Two approaches to boosting obese men's sperm have been presented at the annual meeting of the Endocrine Society. The first suggested that obese men who lost weight were more likely get their partners pregnant. The second found that a cancer drug helped some infertile men have children.

Experts said the approaches were interesting alternatives to IVF and were opening up "real possibilities" for men. Weight loss is already widely advised for women struggling to conceive and obesity has long been suspected as a factor in male infertility.

A team at the University of Sherbrooke in Canada say they have conducted the first study to help men lose weight and see if it improved the chances of conception. In 65 couples who had been referred to a fertility clinic, the men were sent to weekly group sessions on nutrition and physical activity for a year.

One of the researchers, Dr Jean-Patrice Baillargeon, said: "This is the first prospective study suggesting that male partners who improve their weight also increase the odds for the couple to conceive." He believes obesity could directly affect the sperm count, but may also affect the quality of sperm by subtly altering the DNA. And he added that both men and women should be encouraged to lose weight if they were trying for a baby.

The second study focused on the chemical letrozole, which has been used in breast cancer and as a fertility treatment in women. The excess fat in men can alter the balance of sex hormones, which in turn affects sperm count.Letrozole can stop testosterone being broken down into oestrogen. 

Trials took place on 12 men who had developed hypogonadotrophic hypogonadism, a form of infertility, as a result of their obesity. Two were able to have babies after being infertile for at least three years.

Dr Lena Salgado, from the University of Montreal, said: "Letrozole is a very attractive fertility treatment with obesity-related hypogonadism."