Medical disclaimer

Fasting Index publishes general information about fasting. It is not medical advice, it is not a substitute for talking to a doctor, and it is not written or reviewed by a clinician.

Who should not fast

Fasting is not safe for everyone, and for some people it is specifically dangerous. Do not fast, or speak to a doctor before you do, if any of the following apply to you:

• —You are pregnant or breastfeeding.
• —You are under 18.
• —You have a history of an eating disorder, or fasting feels like a way to restrict rather than a way to eat differently.
• —You have type 1 diabetes, or type 2 diabetes managed with insulin or sulfonylureas — fasting on these medications can cause dangerous hypoglycaemia, and the dose usually has to change before the fast does.
• —You take medication that must be taken with food.
• —You are underweight, or recovering from illness, surgery or injury.
• —You have kidney disease, liver disease, heart failure, or a condition affecting blood pressure or electrolytes.
• —You are on diuretics, lithium, or any drug with a narrow therapeutic window.

Stop fasting and seek medical help if

These are not reasons to push through. Ending a fast early costs you nothing that matters.

• —You feel faint, confused, or unusually weak.
• —Your heart is racing or beating irregularly.
• —You have chest pain, or shortness of breath at rest.
• —You are vomiting, or cannot keep water down.
• —You have symptoms of low blood sugar — shaking, sweating, confusion — particularly if you take diabetes medication.
• —You have not passed urine for many hours, or your urine is very dark.

Medical fasts are your clinic’s decision, not ours

Where a question is medical — fasting before blood work, before surgery, or before a scan — the instruction from the clinic or the anaesthetic team overrides anything on this site, including where we disagree with it. Preoperative fasting rules in particular exist to prevent aspiration during anaesthesia, and they are not a nutrition question. The blood-work verdict on every entry is written to send you to your clinic, not to replace it.

Never stop a prescribed medication to protect a fast

This is the single most important line on this page. If a medication must be taken with food, the food is not optional and the fast is the thing that gives way. If you want to change how a medication fits around a fast, that is a conversation with the prescriber, and it is often a straightforward one.

What we will never do

Fasting Index does not sell supplements and takes no affiliate revenue from any product it assesses. It makes no claim that fasting treats, cures or prevents any disease, and it publishes no testimonials of that kind. If you find a claim on this site that reads as a cure claim, that is an error — please report it and it will be corrected publicly.

If you are in a medical emergency, contact your local emergency number. This site cannot help you.