When not to fast: the honest list

Why this page is direct rather than gentle

Most of the fasting pages on this site are written to help people make gradual, well-informed choices. This one is different on purpose. Some situations aren't a matter of finding the right pace or the right window — they're situations where fasting simply isn't the right tool, and dressing that up in soft language does a disservice to anyone reading in good faith. So this list is stated plainly rather than hedged.

Pregnancy, breastfeeding and adolescence

If you are pregnant or breastfeeding, do not fast. Nutritional needs during pregnancy and while breastfeeding are higher and more consistent than fasting allows for, and this is not a case where a gentle 12:12 window is a safe compromise — speak to your doctor or midwife about nutrition instead of adapting a fasting plan to this period of life. The same applies, for different reasons, to adolescents: growing bodies have different nutritional needs from adult bodies, and intermittent fasting is not appropriate for teenagers.

Diabetes and blood-pressure medication

If you have type 1 diabetes, do not fast without your medical team directly involved in planning it — insulin dosing and fasting interact in ways that carry a real risk of dangerously low blood sugar, and this needs individual clinical management, not general advice from an article. If you have type 2 diabetes and take medication for it, particularly insulin or sulfonylureas, the same applies: talk to your doctor before making any change to eating timing, since medication doses may need adjusting alongside it. If you take blood-pressure medication, fasting can affect how your blood pressure responds, especially in the early days of a longer fasting window, and this too warrants a conversation with your doctor first, not just careful self-monitoring.

Underweight or losing weight unintentionally

If you are underweight, or have been losing weight without meaning to, fasting is not appropriate. This site does not frame intermittent fasting as a weight-loss tool in any case, but it's worth being explicit here: adding a fasting pattern on top of unintentional weight loss or an already low body weight adds risk without any offsetting benefit, and the right next step is a conversation with a doctor about the underlying cause of the weight change.

Any history of an eating disorder

If you have any history of an eating disorder — whether recent or years in the past, whether formally diagnosed or not — intermittent fasting is not appropriate for you. This is not a matter of degree or of "being careful." Structured rules about when and whether to eat can interact badly with a history of disordered eating regardless of how long ago it was or how recovered you feel, and this site does not recommend fasting as something to attempt alongside or in spite of that history. If you're unsure whether this applies to you, treat the uncertainty itself as a reason to speak with a doctor or a mental health professional before considering fasting, rather than deciding on your own.

Kidney and heart conditions, and recovery from illness or surgery

Certain kidney conditions affect how the body manages fluid and electrolyte balance, which fasting can complicate; if you have any diagnosed kidney condition, this needs to be a conversation with your specialist, not a decision made from a general guide. Similarly, certain heart conditions — particularly anything involving arrhythmia or heart failure — mean fasting-related shifts in blood pressure and electrolyte balance carry more weight than they would for someone without a cardiac history, and again, this calls for your cardiologist's input specifically. If you are recovering from any recent illness, infection or surgery, your body's nutritional needs during recovery are higher, not lower, and this is not the time to introduce a new restriction on eating, regardless of how mild it seems.

Heavy physical work and specific practice contexts

If your day involves genuinely heavy physical labour, a narrow eating window can leave you under-fuelled for the demands of the work, with real risk of fatigue-related accidents; this is worth weighing honestly rather than assuming any fasting schedule fits any lifestyle. On the practice side, long breath-retention work (extended kumbhaka) and strongly heating pranayama practices such as vigorous bhastrika are best not combined with an extended fast, particularly in its early days — the physiological load of a demanding breath practice and the physiological load of fasting can compound in ways that are uncomfortable at best and genuinely destabilising at worst. If you keep this kind of practice, read pranayama alongside this page and consider keeping any fasting window modest, or practising such techniques within your eating window rather than deep into a fast. General guidance on sequencing food and practice is also covered in fasting before yoga and breaking a fast after practice.

Stop today: symptoms that apply to anyone

Regardless of experience level or how carefully you've planned a fast, stop eating according to the fasting schedule and eat something today if you notice any of the following: fainting or near-fainting, a racing or irregular heartbeat, marked confusion or difficulty thinking clearly, severe or worsening headache, shaking that doesn't settle with rest, or any sense that something is genuinely wrong rather than merely uncomfortable. These are not symptoms to push through as part of "getting used to it." If any of them recur once you've resumed normal eating, or if you're at all unsure, contact a doctor.

The plain summary

Fasting is an optional, low-stakes experiment for a healthy adult with none of the conditions above, approached gradually and reviewed honestly, as covered in intermittent fasting for beginners. It is not a universal practice, and there is no obligation, spiritual or otherwise, to make it work for you if your situation is on this list. Choosing not to fast, in any of these circumstances, is the correct choice, not a failure of discipline.