Does Celsius Energy Drink Break a Fast?
Quick Answer
Most Celsius energy drinks will break your fast because they have carbs. The original Celsius has no carbs or protein, but it does have sucralose, which may still affect fasting benefits for some people. Celsius Heat and BCAA versions have 2 grams of carbs which is enough to go over the “one gram rule” many fasters follow. If you want to keep your fast as clean as possible, black coffee or tea is a safer bet for caffeine without messing with your fast.
Key Takeaways
- Original Celsius (zero carbs/protein) likely won’t cause an insulin spike
- Celsius Heat and BCAA versions (2g carbs) go over the fasting threshold
- Artificial sweeteners don’t usually spike insulin but may impact gut health
- 300mg caffeine in some Celsius drinks can cause energy crashes later
- Coffee and tea give you caffeine without breaking your fast
Celsius Energy Drinks and Fasting Impact
|
Celsius Version |
Carbs (g) |
Protein (g) |
Caffeine (mg) |
Likely to Break Fast? |
|
Original Celsius |
0 |
0 |
Varies (~200) |
No (but sweeteners may affect benefits) |
|
Celsius Heat |
2 |
0 |
300 |
Yes |
|
Celsius BCAA |
2 |
0 |
Varies (~200) |
Yes |
My friend Sarah swore by her morning Celsius during her 16-hour fasting stretch. “It gives me energy without food,” she said. But when her weight loss stopped, she started wondering if her go-to drink was quietly messing up her progress. This same question comes up all the time in fasting groups - can you drink Celsius and stay fasted? Let’s break it down with science and see what’s really going on.
What Breaks a Fast
The point of intermittent fasting is not just skipping meals but it’s keeping insulin low so your body switches from burning sugar to burning stored fat.
What triggers insulin the most? Mainly carbs and protein. Many fasting experts say if you stay under one gram total of carbs and protein combined (the “One Gram Rule”), you can keep the benefits of fasting.
That number isn’t exact for everyone. Your insulin sensitivity, health, and other factors play a role. But for most people, going over that tiny amount can start waking up insulin and interrupting the benefits.
Different foods and drinks have different effects:
- Carbs cause the biggest insulin spike
- Protein gives a smaller spike
- Fats barely affect insulin
- Caffeine alone doesn’t spike insulin but can raise cortisol
Celsius Ingredients
Celsius makes different drinks, and each one has a different nutrition profile.
The original Celsius has zero carbs and zero protein, according to its nutrition label. Sounds great for fasting. Until you notice it has sucralose which is an artificial sweetener.
The other versions are different:
Celsius Heat has 2 grams of carbs and a huge 300mg caffeine dose
Celsius BCAA also has 2 grams of carbs
Every version has their MetaPlus® blend, which includes:
- Taurine
- Guarana extract
- Caffeine (as caffeine anhydrous)
- Glucuronolactone
- Ginger extract
- Green tea leaf extract (15% EGCG)
They also have citric acid, natural flavors, and other additives depending on the flavor.
The Science Behind Celsius and Metabolism
Celsius promotes itself as a thermogenic drink which means that it can temporarily boost metabolism. On their site, they claim thermogenic drinks “increase metabolism” so your body burns more calories and fat even without exercise.
One study in the Journal of the International Society of Sports Nutrition found that Celsius increased resting energy expenditure (REE) and boosted fat breakdown.
Another study from the University of Oklahoma, published in the Journal of Strength and Conditioning Research, showed that men who drank Celsius before moderate workouts improved their body composition more than exercise alone.
A separate study compared Celsius to Diet Coke and found Celsius increased metabolic rate by about 13.8% after an hour, 14.4% after two hours, and 8.5% after three hours. Diet Coke didn’t do this.
For fasting, this matters because:
1. A higher metabolism may help burn more fat during a fast
2. But the ingredients that cause the boost could also break the fast
A 2020 study also found that drinking Celsius before exercise helped reduce body fat and improve endurance. But those benefits were tied to workouts and not fasting alone.
