Who Should Not Fast
Contraindications · 6 min read
Fasting is a powerful tool, but it’s not for everyone. Certain medical conditions, life stages, and psychological factors make fasting inappropriate or potentially dangerous. Here’s who should avoid it.
Key Takeaways
- Pregnant and breastfeeding women should not fast.
- People with a history of eating disorders should approach fasting with extreme caution.
- Type 1 diabetics and those on insulin need medical supervision for any fasting.
- Underweight individuals (BMI < 18.5) should not pursue caloric restriction.
- Children and adolescents should not practice intermittent fasting.
Pregnancy & Breastfeeding
Pregnant and breastfeeding women need consistent caloric and nutrient intake to support fetal development and milk production. Fasting during pregnancy may restrict nutrient delivery to the developing baby. During breastfeeding, caloric restriction can reduce milk supply and quality. This is not the time for fasting — prioritize adequate nutrition with frequent, nutrient-dense meals.
Eating Disorder History
If you have a current or past eating disorder — anorexia, bulimia, binge eating disorder, or orthorexia — fasting can be a dangerous trigger. The restrictive nature of fasting can reinforce unhealthy patterns of control around food, amplify disordered eating behaviors, and disguise restriction as a ‘health practice.’ If you have a complicated relationship with food, work with a therapist or registered dietitian before considering any fasting protocol.
Type 1 Diabetes
People with type 1 diabetes lack the ability to produce insulin and rely on exogenous insulin to regulate blood sugar. Fasting without careful insulin management can cause dangerous hypoglycemia (low blood sugar) or diabetic ketoacidosis (DKA). If you have type 1 diabetes and want to explore fasting, it must be done under close medical supervision with continuous glucose monitoring.
Type 2 Diabetes on Medication
While fasting can improve insulin sensitivity — potentially beneficial for type 2 diabetes — it becomes complicated when combined with diabetes medications, especially sulfonylureas and insulin. These medications are dosed based on consistent food intake. Fasting without adjusting medication can cause dangerous hypoglycemia. Always consult your doctor and consider medication adjustments before starting any fasting protocol.
Underweight Individuals
If your BMI is below 18.5 or you’re already in a significant caloric deficit, fasting is contraindicated. You don’t have the energy reserves to safely support extended periods without food. Fasting in an underweight state can further deplete nutrient stores, worsen hormonal imbalances (low thyroid, low sex hormones), and compromise immune function.
Children & Adolescents
Growing bodies need consistent nutrition. Children and teenagers require regular caloric intake for bone development, brain maturation, hormonal development, and growth. Intermittent fasting should not be imposed on or recommended for anyone under 18. If an adolescent has weight concerns, focus on food quality and activity rather than restriction.
Other Conditions Requiring Caution
These conditions don’t necessarily prohibit fasting but require medical guidance:
- Chronic kidney disease — fasting affects electrolyte balance and kidney workload
- Gout — fasting can temporarily increase uric acid levels, triggering flares
- Gallstones — extended fasting may increase gallbladder issues in susceptible individuals
- Chronic high stress or adrenal fatigue — fasting adds a hormetic stressor
- Active infections or recovery from surgery — your body needs fuel to heal
- Amenorrhea or low hormone levels — fasting can worsen hormonal disruption in women
When to Stop Fasting
Even if you’re generally healthy, stop fasting and reassess if you experience persistent dizziness or fainting, inability to concentrate, heart palpitations, extreme irritability or mood changes, hair loss, menstrual irregularities, or if fasting is negatively affecting your relationships or quality of life. Fasting should feel sustainable and beneficial — not punishing.
The Bottom Line
Fasting is powerful but not universal. Pregnant women, those with eating disorder history, type 1 diabetics, underweight individuals, and children should avoid it. When in doubt, consult a healthcare provider before starting.