Possible link between low fiber diets and pre-menopausal breast cancer
 

In this retrospective analysis, pre-menopausal women who ate 30g of fiber a day had half the breast cancer risk of those who ate just 20g of fiber a day. There was no effect found among post-menopausal women.

http://news.bbc.co.uk/1/hi/health/6287915.stm

Of course this doesn't eliminate breast cancer, but halving it is a considerable reduction.

I ate a fairly high-fiber diet, so I guess I was just unlucky.