Artificial Sweeteners and Fasting
The original Celsius has sucralose, which is where things get tricky. Artificial sweeteners don’t usually spike insulin directly. So, from a strict insulin point of view, they don’t break a fast.
But research shows sweeteners might:
- Change gut bacteria
- Affect hunger hormones
- Trigger your body to prepare for sugar that never arrives
For some people, any sweet taste can cause cravings and make fasting harder. Others drink them without any problem.
Science isn’t fully settled, but many strict fasters avoid all sweeteners to get the most benefits, like autophagy (cell cleanup) and deeper metabolic changes.
Better Alternatives During a Fast
If you want caffeine without risking your fast, these are safer:
Black Coffee: Almost no calories, loaded with antioxidants, and may even boost autophagy during fasting.
Plain Tea: Green, black, or herbal teas give clean energy without breaking your fast. Green tea even has some of the same compounds as Celsius (like EGCG) but without the extras.
These drinks give you caffeine without the 300mg blast from Celsius Heat, which can help you avoid the big spike and crash.
For reference, coffee has around 80–100mg caffeine per cup, compared to up to 300mg in Celsius Heat. That slower, steadier caffeine release can help you stay fasted without feeling wiped later.
Caffeine Levels and Energy Crashes
One thing people forget is the crash. A study in the journal Nutrients found that high-caffeine energy drinks like Celsius can cause a big energy drop hours later.
That’s a problem if you’re fasting because the crash can lead to cravings. The same study confirmed Celsius raises resting energy expenditure, but the side effect is that crash - something you don’t want mid-fast.
If your main goal is sticking to your fast, coffee or tea’s moderate caffeine is usually a safer pick.
Can Celsius Help With Weight Loss Goals?
Some studies show Celsius can help with fat loss—if you pair it with workouts. In one study, people who drank Celsius before workouts for 10 weeks lost more body fat (-6.6%) than those who didn’t (-0.35%).
But those results were in people exercising and not fasting. The study’s authors pointed out that Celsius works best before a workout, not during a fasting period.
If weight loss is your main goal with fasting, you might get better results drinking Celsius during your eating window and before exercise.
Final Verdict: Does Celsius Break Your Fast?
Here’s the bottom line:
Original Celsius (Zero): From an insulin view, it shouldn’t break a fast. But sweeteners might still reduce some benefits.
Celsius Heat and BCAA Versions: These have 2 grams of carbs, so they’re likely to break a fast.
For Strict Fasting: Stick to black coffee or tea.
For Less Strict Fasting: If you care more about weight loss than deep fasting benefits, the original Celsius could be fine but coffee and tea are still better.
It comes down to your goals. For full fasting benefits like autophagy, skip Celsius. For weight loss with fasting, original Celsius might be okay but not perfect.
Frequently Asked Questions (FAQ)
Can I drink zero-calorie energy drinks during intermittent fasting?
Even with zero calories, these drinks have sweeteners and additives that may affect fasting benefits. Coffee or tea is still the safer choice.
Does caffeine break a fast?
Pure caffeine doesn’t break a fast from an insulin angle, but too much can raise stress hormones.
What drinks are definitely safe during fasting?
Water, black coffee, plain tea, and mineral water are always safe.
How does Celsius compare to other energy drinks for fasting?
Most energy drinks have ingredients that can mess with fasting. Celsius Zero is better than many, but sweeteners still make it less than ideal.
About the Author
This article was written by the Lifeboost writing team after reviewing clinical research on fasting, metabolism, and energy drinks. Our research included multiple scientific studies on Celsius and sweeteners. All facts are based on nutritional data and peer-reviewed studies as of 2024.
Disclaimer: This isn’t medical advice. Always talk to your doctor before making big changes to your diet or fasting routine, especially if you have health issues or take medication.
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