How many calories are in a can of Celsius?

About 10 calories per 12 oz can, with 0 g of sugar. A few versions list up to 15 calories.

Does Celsius break ketosis?

No. It has no sugar and very few calories.

Is it safe to drink Celsius on an empty stomach?

Many people tolerate it, but 200 mg of caffeine without food can cause jitters, nausea or a fast heartbeat. Start with half a can if you are unsure.

Does Celsius help burn fat while fasting?

Caffeine slightly raises fat use and energy expenditure for a few hours. The effect is small and adds little to the fast itself.

Does Celsius Break a Fast? No

Reviewed by the FastTrack team · Updated June 2026

Short answer: No

Celsius does not break a fast for most goals. A 12 oz can has about 10 calories and no sugar, sweetened with sucralose. The bigger issue is its 200 mg of caffeine on an empty stomach.

Calories	~10 kcal per 12 oz can
Breaks a weight-loss fast?	No
Breaks ketosis?	No
Breaks autophagy?	Unlikely
Insulin impact	Minimal

Why a can of Celsius keeps you fasted

Ten calories with no sugar or protein is too little to raise insulin or interrupt ketosis. The caffeine, green tea extract and guarana are stimulants without meaningful energy, and caffeine slightly increases fat use for a few hours, so the drink fits inside a fasting window as far as the fast itself goes.

The caffeine is the catch

200 mg of caffeine is about two cups of coffee in one can. On an empty stomach it can cause jitters, a racing heart, stomach upset or an energy crash later. The label advises no more than two cans a day and recommends against it for people under 18, pregnant or nursing, or sensitive to caffeine. A can after 2 p.m. can also cost you sleep.

How much is safe

One can during the fast is a sensible limit, ideally in the morning with water alongside. Stay under the 400 mg of daily caffeine the FDA cites for healthy adults, counting coffee and tea too.

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Frequently asked questions

How many calories are in a can of Celsius?: About 10 calories per 12 oz can, with 0 g of sugar. A few versions list up to 15 calories.
Does Celsius break ketosis?: No. It has no sugar and very few calories.
Is it safe to drink Celsius on an empty stomach?: Many people tolerate it, but 200 mg of caffeine without food can cause jitters, nausea or a fast heartbeat. Start with half a can if you are unsure.
Does Celsius help burn fat while fasting?: Caffeine slightly raises fat use and energy expenditure for a few hours. The effect is small and adds little to the fast itself.