Is intermittent fasting right for you?
Who should get individual medical advice first, why medicines matter, and the signs that mean you should stop.
Talk with a healthcare professional before changing how you eat if you have a medical condition, take medication, are pregnant or breastfeeding, are under 18, or have a history of disordered eating. Stop and seek help if you feel unwell.
Fasting is not for everyone
Changing when you eat can affect blood sugar, hydration, medicines and mood. For many healthy adults a moderate eating window is low risk, but for some people it can be harmful. Johns Hopkins Medicine advises talking to your doctor before you start and lists groups who should not try intermittent fasting.
Who should not try it without medical advice
- Children and teens under 18. Growing bodies need regular nourishment.
- People who are pregnant or breastfeeding.
- People with type 1 diabetes who take insulin. Johns Hopkins lists this group, and the NIDDK notes that people with type 1 diabetes are at greater risk when fasting than people with type 2.
- Anyone with a history of eating disorders. Structured fasting can trigger restrictive patterns. If this applies to you, please talk with your care team rather than using fasting tools.
Talk to a clinician first if you
- take medicines for diabetes, especially insulin, sulfonylureas or other drugs that can cause low blood sugar
- take medicines that must be taken with food, or diuretics (water pills)
- have heart, kidney or liver disease, low blood pressure, or have recently been unwell
- are older, frail or have had unintended weight loss
- have a health condition you are not sure about
The NIDDK explains that low blood sugar (hypoglycemia) is the main risk when people with diabetes fast, and that medicines often need adjusting under medical supervision. Never change the dose or timing of a medicine based on a calculator or website.
Signs to stop
Stop fasting and eat if you feel faint, dizzy, shaky, confused, very weak, have a racing heartbeat, or feel unwell in any way that worries you. Johns Hopkins advises talking to your doctor if you experience unusual anxiety, headaches, nausea or other symptoms after starting. Seek urgent medical help for severe symptoms.
A healthy relationship with food
Fasting should not become a source of guilt, anxiety or punishment. If you find yourself thinking about food constantly, feeling distressed when you eat outside a window, or using fasting to make up for eating, it may be time to step back and talk to a doctor. The tools on this site deliberately avoid streaks, scores and targets for this reason.
Medical fasting is different
If you have been told to fast before a blood test, surgery or a scan, follow your clinic’s instructions, including what you may drink and which medicines to take. Those instructions take priority over any routine.
Reviewed October 2026 by Lee Palmer · How we write our guides · Report an error