You probably already know that simple sugars and carbohydrates will cause an almost immediate rise in blood glucose levels. The problem with this scenario is that cancer cells have a voracious appetite for sugar. Nobel Prize winner Otto Warburg first discovered the connection in 1924, when his research revealed that cancer cells generate energy in a way that differs from normal cells, in a process called glycolysis. This process, he contended was so dependent on glucose that he dubbed tumors "obligate sugar metabolizers." "Cancer, above all other diseases, has countless secondary causes. But, even for cancer, there is only one prime cause. Summarized in a few words, the prime cause of cancer is the replacement of the respiration of oxygen in normal body cells by a fermentation of sugar." (Dr. Otto Warburg, Lecture delivered to Nobel Laureates on June 30, 1966 at Lindau, Lake Constance, Germany ) Among others, Warburg observed, and that observation has not been challenged in almost a century of subsequent research, that consuming sugars and simple carbs not only raises blood glucose rapidly, but the fast, abrupt nature of this increase triggers a healthy pancreas to responds by overproducing insulin, or order to bring levels down to normal range as quickly as possible. This initially healthy response, however, can lead to very unhealthy consequences. Insulin and its close relative, insulin-like growth factor (IGF-1) are cellular growth promoters (Hadsell, Bonnette. Journal of Mammary Gland Biology and Neoplasia. 2000). So each time you flood your bloodstream with insulin you are sending a message to your tumor: GROW!
It's clear that blood glucose and insulin levels have a pronounced effect on breast cancer survival statistics, a connection that has been documented for decades. For example, a mouse study conducted in 1985 indicated that higher blood glucose levels resulted in shorter survival times in mice with breast cancer, with the response being "dose dependent." In other words, the higher the blood glucose levels, the poorer the outcome. (Santisteban et al. Biochemical and Biophysical Research Communications. 1985)
What's critical to understand is that simple carbohydrates ("white" bread, rice, pasta, pastries, etc) convert to simple sugar within moments of your chewing them. Complex carbohydrates, those with intact fiber and germ release their glucose more slowly and more healthfully into the bloodstream.