Does water break a fast?

No. Plain water has zero calories and does not affect insulin or autophagy. Drink freely during your fasting window.

Does sparkling water break a fast?

No. Plain sparkling water (no flavouring, no sweeteners) is the same as still water — it does not break your fast.

Does gum break a fast?

For a caloric fast, sugar-free gum is generally safe (~2 calories per piece). However, the act of chewing may stimulate digestive enzymes. For strict fasting goals, avoid it.

Do electrolytes break a fast?

Zero-calorie electrolyte powders or salt water do not break a caloric fast. Avoid electrolytes with added sugar or BCAAs.

Does apple cider vinegar break a fast?

ACV has ~3 calories per tablespoon — trace amounts. It does not meaningfully break a caloric or insulin fast. Some use it to aid digestion during fasting.

What Breaks a Fast? The Definitive Guide (2026)

What breaks a fast depends entirely on your fasting goal. There are three main frameworks people use:

Strict caloric fast — anything with calories breaks it
Insulin-focused fast — anything that raises insulin breaks it
Autophagy-focused fast — protein (especially) suppresses autophagy signalling

Complete Reference Table

Item	Caloric Fast	Insulin Fast	Autophagy Fast
Water (still)	✅ Safe	✅ Safe	✅ Safe
Sparkling water	✅ Safe	✅ Safe	✅ Safe
Black coffee	✅ Safe	✅ Safe	✅ Safe
Plain black tea	✅ Safe	✅ Safe	✅ Safe
Herbal tea (unsweetened)	✅ Safe	✅ Safe	✅ Safe
Salt / electrolytes (0 cal)	✅ Safe	✅ Safe	✅ Safe
Apple cider vinegar	✅ Trace	✅ Safe	✅ Safe
Sugar-free gum	✅ Safe	⚠️ Maybe	✅ Safe
Milk / cream	❌ Breaks	❌ Breaks	❌ Breaks
Sugar	❌ Breaks	❌ Breaks	❌ Breaks
Artificial sweeteners	✅ 0 cal	⚠️ Maybe	⚠️ Maybe
BCAA supplements	⚠️ Trace	❌ Breaks	❌ Breaks
Collagen / protein powder	❌ Breaks	❌ Breaks	❌ Breaks
MCT oil	❌ Breaks	⚠️ Minimal	⚠️ Minimal
Bone broth	❌ Breaks	❌ Breaks	❌ Breaks
Vitamins / supplements (no cal)	✅ Safe	✅ Safe	✅ Safe
Medications	✅ Safe*	✅ Safe*	✅ Safe*

* Always follow your doctor's instructions for medication timing.

The Grey Areas Explained

Artificial Sweeteners

Some studies suggest certain artificial sweeteners (saccharin, sucralose) may trigger a cephalic insulin response — a small insulin spike from taste alone. Evidence is mixed. For a strict insulin or autophagy fast, avoid sweeteners entirely.

BCAA Supplements

Branched-chain amino acids stimulate mTOR and suppress autophagy — even in small doses. If autophagy is your goal, skip BCAAs entirely during your fasting window.

MCT Oil

MCT oil contains 100 calories per tablespoon and technically breaks a caloric fast. However, it is ketogenic and does not significantly raise insulin — making it compatible with some ketosis-focused fasting approaches.

The Simple Rules to Remember

🟢 Always OK: Water, black coffee, plain tea, salt
🟡 Use caution: Sugar-free gum, artificial sweeteners, ACV
🔴 Always breaks fast: Anything with protein, carbs, or significant fat