Thin women risk infertility

Kay Brennan Leeds

Women who keep their body fat to a minimum, so they can be fashionably thin, could be putting their fertility at risk, according to a US expert. In Female Fertility and the Body Fat Connection, a new book, Professor Rose Frisch looks at fertility, body fat, and reproductive health; she suggests women who are too lean are risking infertility.

Professor Frisch, associate professor of population sciences emeritus at the Harvard Medical School of Public Health, Boston, has devised a critical fatness theory after over a decade of work in the area. The theory connects body mass index with fertility: if the index drops to 18 or 19 then ovulation stops. This can go unnoticed as a woman's periods may continue with no change; at indices of less than 18, however, periods will often stop altogether.

Frisch highlights the danger of being borderline underweight, and says that a loss of only 1.4 kg, for a normal sized woman, could lead to infertility, without any outward signs.

Frisch believes that women should not be ashamed of having body fat: "Fat converts the male hormone androgen into the female hormone oestrogen and is, therefore, a key part of a women's reproductive ability: it is something that should be celebrated. My work proves scientifically how important body fat is to a woman's health."

Frisch used magnetic resonance imaging to assess how much fat was in a womans' body. She compared female rowers' thighs with those of more sedentary women of the same age and found that the rowers had a great deal more muscle, 30% to 40% less body fat, and no menstrual cycle.

Fertility experts have commented that leanness is not the only factor that affects fertility: stress and exercise should also be taken into account. Mr Adam Balen, consultant gynaecologist at Leeds General Infirmary specialising in infertility and a spokesman for the British Fertility Society, told the studentBMJ, "There is a modern desire among women to be thin, and this means many keep slightly underweight by eating low fat foods and overexercising. The good news is that if they gain weight their fertility will be restored."

Balen warned of the damage, however, to long term health, "Low oestrogen levels when a woman is young will reduce the density of her bones. It will not be restored even if weight is gained, putting her at greater risk of osteoporosis in the future."



studentBMJ 2002;10:215-258 July ISSN 0966-6494