Fasting can suit lots of people, but it really isn't for everyone, and that's completely fine. Skipping it is a perfectly good choice. Here's who should steer clear, or have a chat with a doctor first.
It's usually best to skip fasting if you're under 18, because growing bodies need regular fuel. The same goes if you're pregnant or breastfeeding. If you have a history of eating disorders, fasting can bring old patterns back, so please skip it and look after yourself first.
Please talk to a doctor before starting if you have diabetes or take anything that affects your blood sugar, like insulin. Missing meals can change how those medicines work. The same goes for other medication or health conditions. A quick chat can help you work out whether fasting is safe for you, and how to adjust things if it is.
Whoever you are, treat your body as the boss. Stop the fast and eat something if you feel faint, dizzy, unwell or confused, or if your heart is racing. Those aren't signs you need to push through. They're signs it's time for a snack, a sit-down and a drink of water.
Ending a fast early isn't failing. It's you listening, which is the whole point. In Step Step you can jot down how you felt in the notes, which makes a handy record to share with your doctor.
Who should not do intermittent fasting?
Skipping fasting is the safer choice if you are under 18, pregnant, trying to conceive, or breastfeeding. Growing bodies and babies need steady energy and nutrients, and fasting is not a good fit for these stages.
It is also best avoided if you have, or have ever had, an eating disorder such as anorexia, bulimia or binge eating disorder. Rules about when you may eat can bring old patterns back. If you think fasting is starting to feel like a rule you have to obey or a way to punish yourself, stop and talk to someone you trust or a doctor.
People who are underweight, recovering from illness or surgery, or who are frail or older with a poor appetite should also get advice first.
If you are unsure whether you fall into any of these groups, ask. A GP, practice nurse or pharmacist will not think it a silly question, and a no today does not mean a no forever.
Which medical conditions need a doctor's advice before fasting?
Diabetes is the main one. Insulin and some tablets can push blood sugar too low if you skip meals. The dose or timing may need to change, and only your doctor or diabetes nurse can say how.
Check with a doctor too if you take regular medication, especially for blood pressure, heart conditions, kidney problems or anything that must be taken with food. Some medicines upset the stomach when taken empty, and some affect hydration. Others have a risk of low blood pressure or low blood sugar when you eat less.
Gallstones, a history of gout, low blood pressure, and reflux can also be affected. A short appointment now is better than a problem later. Take a note of what you plan to try, such as a 14 hour overnight break, so the advice can be specific.
What are the warning signs to stop a fast?
Stop and eat if you feel faint, dizzy, shaky, sick or confused. The same goes for a racing or irregular heartbeat, chest pain, severe headache, or fainting. None of these is a sign to push through.
Drink water, sit down and eat something with some carbohydrate and protein, such as toast with eggs or a banana with yoghurt. If symptoms do not settle within a short time, or you feel very unwell, get medical help.
Ending a fast early is not failing. It is a sensible response to what your body is telling you.
Do not fast when you are ill with a fever, vomiting or diarrhoea. Your body needs fluids and food to recover, and you can pick it up again when you feel well.
What are gentler alternatives to fasting?
If fasting is not for you, you can still get structure around your day. Eat regular meals. Try finishing the evening meal a little earlier and having a proper breakfast. Move after meals, for example a short walk, and keep an eye on sleep and water.
Many of the habits people like about fasting, such as less mindless snacking and a calmer routine, can be built without long gaps between meals. The Step Goal Planner on this site can help you set a daily walking target if gentle movement appeals more.
If you want to talk through what would suit you, a registered dietitian can help you build a pattern around your health, medication and routine. In the UK, your GP can refer you, and the NHS website has a clear section on healthy eating and weight.
Common questions
Who should avoid intermittent fasting?
Anyone under 18, pregnant or breastfeeding, or with a history of an eating disorder should avoid it. People with diabetes or on regular medication need a doctor's advice first.
Is fasting safe for people with diabetes?
Not without medical guidance. Skipping meals can cause low blood sugar, especially with insulin or certain tablets. Talk to your doctor or diabetes team before trying it.
Can I fast if I take medication?
It depends on the medicine. Some must be taken with food, and some affect blood pressure or blood sugar. Ask your doctor or pharmacist before you change when you eat.
When should I stop a fast?
Stop and eat if you feel faint, dizzy, shaky, unwell, confused or have a racing heart. If symptoms persist after eating and drinking, seek medical advice.
Updated October 25, 2026
This is general information, not medical advice. Check with your doctor before you start fasting, especially if you have a health condition, are pregnant or take medication.
