A quick internet search, a few clicks, and the screen flashes up an image of a young woman, tall, fully made-up - and frighteningly emaciated. Around me I hear a sharp intake of breath. I was filming a recent episode of the Channel 4 documentary Supersize vs Superskinny, in which we asked a group of parents to look at "thinspiration" websites - so called because they are dedicated to encouraging young women with eating disorders to maintain their life-threatening lifestyles.Such pro-anorexia and pro-bulimia sites give tips on how to avoid food. They suggest posting online "inspirational" images of your ribcage. They offer advice on how to hide your eating disorder from your family, even on how to "purge" silently.Little wonder, then, that the number of teenagers being admitted to hospital with eating disorders in the UK has nearly doubled in just three years. The Royal College of Psychiatrists blames social media for this unprecedented rise.While some "pro-ana" (pro-anorexia) sites claim to provide a neutral forum for sufferers, others brazenly assert that anorexia is a lifestyle choice, not a medical condition - and that the individual's decision not to eat should be respected. (A sample post from a young girl: "I convinced my parents to let me go vegan so now all I eat during dinner is vegetables if I even eat at all :) Stay f****** strong and skinny! Starve on.")Who runs these sites, and what their motivation might be, is anyone's guess. The fact that they exist, unregulated, and accessible to any teenage girl (or boy) is a scandal.Eating disorders are addictive, and self-starvation becomes involuntary. Anorexia has the highest mortality rate of all mental illnesses.Meanwhile, a form of disordered eating known as orthorexia is becoming more mainstream, fuelled by the mania for healthy eating. Orthorexia is somewhere between being health conscious and a health obsessive. Disordered eating goes hand in hand with excessive levels of physical activity.Hardcore workouts have surged in popularity among middle-class women, who go for the burn at their "skinny-bitch collective" classes and then Instagram the results. - ©The Daily Telegraph, LondonThe fifth season is on BBC Lifestyle on DStv channel 174 on Saturdays at 9pm and Sundays at 8pm..