What you drink during a fast matters more than most beginners think. The goal for a standard intermittent fast is to avoid calories and significant insulin spikes so your body stays in a fasted state. Here is a practical breakdown.
Always fine (for most IF protocols)
- Water — still or sparkling, unflavored
- Black coffee — no sugar, no milk, no cream
- Plain tea — green, black, herbal without added sugar or juice
These are the safest defaults. When starting out, keep it boring.
Usually fine, with nuance
- Zero-calorie electrolyte tabs/powders — check labels; avoid sugar and maltodextrin.
- Artificial sweeteners — unlikely to break a strict fast technically, but may increase cravings for some people.
- Apple cider vinegar — tiny amounts in water; negligible calories.
- Lemon in water — a squeeze is minimal; heavy juice is not.
Breaks a fast (avoid during the window)
- Milk, cream, butter coffee (“bulletproof”), coconut oil
- Protein shakes, BCAAs, collagen with calories
- Bone broth with fat or significant protein
- Juice, soda, alcohol, sweetened coffee drinks
- Most “meal replacement” or “fasting” branded drinks with calories
Does diet soda break a fast?
Technically, zero-calorie diet soda does not add calories. Practically, it may trigger appetite or gut discomfort in some people. If it helps you finish a fast without derailing later meals, occasional use is a personal choice—not a health food.
Coffee tips that actually help
- Drink water first; coffee is not hydration.
- Cap caffeine if sleep suffers—especially with afternoon fasting.
- If black coffee is unbearable, shorten the fast or shift the window instead of adding cream daily.
Hydration during longer fasts
For 16–18 hour daily fasts, water plus normal meals usually cover hydration. If you feel lightheaded, add electrolytes (sodium, potassium, magnesium) without sugar—especially in hot weather or if you sweat heavily.