Fasting Guides / Safety & Medical
Who Should Not Fast (Or Proceed With Caution)
An honest list of medical conditions and circumstances where fasting carries real risks — and what to do instead.
Clear Contraindications
Fasting is not appropriate for everyone. People who should not fast without direct medical supervision include: those with type 1 diabetes (insulin-dependent), anyone with a history of eating disorders (anorexia, bulimia, ARFID, or orthorexia), pregnant or breastfeeding women, children and adolescents under 18, people who are underweight (BMI under 18.5), and those recovering from major surgery or significant illness.
Type 2 Diabetes and Medication
People with type 2 diabetes can often benefit significantly from intermittent fasting, but medication management is critical. Sulfonylureas (glipizide, glimepiride) and insulin cause hypoglycemia — dangerously low blood sugar — in a fasted state. If you are on these medications and want to fast, work with your prescribing physician to adjust dosing. Metformin is generally safer with IF, but still warrants medical oversight.
Other Medications to Consider
Some medications must be taken with food to prevent stomach irritation (NSAIDs, certain antibiotics). Others have pharmacokinetics that are affected by fasting (some psychiatric medications, anticoagulants). If you take daily medications, review whether they need food with a pharmacist or physician before starting fasting.
Pregnancy and Breastfeeding
There is insufficient evidence on the safety of IF during pregnancy, and the caloric and nutritional needs during pregnancy and lactation are significantly increased. This is not the time for food restriction. Prioritizing nutrition, not restriction, is appropriate. These are phases of life to set fasting aside entirely.
Eating Disorder History
This is perhaps the most important caution in this entire knowledge base. Intermittent fasting, for someone with a history of restrictive eating disorders, can function as a relapse trigger or a vehicle for restriction rationalized as health optimization. If you have a history of disordered eating, consult a therapist or dietitian specializing in eating disorders before trying IF.