Whether supplements "break" your fast depends on why you're fasting. Weight loss fasting has different rules than autophagy fasting.
What "Breaking a Fast" Actually Means
For weight loss (calorie restriction): A "broken" fast means consuming significant calories. Most supplements have negligible calories and won't affect results.
For insulin/metabolic fasting: Anything that spikes insulin could interfere. This mainly means carbs and protein, which most supplements don't contain.
For autophagy (cellular cleanup): This is strictest. Even small amounts of nutrients may reduce autophagy. We don't fully understand the thresholds yet.
For religious fasting: Rules vary. Check with your specific practice.
Safe During Most Fasts
Water-soluble vitamins: B vitamins, Vitamin C - no calories, no insulin response.
Minerals: Magnesium, zinc, potassium - especially important during extended fasts.
Electrolytes: Sodium, potassium, magnesium - crucial for longer fasts.
Black coffee and plain tea: Minimal calories, may enhance fat burning.
Apple cider vinegar: Negligible calories.
Creatine: No calories, doesn't spike insulin (though some prefer taking with food for absorption).
Better With Food
Fat-soluble vitamins (A, D, E, K): They need fat for absorption. Taking them fasted is mostly wasted. Wait until your eating window.
Fish oil / Omega-3s: Oil has calories (~40 per softgel) and needs fat for absorption. Take with meals.
CoQ10 (especially ubiquinone): Fat-soluble. Take with a fat-containing meal.
Curcumin/Turmeric: Much better absorbed with fat and black pepper. Wait for meals.
Protein powder: Definitely breaks a fast. 100+ calories and triggers insulin. Save for eating window.
The Practical Approach
If you're doing 16:8 intermittent fasting for weight loss: Most supplements are fine during the fast. Move fat-soluble ones to your eating window for better absorption.
If you're doing longer fasts (24-72+ hours): Electrolytes become important. Take magnesium, potassium, sodium. Skip most others.
If you're fasting specifically for autophagy: Be strict. Stick to water, electrolytes, and possibly black coffee/tea. Take other supplements during eating windows.
If in doubt: Take supplements with food. You'll absorb them better, and you won't have to worry about whether they "count."
The Bottom Line
For most intermittent fasters, supplements aren't a concern. Move fat-soluble vitamins to meals for absorption, keep electrolytes during the fast if needed, and don't stress about it.