Knowing that several studies had drawn links between a history of weight gain and increased breast cancer risk, Belgian researcher Jaak Janssens (Limburg University Centre, Diepenbeek) wondered whether the boom in sugary soft-drinks might be a factor, as drinking these cause insulin levels to soar. His hypothesis is that inappropriate levels of insulin in the body at a critical phase in breast development could lead to lesions which could, later, become cancerous.

To test the link between soft drinks and insulin secretion he persuaded teenagers to fast for 12 hours then drink a 330ml bottle of a popular fizzy drink. Insulin levels did indeed soar and, interestingly, the greater the amount of body fat, the higher the insulin went. He suggests that there is a vicious circle. "Soft drinks and high calorific food in pubertal children brings accumulation of body fat and in turn increases the response of insulin". This could decrease the body's overall sensitivity to insulin, which may have a continuing effect on breast cells. He believes that a similar process could explain the increase in testicular and prostate cancer.

This hypothesis is backed by a 10 year study on the link between high insulin levels and breast cancer