Candy's not so dandy for the colon either

Eating foods with a high glycemic load increases colorectal cancer risk. Looking to insulin resistance for a cure

By Charles Rowe

"Current food guidelines that suggest you cut down on sugary, refined foods and bump up the whole grains, vegetables, and nuts are right on the money, " says Dr Susan Higginbotham. She's talking about reducing the risk of colorectal cancer, not merely your weight.

"This is the first prospective study to report a positive association between glycemic load and colorectal cancer, " says the physician/researcher.

She took part in the study, which appeared in the February 4 issue of the Journal of the National Cancer Institute, and found that women who eat a lot of food which quickly increases blood sugar levels are more likely to develop colorectal cancer than those who don't.

Colorectal cancer is the third most common cancer in Canada -- after breast and lung cancer in women and prostate and lung cancer in men. Over 17,000 new cases are diagnosed annually in Canada, and almost 7,000 people die.

Researchers headed by Dr Simin Liu of Harvard University analyzed data collected from women participating in the Women's Health Study. Begun in 1993, the study has assessed the influence of low-dose aspirin, vitamin E, and beta-carotene (since discontinued) on cardiovascular disease and cancer. Over 38,000 women aged 45 years or older have participated.

Carrying quite a load
Diet data from the preceding year was gathered when each woman entered the study, courtesy of a 131-item "food-frequency " questionnaire. Glycemic load is calculated based on the carbohydrates provided by food and how quickly they're metabolized. Foods with high glycemic load include candy and other sweets, refined flour products, pasta, and baked potatoes. An overall glycemic index was obtained for each person by dividing his or her glycemic load by the total carbohydrate intake.

Analysis of the diet and the age of cancer onset in 174 participants who developed colorectal cancer (148 had cancer of the colon and 26 had cancer of the rectum) showed that the cancer risk increased significantly as dietary glycemic load rose. Indeed, those whose diets produced the peak glycemic load were three times more likely to develop colorectal cancer, than those with low glycemic load diets.

This risk could well be underestimated, since risk factors such as high body mass index, a sedentary lifestyle, smoking, and drinking were not taken into account.

The researchers concluded that a diet with a high glycemic load might increase the cancer risk by affecting insulin and insulin-like growth factors. These diet-responsive compounds stimulate mitosis and cell growth in normal and cancerous colon epithelial cells.

As well, a high glycemic load could promote an inflammatory response via C-reactive protein, says Dr Higginbotham.

"The results mean that we may well have to understand the etiology of insulin resistance and diabetes before we can prevent colon cancer, " say Dr Bob Bruce of the University of Toronto, whose own research has implicated both insulin resistance and insulin itself in colon cancer promotion. Further work will be necessary to tease out these exact molecular details.