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Should you fast? A two-minute check

A few quick questions about your health and your plans. You’ll find out whether a 3 to 10 day water fast is ruled out for you, needs your GP first, or isn’t ruled out by anything here.

How it works

Answer each question, then press See my result. You’ll get one of three answers:

  • Red Don’t fast. We’ll say why in plain words, and what to do instead.
  • Amber Talk to your GP first. You’ll get a letter to take to the appointment.
  • Green Nothing here rules it out. You’ll still need the stop rules and the full list of who should not fast.

Nothing you answer is kept. Your answers are used once, to work out your result, and then thrown away. They never appear in the page address. All we keep is a daily count of how many results were red, amber or green.

This is a screening aid, not medical advice, and it can’t replace a doctor who knows you. Feeling unwell during a fast? Stop, and call 999 in an emergency or NHS 111 if it’s urgent but not life-threatening.

About you

How old are you?
Are you pregnant, breastfeeding or trying for a baby?
Are you underweight, or have you lost weight recently without trying?

Underweight means a BMI under 18.5. Losing weight without trying means you weren't dieting: for example, more than a tenth of your weight in the last 3 to 6 months. If a doctor has told you that you are underweight or malnourished, answer Yes.

Not sure? Work out your BMI

Use centimetres or feet and inches, and kilograms or stones and pounds. Your height and weight are used once, to work out your BMI, and are not kept.

Heightor
Weightor

Are you frail?

For example, everyday tasks wear you out, you walk slowly or need help to get about, or you have had falls.

Have you ever had an eating disorder, or a difficult relationship with food?

Such as anorexia, bulimia or binge eating disorder, now or in the past, whether or not it was ever diagnosed.

Your health

Do you have diabetes?
Do you have a heart condition, or have you had one in the past?

Such as heart disease, angina, a heart attack, heart failure, or an irregular heartbeat (arrhythmia) like atrial fibrillation.

Do you have kidney or liver disease, or have you ever had kidney stones?

Such as chronic kidney disease, cirrhosis or hepatitis.

Do you have Addison's disease, or an overactive thyroid that isn't under control yet?

Addison's disease is also called adrenal insufficiency. An overactive thyroid is also called hyperthyroidism.

Do you have gout?
Has a blood test ever shown low potassium, magnesium or phosphate?

Answer Yes even if it was put right afterwards.

Your medicines

Do you take insulin, or a sulfonylurea such as gliclazide?

Other sulfonylureas are glimepiride, glibenclamide and tolbutamide. Repaglinide works in a similar way, so answer Yes for that too.

Do you take any medicine that has to be taken with food?

The label or leaflet will say ‘take with or after food’. Also answer Yes if you take warfarin, an immunosuppressant, or an anti-inflammatory painkiller such as ibuprofen or naproxen regularly: our list of who should not fast puts these in the same group. Some antipsychotics and antidepressants need food too, so check the leaflet. Not sure? Your pharmacist can tell you.

Do you take tablets for blood pressure, water tablets (diuretics) or lithium?

Blood pressure tablets include ACE inhibitors (names ending in -pril, such as ramipril) and ARBs (names ending in -sartan, such as losartan).

Right now

Have you been ill or had an infection in the last month, or had an operation in the last three months?
Are you being treated for a mental health condition?

Such as depression, anxiety or bipolar disorder, with medicine or talking therapy.

Do you usually drink more than 14 units of alcohol a week, or have you ever been dependent on alcohol?

14 units is about 6 pints of average-strength beer or 10 small glasses of lower-strength wine.

Your plan

This doesn't change your result. It goes in your GP letter, and it changes what we point you to.

Would this be your first fast longer than 72 hours?

This doesn't change your result either.

Your answers are used once, to work out your result, and are not kept.

Read next

Questions

Does this check keep my answers?

No. Your answers are sent once, to work out your result, and then thrown away: they are not saved, logged or put in the page address. The only record is an anonymous daily tally of how many results were red, amber or green, and you are left out of even that if you have switched off counting on the Your data page, or your browser sends Do Not Track or Global Privacy Control.

Is a green result a medical all-clear?

No. It means none of your answers ruled a fast out. The check asks about the most common reasons not to fast, not every one, and it cannot know your medical history. The protocol still asks for medical clearance before a long fast, and the full list of who should not fast is worth reading first.

Why does it ask about my medicines?

Some medicines lower blood sugar whether or not you eat, some harm the stomach when it is empty, and some change how your body handles salt and water. A fast can turn a normal dose into a risky one, so your GP needs to plan each medicine with you before you start.

How we count visits, and how to switch it off: your data and choices.