Net carbs are total carbohydrates minus fiber and often sugar alcohols. Keto and low-carb diets use them to track daily carb intake.

Is this medical advice?

No. These calculators provide estimates for education only. Work with your healthcare provider — especially if you have diabetes, take insulin, or manage blood pressure medications.

How long should I fast?

Dr. Mindy Pelz starts most people at 13–16 hours. Autophagy benefits increase around 17 hours. Extended 24–72 hour fasts need medical awareness — especially on medications.

Which calculator should I use first?

Use the net carb calculator when reading a food label. Use the macro calculator for daily targets. Use the fasting clock when you are ready to track fasts after low-carb eating feels stable.

Fasting · 8 min read

Fasting on Diabetes and Blood Pressure Medications — Safety Basics

Why insulin, sulfonylureas, and BP meds require doctor supervision before extended fasts.

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Why medications matter

Dr. Eric Westman warns that fasting while on insulin or sulfonylureas can cause dangerous hypoglycemia. Blood pressure medications may need adjustment as weight and sodium intake change during fasts.

Never stop or reduce prescriptions without your prescriber. Many clinics use supervised low-carb programs with medication tapering plans.

Safer progression

Stabilize low-carb eating for weeks before extended fasts (Dr. Boz)
Start with 13–16 hour windows; monitor glucose if your doctor recommends
Use assisted fasting with sodium for 24h+ only with clearance
Break fasts immediately if shaky, confused, or severely hypoglycemic

Frequently asked questions

Can I fast on metformin?

Metformin is lower hypoglycemia risk than insulin secretagogues, but still discuss fasting plans with your prescriber — especially beyond 24 hours.

Insulin resistance

Fasting With Insulin Resistance — When to Go Slow

Why extended fasting can fail with insulin resistance. Dr. Boz on glucose, ketones, and building metabolic readiness before long fasts.

9 min read

Fasting

Water Fast vs Assisted Fast — Electrolytes Explained

Strict water-only fasting vs assisted fasting with salt, bouillon, and electrolytes. Guidance from Dr. Westman and Dr. Boz for safe extended fasts.

6 min read

Metabolic Low Carb Calculator provides educational content only — not medical advice, diagnosis, or treatment. Talk to your healthcare provider before changing diet, fasting, or medications. Read disclaimer