Insulin resistance changes the fasting equation
With insulin resistance, your cells do not respond efficiently to insulin. Blood glucose stays elevated; fat stores stay locked. Dr. Boz describes patients who fast 48+ hours yet glucose remains in the hundreds — a sign the body is not yet burning fat effectively.
Research on prolonged fasting in severely obese patients showed glucose could stay elevated for days while ketones lagged — the body breaking down muscle instead of tapping fat. That is why "fast harder" is not always the answer.
The Dr. Boz approach: stabilize first
Dr. Boz recommends delaying prolonged fasts until metabolism improves. Start with a low-carb, adequate-fat eating pattern. Track the Dr. Boz Ratio (glucose ÷ ketones) — aim below 80, ideally below 40, before pushing 24-hour+ fasts.
Dr. Eric Westman adds patience: blood sugar normalization on keto can take months, not days. Intermittent 16:8 while keeping carbs low is often more sustainable than jumping to multi-day water fasts.
Signs you should not extend your fast
Stop or shorten your fast and eat a proper low-carb meal if you notice persistent weakness, shakiness, heart palpitations, or fasting glucose staying above ~120 mg/dL after 24+ hours without ketones rising.
If you take metformin, insulin, sulfonylureas, or blood pressure medication, fasting requires medical supervision — doses may need lowering to prevent dangerous lows.
A practical progression
- Weeks 1–4: Low-carb meals, track net carbs (50g or less for IR).
- Weeks 2–6: Natural 12–14 hour overnight fasts as hunger allows.
- Weeks 4–8: 16:8 IF if Dr. Boz Ratio and energy improve.
- Later: Occasional 24-hour gut resets — not weekly marathons until metrics support it.