Can you drink Celsius while fasting?

Can you drink Celsius while fasting? Yes, most people can drink Original Celsius without breaking their fast. The Original Celsius has zero carbs, zero protein and only 10 calories. That puts it under the common “50 calorie rule” that most fasters follow to stay in a fasted state.

But it gets more complicated when you look at the other Celsius products and what your fasting goals are.

Does Celsius break intermittent fasting?

The Original Celsius does not break your fast for weight loss. It has zero grams of carbs, zero grams of protein and 10 calories per can. The “one gram rule” that many fasting experts recommend says you should stay under one gram total of carbs and protein combined. Original Celsius fits within this limit.

Celsius Heat and Celsius BCAA are different. These versions contain 2 grams of carbs per can. That goes over the one gram rule and could trigger a small insulin response.

Here is what each Celsius product contains and how it affects fasting.

1. Original Celsius has 0 grams carbs, 0 grams protein, 10 calories and 200mg caffeine. This one is safe for most fasting goals.
   
2. Celsius Heat has 2 grams carbs, 0 grams protein, 10 calories and 300mg caffeine. The carbs may break a strict fast.
   
3. Celsius BCAA has 2 grams carbs, 0 grams protein, 10 calories and 100mg caffeine. The BCAAs and carbs can trigger an insulin response.
   
4. Celsius Stevia uses stevia instead of sucralose and has similar stats to Original Celsius.
   

What happens when you drink Celsius during a fast?

When you drink Original Celsius during your fasting window, the 200mg of caffeine enters your bloodstream and tells your nervous system to wake up. Caffeine sends signals to your fat cells to break down stored fat. A systematic review of 94 studies confirmed that caffeine increases fat metabolism.

The caffeine also boosts your metabolic rate. A Mayo Clinic sports medicine specialist confirmed that any caffeinated drink will increase metabolism in the short term. About 100mg of caffeine burns roughly 100 extra calories per day.

Celsius also contains green tea extract, guarana seed extract and ginger root. Green tea extract provides additional caffeine and antioxidants. Guarana seeds have twice the caffeine concentration of coffee beans. These ingredients work together to create what Celsius calls their MetaPlus blend.

A university study found that participants who consumed Celsius burned an average of 100 more calories over a 3 hour period compared to those who drank a placebo.

Does sucralose in Celsius affect fasting benefits?

This is where things get complicated. Original Celsius uses sucralose as its sweetener. Sucralose has zero calories but research shows it may still affect your body during a fast.

A 2013 study gave 17 people either sucralose or water before a glucose tolerance test. Those who had sucralose showed 20% higher blood insulin levels. They also cleared the insulin from their bodies more slowly.

A 2018 randomized controlled trial found that 14 days of sucralose consumption decreased insulin sensitivity by 17.7% compared to the control group.

Scientists believe sucralose triggers something called “cephalic phase insulin release.” Your taste receptors sense the sweet taste and your brain tells your body to prepare for incoming sugar. This can cause a small insulin release even though no actual sugar arrives.

A 2020 study in Cell Metabolism found that consuming sucralose with carbohydrates reduced insulin sensitivity and blunted brain response to sweet taste. The effect did not happen when participants consumed sucralose alone.

For strict fasters who want maximum autophagy and cellular cleanup benefits, sucralose may not be ideal. For people fasting mainly for weight loss, the effect is small and probably will not derail your results.

What are the best Celsius options for fasting?

If you want to drink Celsius during your fast, stick with Original Celsius or Celsius Stevia. Both have zero carbs and zero protein.

Avoid Celsius Heat and Celsius BCAA during your fasting window. Save these for your eating window when you are exercising and need the extra energy.

Here are the rules for drinking Celsius while fasting.

1. Choose Original Celsius or Celsius Stevia
2. Limit yourself to one can during your fasting window
3. Save Celsius Heat and BCAA versions for your eating window
4. Drink plenty of water alongside your Celsius
5. Watch how your body responds and adjust if needed

What drinks are better than Celsius for fasting?

Black coffee and plain tea are the safest caffeine options during a fast. They have almost zero calories and do not contain artificial sweeteners.

Black coffee has 3 to 5 calories per cup and provides 80 to 100mg of caffeine. A 2014 study in Cell Cycle found that both regular and decaf coffee trigger autophagy due to their polyphenols. Coffee also suppresses appetite by stimulating the central nervous system.

Green tea provides 30 to 50mg of caffeine per cup plus a compound called EGCG. This compound helps burn fat and reduce inflammation. The caffeine in green tea releases more slowly than coffee, giving you steady energy without jitters.

Water with a pinch of sea salt can help with electrolytes during longer fasts without adding any calories or sweeteners.

Why does intermittent fasting work?

Intermittent fasting works by keeping insulin levels low. When you stop eating, your body switches from burning the sugar in your blood to burning stored fat for fuel.

A review of multiple studies found that intermittent fasting reduces insulin resistance and fasting insulin levels, especially when weight loss occurs. Insulin resistance increases your risk of type 2 diabetes, polycystic ovary syndrome and fatty liver disease.

