Intermittent fasting means leaving longer gaps between meals, for example eating only inside an 8-hour window. For many healthy adults a gentle version is a harmless experiment. But it is not for everyone, and the people it suits least are often the ones who most want a simple rule to follow. This guide is a quick check you can do before you try any fasting pattern.
Health services in the UK are fairly consistent on this. The NHS London guidance says people with a history of eating disorders such as anorexia or bulimia, and women who are pregnant or breastfeeding, should not attempt intermittent fasting. The British Heart Foundation adds people who have diabetes or low blood sugar, who are underweight, or who are children or teenagers. The British Dietetic Association advises never to delay or skip meals if you have diabetes.
The reasons are practical. Growing bodies, pregnancy and breastfeeding raise your need for energy and nutrients. Diabetes medicines can push blood sugar too low if meals are delayed. And any plan built on rules about when you may eat can feed an unhealthy relationship with food in someone who has struggled with one.
If you take regular medicines, especially for diabetes or blood pressure, change when you eat only after talking to your GP, pharmacist or practice nurse. Some tablets need to be taken with food, and some doses may need adjusting when your eating pattern changes. The same goes for any long-term health condition you are unsure about.
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Does any of this apply to you?
If you can tick any of the first five boxes, regular meals are the safer plan.
Even if you are in the clear, fasting can still go wrong. Stop and eat if you feel faint, shaky, confused or very weak. Be honest with yourself about your thoughts too. If you find yourself dreading meals, feeling guilty after eating, or thinking about food all day, the pattern is costing more than it gives. It is a tool, not a test of willpower.
The evidence is mixed. Fasting patterns can help some people eat less overall, which can lead to weight loss, but studies generally find results similar to other ways of reducing calories, and long-term data is limited. Nobody has to fast to be healthy. Eating a balanced diet with regular meals suits most people just as well.
This is general information, not medical advice. If you have a condition, are pregnant or breastfeeding, have or had an eating disorder, or take medication, talk to a doctor first.