Eating a low-fat diet in adolescence may protect women against breast cancer, say researchers.

A study suggests it may lower levels of the sex hormone oestrogen which has been linked with breast cancer.

US scientists think diet may be crucial during puberty when breast tissue starts developing.

Experts say further work is needed to establish firm evidence.

Dr Peter Kwiterovich of The Johns Hopkins University in Baltimore, Maryland, helped carry out the work.

"A low-fat diet starting early in life may protect against breast cancer," he told BBC News Online. "But we don't yet have a definitive answer to that question."

Caution

High levels of oestrogen have been linked with an increased risk of breast cancer.

However studies in adult women have found no clear evidence that a high fat intake plays a role.

The latest research examined 286 girls aged between eight and 10 who were randomly assigned to either a conventional or a low-fat diet.

Levels of sex hormones in their blood were measured over the course of seven years.

At the end of the study, young women on a low-fat diet had 30% lower oestrogen levels.

Dr Tim Key, an expert on cancer and diet at the charity Cancer Research UK, said it was an interesting lead that needed to be followed up with more studies.

"This finding does not suggest that adolescent girls should alter their diet to try to reduce breast cancer risk," he warned.

The research is published in the Journal of the National Cancer Institute.