Who Should Avoid Intermittent Fasting

Intermittent fasting has real benefits, but it is not appropriate for everyone. Some people should avoid it entirely, and everyone else should start gradually. Ignoring this advice can cause genuine harm.

Who Should Not Fast

Pregnant or nursing women. Growing a baby or producing breast milk requires consistent energy and nutrient availability. Fasting can reduce nutrient transfer and affect milk supply. This is not the time to experiment with meal timing [1].

People with a history of eating disorders. IF can reinforce harmful patterns around food restriction, perfectionism, and control. Research has raised concerns that fasting protocols may trigger or worsen disordered eating behaviours, particularly in individuals with a history of anorexia nervosa or bulimia [3]. If your relationship with food is complicated, talk to a professional before trying any fasting protocol.

People with type 1 diabetes. Type 1 diabetics rely on exogenous insulin and are at risk of dangerous hypoglycaemia during fasting periods. The clinical management of fasting in diabetes requires close medical supervision and is not something to self-prescribe from a blog post [2].

Underweight individuals. If your BMI is below 18.5 or you're already struggling to maintain weight, fasting will work against you. You need caloric surplus, not restriction.

Children and adolescents. Growing bodies need regular fuel. There is no evidence supporting IF for anyone under 18, and the risks — nutrient deficiency, growth impairment, disordered eating patterns — are real.