When does a ‘healthy diet’ become unhealthy? This week the Food Chain looks at Orthorexia Nervosa - an unofficial term used to describe an eating disorder where people restrict their diet based on the quality and purity of food, rather than its quantity. The BBC’s Emily Thomas talks to women who have suffered from following extreme healthy diets, and hears how their internet use influenced their eating behaviour. We also hear from the people trying to help those whose quality of life is being destroyed in their pursuit of quality food.

If you or someone you know has been affected by eating disorders please see the links to resources at the bottom of this page.

Photo: Woman rejecting water and lettuce Credit: Getty Images