When you fast for 12 to 16 hours, your body also starts a process called autophagy. This is your body’s built in cleanup system. It breaks down damaged cells and recycles them into new healthy cells. Research from animal and cellular studies suggests autophagy may help reduce inflammation and prevent damage to healthy tissue.

The metabolic switch from sugar burning to fat burning typically happens after 12 to 24 hours of fasting. During this time, your liver runs out of stored glycogen and starts converting fatty acids into ketone bodies for energy.

How does caffeine affect your fast?

Caffeine supports your fasting goals in three ways.

First, it suppresses appetite. A 2019 study in Nutrients found caffeine reduces hunger by stimulating the central nervous system. A 2022 study in Metabolism confirmed that caffeine decreases appetite perception during fasting.

Second, it increases fat burning. Caffeine tells your fat cells to release stored fat into your bloodstream where your body can burn it for energy. A 2017 study in Sleep Medicine Reviews found that caffeine increases metabolic rate and fat oxidation through adrenaline release.

Third, it may support autophagy. A 2010 study in Autophagy found that caffeine enhances autophagy in fasting states, speeding up cellular cleanup compared to fasting alone.

The FDA recommends adults keep their caffeine intake under 400mg per day. One can of Original Celsius has 200mg, so you could have two cans without going over the limit. Celsius Heat has 300mg per can, so one can is your limit if you want to stay within recommendations.

Too much caffeine can cause jitters, anxiety and disrupted sleep. These side effects work against your fasting goals because poor sleep increases hunger hormones and makes you more likely to overeat the next day.

Should you drink Celsius before a blood test?

No. Avoid Celsius and any caffeinated drinks before a fasting blood test. Caffeine stimulates your body, raises blood pressure, increases cortisol and releases fatty acids into your bloodstream.

A 2020 study in the British Journal of Nutrition found that drinking caffeine before a blood test affects markers beyond glucose. The researchers saw changes in lipid levels, inflammatory markers and hormone biomarkers.

For accurate bloodwork, drink only water unless your doctor says otherwise.

FAQ

Will Celsius break my fast for weight loss?

Original Celsius will not break your fast for weight loss. It has zero carbs, zero protein and only 10 calories. The 50 calorie rule allows small amounts of calories during fasting windows without disrupting fat burning. The caffeine in Celsius actually helps your body burn more fat.

Does Celsius spike insulin?

Celsius contains sucralose which may cause a small insulin response through taste receptor activation. A 2013 study found sucralose increased insulin levels by 20% compared to water. Original Celsius has zero actual carbs or sugar, so any insulin response would be minimal. For most people fasting for weight loss, this small effect will not change their results.

Can I drink Celsius Heat while fasting?

Celsius Heat contains 2 grams of carbs which goes over the one gram rule many fasters follow. If you are doing strict intermittent fasting, save Celsius Heat for your eating window. The 300mg of caffeine is also higher than Original Celsius at 200mg.

How many cans of Celsius can I drink while fasting?

Stick to one can during your fasting window. One Original Celsius has 200mg of caffeine. The FDA recommends staying under 400mg of caffeine per day. Too much caffeine can cause anxiety, jitters and sleep problems that work against your fasting goals.

Is Celsius better than coffee for fasting?

Black coffee is the safest choice for fasting because it has almost zero calories and no artificial sweeteners. Celsius provides more caffeine per serving at 200mg compared to coffee at 80 to 100mg per cup. Celsius also contains additional ingredients like green tea extract and guarana that may boost metabolism. The sucralose in Celsius is the main concern for strict fasters.

Will the artificial sweetener in Celsius mess up my fast?

Research on artificial sweeteners and fasting is mixed. Sucralose does not contain calories or carbs, so it will not directly break your fast. Some studies show sucralose may trigger a small insulin response through taste receptors. For weight loss fasting, this effect is small. For autophagy and cellular cleanup benefits, black coffee or tea may be better choices.

When should I drink Celsius during intermittent fasting?

Drink Celsius in the morning or early afternoon of your fasting window. The 200mg of caffeine will help suppress appetite and boost energy when you need it most. Avoid drinking Celsius within 6 hours of bedtime because the caffeine can disrupt your sleep.

Does Celsius help burn belly fat during fasting?

Caffeine from any source helps increase fat burning. A university study found Celsius helps burn an average of 100 extra calories over 3 hours compared to a placebo. Combined with the calorie deficit from fasting, this can speed up fat loss over time. No drink will spot reduce belly fat though. You lose fat from your whole body as you stay in a calorie deficit.

Can I add anything to my Celsius while fasting?

No. Celsius comes ready to drink and adding anything would likely break your fast. Adding milk, cream or sugar would add calories and spike insulin. The Original Celsius is already flavored and sweetened, so there is no reason to add anything.

Is Celsius keto friendly while fasting?

Yes. Original Celsius has zero carbs which fits within keto diet limits. Most keto dieters try to stay under 20 to 30 grams of carbs per day. One can of Original Celsius will not affect ketosis. Celsius Heat and BCAA versions have 2 grams of carbs each which is still low enough for most keto plans.

For those who prefer a simpler approach, explore whether black coffee is acceptable during a water-only fast. If muscle building is your priority, understanding which muscles are hardest to develop can shape your training focus. Compound movements accelerate progress—learn whether a 100kg deadlift is a respectable milestone.