Poor diet early in life may predispose women to develop breast cancer, research has suggested.
A US study of young mice showed that a diet linked to obesity and harmful metabolic changes stimulated early breast growth. It also led to abnormal tissues in the breast that may produce breast cancer.
Lead researcher Dr Russ Hovey, from the University of California at Davis, said: "The findings of this study are particularly important when we superimpose them on data showing that girls are experiencing breast development at earlier ages, coincident with a growing epidemic of childhood obesity."
The scientists fed newly weaned mice a diet containing a fatty acid called 10,12 CLA which can trigger metabolic syndrome, a condition linked to obesity, diabetes and heart disease. The fatty acid is present in hydrogenated fats, widely used in the manufacture of biscuits, cakes and processed foods.
Giving female mice the 10,12 CLA stimulated growth of their mammary ducts. This was despite the young animals lacking the hormone oestrogen, believed to be vital to female reproductive development.
In some animals, the altered diet also resulted in the kind of abnormal cell growth that can lead to breast cancer.
The cancer link could be due to excess levels of insulin, the scientists believe.
Writing in the journal Proceedings of the National Academy of Sciences, they pointed out that postmenopausal women with raised insulin levels had an increased risk of breast cancer.
They concluded: "Our findings highlight a striking link between diet, metabolic dysregulation, and MG (mammary gland) growth that is independent of oestrogenic stimulation.
"These results lend support to increasing evidence suggesting a relationship between breast cancer risk and early life events that clearly include dietary components and their effects on aspects of metabolic dysregulation."