per FDA and brand labels. For the salt side of a fasted morning, see do electrolytes break a fast.

So, Does Celsius Break Your Fast?

By calories and carbs, the 12 oz Celsius Original (10 calories, 0 g carbohydrate) does not break an intermittent fast under the informal 50-calorie rule. By sweetener, sucralose alone is unlikely to trigger a meaningful insulin response based on the available evidence. By a strict autophagy or zero-calorie standard, any flavored, sweetened can is a compromise compared with plain water or black coffee.

The answer depends on which fast you are running. Pick the goal first. The label follows.

Frequently Asked Questions

Can I drink Celsius while fasting?

Yes, for a standard 16:8 or OMAD intermittent fast. The 12 oz Celsius Original has 10 calories and 0 g carbohydrate, well under the commonly cited 50-calorie threshold. If your fast is strictly zero-calorie, any flavored energy drink is a slight compromise. Water, black coffee, and plain tea are technically cleaner.

Does Celsius kick you out of ketosis?

The 12 oz Celsius label lists 0 g total carbohydrate, so it adds no carbs to your daily count. That said, a label number is not a measured ketone result. If staying in ketosis matters, track your own levels rather than relying on any single product label.

Does Celsius Essentials break a fast?

Celsius Essentials has the same 10 calories and 0 g carbs as the Original, so it passes on calories. The difference: its ingredient list includes L-leucine, L-isoleucine, and L-theanine. Amino acids can activate mTORC1, which strict autophagy fasters want to avoid. Amounts are not printed, so you cannot quantify the effect.

Does Monster Zero Ultra break a fast?

Monster Zero Ultra lists 10 calories and 6 g carbohydrate per 16 oz can, with erythritol listed among the first ingredients. By the 50-calorie rule it technically passes. The 6 g of carbs is higher than any other zero-sugar can on this list, though the label does not say how much of it comes from erythritol, a sugar alcohol.

Does Celsius break a religious fast?

Yes. Ramadan and Yom Kippur fasts prohibit all food and drink, including water, during fasting hours. Any energy drink, coffee, pouch, or flavored beverage breaks a religious fast. Also skip energy drinks before a fasting blood draw, since caffeine and sweeteners can affect some lab results.

Is it OK to drink Celsius on an empty stomach?

Celsius delivers 200 mg of caffeine in 12 oz with no food to buffer it. The FDA cites 400 mg per day as an amount not generally associated with negative effects for most healthy adults. Some people tolerate 200 mg fasted without issue; others find it strong. If you are caffeine-sensitive, try half a can first and see how you respond.

Zero Calories, Smaller Dose, Longer Tail

Every zero-sugar energy drink in the table above delivers 150 to 270 mg of caffeine in one sitting. That is a strong dose on an empty stomach, and caffeine alone tends to fade in three to four hours.

Roon delivers 80 mg caffeine with 60 mg L-theanine, 25 mg methylliberine (Dynamine), and 5 mg theacrine (TeaCrine). Zero calories, zero sugar, sweetened with sucralose (same sweetener bucket as Celsius, same evidence applies). No liquid to finish.

Methylliberine supplies the duration. In a randomized, double-blind crossover PK study (n = 12), 100 mg methylliberine with 150 mg caffeine cut caffeine's oral clearance from 41.9 to 17.1 L/hr and extended its half-life from 7.2 to 15 hours, with no increase in peak concentration. That is 4x Roon's methylliberine and roughly 1.9x its caffeine, so the direction applies, not the exact numbers. The felt window is 6 to 8 hours, not 15. Stop at least 8 hours before bed.

Roon is not a fat burner, an autophagy tool, or a meal replacement. It breaks a religious fast like everything else on this page. For a standard intermittent fast, it is worth a look if 200 mg on an empty stomach feels like too much. From $9.16 per tin on the 12-tin subscription. Try Roon on your next fasted morning.

Written by Roon Team