As they head for the stomach from the mouth, the carbohydrates in vegetables, breads, fruits, and candy all begin breaking down into simple sugars. According to some studies, carbs with a low glycemic index (GI)—meaning that they are digested slowly—reduce a person’s risk of heart disease and obesity through an as yet unidentified mechanism linked to their effects on insulin (SN: 4/8/00, p. 236). Such low-GI fare may also offer protection against colon cancer, new research finds.

Insulin shepherds sugar into cells. The more sugar that’s deposited into the bloodstream at one time, the more insulin the body produces. Because this hormone can trigger the proliferation of colon cells, Livia S. Augustin of the National Cancer Institute in Aviano, Italy, decided to investigate the possible role of GI and related factors in colon cancer risk.

Her team surveyed the diet and eating habits of some 4,000 men and women from six different regions of Italy. Roughly half had colorectal cancer. The rest were cancerfree patients who had recently visited a local hospital.

The researchers computed GI values for all foods that each person regularly consumed. From those figures, they calculated a glycemic load for each individual—essentially a diet’s GI value adjusted for the amount of food in a typical meal. A high-GI diet generally included bread, cakes, sweets, and table sugar but few fruits or vegetables.

The colon cancer patients were twice as likely as the other people to regularly down high-GI foods and meals that put a high insulin demand on the body. Moreover, Augustin found, among people consuming high-GI foods most frequently, those who were overweight or ate relatively little plant-based fiber proved most likely to have colon cancer. She suggests that GI may help to explain the healthful effects of fruits and vegetables.

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