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Who should talk to a doctor before intermittent fasting

Intermittent fasting is widely discussed, and it is easy to forget that it does not suit everyone. This page lists the situations that public health sources single out. It does not replace a conversation with your doctor.

Situations named by public health sources

The Nutrition Source of the Harvard T.H. Chan School of Public Health lists conditions in which people should abstain from intermittent fasting:

  • diabetes;
  • eating disorders that involve unhealthy self-restriction, such as anorexia or bulimia nervosa;
  • use of medications that require food intake;
  • an active growth stage, such as adolescence;
  • pregnancy and breastfeeding.

If one of these applies to you, do not start fasting on your own. Talk to your doctor.

Other reasons to ask first

The same source notes that long periods without food can lead to overeating when food is reintroduced, and may encourage an increased fixation on food. If your relationship with food has been difficult in the past, raise it with a professional before you try any fasting schedule.

It is also sensible to ask first if you live with a chronic condition, take regular medication, are older, or are recovering from illness or surgery.

What the evidence says, briefly

Research in people is still young. The US National Institute on Aging writes that there is not enough evidence to recommend any calorie restriction or fasting regimen to the public, and that scientists do not yet know whether these eating patterns are safe in the long run.

That is a reason for modesty. An app, a book or a guide like this one cannot tell you whether fasting is right for you.

Questions to bring to your appointment

  • Is a daily eating window appropriate given my health and my medication?
  • Should any of my medication be taken with food, and at what time?
  • Which signs should make me stop?
  • Is there a length of fast I should not exceed?

If you feel unwell

Stop the fast and eat. Seek medical help if the symptoms are severe or do not pass. Ending a fast early is an ordinary decision, not a failure.

If fasting becomes a source of distress

If you find yourself anxious about eating, or pushing fasts longer to make up for meals, talk to a doctor or contact an eating disorder helpline in your country.

Related: what the plan numbers mean and what to check in a fasting app.

Sources

This guide is general information, not medical advice. Talk to a doctor before you start fasting.