The truth nobody tells you about fasting
The simple answer to "what to drink during intermittent fasting?" fits in an elevator: drink calorie-free beverages as needed and make sure to replenish electrolytes, especially sodium.
That's the summary. But of course, people insist on delving deeper. Here's the detail almost no one tells you: during fasting, your body loses sodium like a young snake sheds its skin. (Spoiler: it's a lot.) If you only replenish water, you further dilute the sodium in your blood. And that's problematic.
But before we talk about electrolytes, there's something important to clarify: fasting is not binary.
Fasting is not "on" or "off"
People become almost religious about fasting. "Does a drop of honey break the fast? A cup of coffee with a little milk?"
Answer: it depends on the context. When you decide to "break" or "maintain" a fast, two factors matter:
- The amount of calories: the more calories you consume, the more likely you are to interrupt the fast.
- The type of calories: not all calories are equal. What matters is the insulin response.
From most to least metabolic disruption:
- Carbohydrates (especially refined sugars) → highest insulin release.
- Protein → moderate insulin response.
- Fats → minimal insulin response.
Carbohydrates trigger the highest insulin release, a hormone that tells your cells to store fat. Insulin suppresses ketosis—the state where most of the benefits of fasting occur—and disrupts mTOR suppression.
But a teaspoon of honey in your tea or in your electrolyte drink won't ruin your fast. Neither will a cup of coffee with a little butter. You have to let go of the almost religious fervor surrounding the "purity" of fasting.
What happens in your body when you fast
To understand why electrolytes are so critical, you need to understand what happens during intermittent fasting. When you stop eating for 12–18 hours (16:8 protocol) or more, your body activates real metabolic changes:
- Insulin lowers, allowing easier access to stored fat.
- Fat burning accelerates, especially if you maintain the fast long enough to reach light ketosis.
- Your brain works differently, using ketones as fuel. Many people report improved mental clarity.
- Your cells recycle themselves (autophagy), cleaning up damaged components.
All of this sounds good in theory. In practice, however, fasting has a diuretic effect: the body loses fluids and sodium faster than usual. Without replenishing them, fatigue, dizziness, cramps, headaches, and difficulty concentrating appear. But this is completely avoidable.
Does an electrolyte drink break a fast?
No, provided it meets two criteria:
- Less than 40–50 calories per serving: some clinical studies of modified fasting even set the limit at 100 kcal.
- Zero sugars or carbohydrates that stimulate insulin: no glucose, no fructose, no problematic sweeteners.
When caloric intake remains low and insulin does not rise, your body maintains the metabolic state of fasting. Ketosis continues. The benefits are preserved.
The difference lies in the ingredients:
- Sugar-free and low-calorie drinks (like LIT, with less than 8 kcal): do not break the fast.
- Sugared isotonic drinks (Aquarius, Electrolit, industrial juices): raise insulin and break the fast.
Complete guide: what you can drink during intermittent fasting
| Drink | Breaks fast? | Details |
|---|---|---|
| Plain water | No | Essential, but doesn't replenish lost minerals. |
| Black coffee | No | Provides antioxidants and can improve autophagy. |
| Tea (green, black, herbal) | No | No sugar, all are valid. Green tea adds extra antioxidants. |
| Sugar-free electrolyte water | No | The ideal option. Maintains mineral balance, prevents fatigue, and preserves ketosis. |
| Homemade broth or bone broth | Probably not* | Contains collagen and minerals, but also some protein. |
| Coffee with butter or MCT oil | Probably not | Low insulin impact, but be careful with calories. |
| Sodas or sugary isotonic drinks | Yes | Raise insulin and interrupt the fast. Avoid them. |
| "Sugar-free" drinks with artificial sweeteners | Varies | Aspartame and sucralose do not raise insulin, but may affect your microbiota. |
| Diet soda or zero soda | Better with stevia | Prefer versions sweetened with stevia or monk fruit. |
Why drinking only water during fasting is counterproductive
Many people believe that drinking more water is always better. But during fasting, that can be counterproductive. Fasting has a diuretic effect and increases the loss of fluids and electrolytes. If you only replenish water, you dilute the sodium in your blood, increasing the risk of hyponatremia (low sodium).
Symptoms include headache, fatigue, cramps, muscle weakness, dizziness, and, in severe cases, confusion or seizures.
The three electrolytes that really matter
- Sodium (300–500 mg): maintains fluid volume and blood pressure.
- Potassium (150–200 mg): regulates muscle and nerve function.
- Magnesium (60–100 mg): improves mental clarity, reduces anxiety, and facilitates sleep.
How to maintain balance during fasting
- Start your morning with a glass of electrolyte water.
- Drink according to your thirst, not by schedule.
- If you train fasted, increase electrolyte replenishment.
- Avoid sugary or high-calorie drinks.
- If you notice fatigue after several days, check your electrolytes first.
LIT: electrolyte drink designed for intermittent fasting
If you are looking for a practical solution, without having to mix salts and supplements, LIT is specifically formulated to maintain your energy without breaking the fast:
- 500 mg of sodium → compensates for losses.
- 150 mg of potassium → prevents cramps and maintains neurological function.
- 60 mg of magnesium → mental clarity without fatigue.
- Less than 8 kcal → no impact on fasting or ketosis.
- Zero sugar → zero insulin stimulation.
- Mild lemon flavor → combines perfectly with water.
Staying well-hydrated does not break intermittent fasting. It improves it. With the correct electrolytes, your experience changes completely: more energy, better mental clarity, and more sustainable fasts.
Scientific references
- Judelson, D. A., et al. (2007). Effect of hydration state on cognitive performance in collegiate athletes. International Journal of Sport Nutrition and Exercise Metabolism, 17(2), 172–185. Even mild dehydration (~2% body mass) affects cognitive and physical performance.
- Maughan, R. J., & Shirreffs, S. M. (2010). Development of hydration strategies to optimize performance for athletes in different environments. Journal of Sports Sciences, 28(s1), S1–S10. Explains how fluid and sodium loss reduces physical and mental capacity, and the importance of electrolyte balance.
- Casa, D. J., et al. (2000). National Athletic Trainers' Association Position Statement: Fluid Replacement for Athletes. Journal of Athletic Training, 35(2), 212–224. Key document establishing the principles of fluid and electrolyte replacement during exertion.
- Sawka, M. N., et al. (2007). American College of Sports Medicine position stand: Exercise and fluid replacement. Medicine & Science in Sports & Exercise, 39(2), 377–390. Reference study on the physiology of hydration, the role of sodium, and the prevention of hyponatremia.
- Ganio, M. S., et al. (2011). Mild dehydration impairs cognitive performance and mood of men. British Journal of Nutrition, 106(10), 1535–1543. Proves that even mild dehydration alters mood and concentration.
- O’Donnell, M. J., et al. (2011). Urinary sodium and potassium excretion and risk of cardiovascular events. JAMA, 306(20), 2229–2238. Describes the "U-shaped" relationship between sodium and health, supporting the idea of an optimal intake range.
- European Food Safety Authority (EFSA). (2019). Dietary Reference Values for sodium and potassium. EFSA Journal, 17(9), 5778. European reference values for daily sodium and potassium intake.
