Our obsession with food - whether we eat too much sugar, too much over-processed and genetically modified food, whether to "go organic" - seems to be producing a new eating disorder. Orthorexia nervosa, which describes an unhealthy fixation with the purity and quality of food, can cause severe and dangerous weight loss, but more often it leads merely to social isolation, as orthorexics won't eat everyday dishes.
If you eat out in restaurants with friends you will understand the scale of the epidemic. More and more of us are specifying particular ingredients or the strict removal of others, or interrogating exasperated waiters about how the dishes are prepared and where the ingredients come from.
Middle-class dinner parties all over the country are being wrecked by guests with "special dietary requirements".
But orthorexics aren't all fussy faddists with imaginary food intolerances.
There are many serious sufferers who devote enormous mental energy and many hours to searching out "pure" food. In the United States, one of the first patients diagnosed with the condition died of heart failure brought on by orthorexia-induced starvation.
The results of a study carried out by the Institute of Gut Sciences at La Sapienza University in Rome have just been published in the academic journal Eating and Weight Disorders. The researchers found that up to 7 per cent of Italians suffer from orthorexia nervosa, a staggeringly high figure for a such a newly diagnosed disorder.
And it seems that the condition is a classic example of a little education being a bad thing: sufferers appear over-confident in what they know about nutrition and are driven by panic and fear to behave, paradoxically, in an unhealthy way. Every day doctors face patients who think they are experts.
Maybe at the heart of a good education is humility; an ability to understand the limits of our knowledge. But how often do teachers admit in the classroom that there are gaps in what they know? Perhaps they are afraid that if they make such an admission, students will lose confidence in the little knowledge they are trying to impart. But we don't want our students to be over-dependent on their teachers; we want them to find things out for themselves. However, these days that often involves nothing more than a quick trawl of the web. And there's plenty of stuff out there to convince the healthiest person that they're ill.
Dr Raj Persaud is Gresham professor for public understanding of psychiatry, and director of the Centre for Public Engagement, King's College London.
His latest book is The Motivated Mind (Bantam Press). Email: email@example.com