Water-only fasting
Plain water only — no calories, no broth, no supplements with calories. Strictest form, often used for shorter fasts (16–24 hours) or by experienced fasters.
Risk: electrolyte loss. Dr. Eric Westman stresses that low-carb diets and fasting both increase sodium needs. Headaches, dizziness, and muscle cramps on water-only fasts often mean you need salt, not more willpower.
Assisted fasting — what is allowed
Assisted fasting adds non-caloric support: water, plain salt or electrolyte mixes without sugar, bouillon/bone broth (Dr. Westman recommends a cup daily for sodium), black coffee, and plain tea.
Dr. Boz is direct: "Salt + water are best" during fasts. This is not cheating — it prevents preventable side effects and helps you complete the fast safely.
Which should you choose?
For 16–18 hour IF: water alone may be fine if you salt food well when you eat. For 24 hours and beyond: assisted fasting is strongly recommended.
Our fasting clock lets you toggle modes and shows tailored hydration tips as your timer runs.
- 16–18h IF, feel good → water or assisted both work
- 24h+ gut reset → assisted with bouillon
- 36–72h extended → assisted only for most people
- History of kidney issues → ask your doctor before high sodium