Low-fat dieters 'risk infertility'

Women who chain themselves to ultra low-fat diets in an effort to stay slim are risking making themselves infertile, according to new research.

Diets of non-fat yoghurt, lettuce, pasta and diet drinks help thousands of women get the skinny look which dominates the catwalk. Yet a new book by Harvard University fertility expert Professor Rose Frisch claims women who are just a few pounds underweight can become infertile if their weight dips below a "razor-thin borderline".

Professor Frisch said: "My work proves scientifically how important body fat is to a woman's health. It is a wake-up call to all those women who believe that keeping super lean is the right thing to do."

In her book, Female Fertility And The Body Fat Connection, Professor Frisch points out that a healthy, normal-sized woman could be living on a borderline. Even an apparently minor extra weight loss, of around three pounds, could leave the woman unable to conceive. Professor Frisch criticises a fear of fat, claiming that a well-nourished woman should carry as much as 40 per cent body fat.

According to Professor Frisch, the brain will switch off a woman's reproductive abilities if she fails to maintain a high enough calorie intake. For a woman to carry through a pregnancy to full term her body needs to find an extra 50,000 calories above normal requirements.

She says that if a woman's body does not contain enough calories the brain will begin to restrict the flow of a hormone called leptin. Should the level of body fat dip below the threshold, a woman will carry on menstruating but without producing eggs. Further weight loss will stop her menstruating. If the reproductive system is turned off for too long there is a risk of permanent infertility.