High-Glycemic Foods Linked to Colon Cancer
Insulin Resistance Linked to Diabetes May Promote Colon Tumor Growth
What Is Glycemic Index? continued...
"This finding doesn't surprise me at all," says Marji McCullough, ScD, RD, nutritional epidemiologist and a senior researcher for the American Cancer Society. "The idea that insulin and its associated hormones elevate cancer risk is very plausible, and this mechanism is being actively studied in cancer research."
Already, she says, there is evidence that a diet rich in high-glycemic load foods can boost risk of pancreatic cancer, and there is some research -- which hasn't been verified -- that indicates these foods may also boost breast cancer risk.
As a general rule, low-fat, high-fiber foods -- fruits, vegetables, and whole grains and legumes -- often prescribed to manage weight and help prevent diabetes and other health conditions, have a low-glycemic index. Conversely, starchy and processed foods such as potatoes, breads, and cereals usually have a high-glycemic index.
Problem Hard to Pinpoint
"It's hard to pinpoint the real impact of a high-glycemic load diet, because it varies on a number of things, such as how much the food is processed, how big is the meal, and what other foods are in the meal," she tells WebMD. "If you have large portions, for instance, that also raises blood sugars very quickly."
These other factors may explain why the largest and longest study to date -- tracking nearly 50,000 Canadian women for 16 years -- found no link between intake of high-glycemic foods and future risk of colon cancers. That study was published last June.
"Because there have been very few studies of this issue to date, it is too early to make a final decision regarding an association with glycemic load to colon cancer," says Paul Terry, PhD, of the National Institute of Environmental Health Sciences in North Carolina, who led that study. "But the results of this study are interesting."
In Liu's study, some 40,000 American women filled out detailed questionnaires about their eating habits and their rates of colorectal cancers were tracked for nearly eight years. Overall, women consuming the most high-glycemic foods were three times more likely to develop colon cancers, but some women observed had a sixfold risk.