Glucose metabolism
Refined sugar is a high energy, low nutrient food – junk food. "Unrefined" sugar (honey, evaporated cane juice, etc) is also very concentrated and is likely to contribute to the same problems as refined sugar. Refined wheat flour products are lacking the wheat germ and bran, so they have 78 percent less fiber, an average of 74 percent less of the B vitamins and vitamin E, and 69 percent less of the minerals (USDA Food database, data not shown). Concentrated sugars and refined flour products make up a large portion of the carbohydrate intake in the average American diet. One way to measure the impact of these foods on the body is through the glycemic index.
The glycemic index is an indication of the blood sugar response of the body to a standardized amount of carbohydrate in a food. The glycemic load takes into account the amount of food eaten. An international table of the glycemic index and glycemic load of a wide variety of foods has been published [11].
Case-control studies and prospective population studies have tested the hypothesis that there is an association between a diet with a high glycemic load and cancer. The case control studies have found consistent increased risk of a high glycemic load with gastric [12], upper aero digestive tract [13], endometrial [14], ovarian [15], colon or colorectal cancers [16,17]. The prospective studies' results have been mixed. Some studies showed increased risk of cancer in the whole cohort with high glycemic load [18-20]; some studies found only increased risk among subgroups such as sedentary, overweight subjects [21-24]; other studies concluded that there was no increased risk for any of their cohort [25-28]. Even though there were no associations between glycemic load and colorectal, breast, or pancreatic cancer in the Nurses' Health Study there was still a strong link between diabetes and colorectal cancer [29].
Perhaps the dietary glycemic load is not consistently related to glucose disposal and insulin metabolism due to individual's different responses to the same glycemic load. Glycated hemoglobin (HbA1c) is a time-integrated measurement of glucose control, and indirectly, of insulin levels. Increased risk in colorectal cancer was seen in the EPIC-Norfolk study with increasing HbA1c; subjects with known diabetes had a three-fold increased risk of colorectal cancer [30]. In a study of a cohort in Washington county, Maryland, increased risk of colorectal cancer was seen in subjects with elevated HbA1c, BMI > 30 kg/m2, or who used medications to control diabetes [31]. However, glycated hemoglobin was not found to be associated with increased risk of colorectal cancer in a small nested case-control study within the Nurses' Health Study [32]. Elevated fasting glucose, fasting insulin, 2 hour levels of glucose and insulin after an oral glucose challenge, and larger waist circumference were associated with a higher risk of colorectal cancer [33]. In multiple studies diabetes has been linked with increased risk of colorectal cancer [34-37], endometrial cancer [38], and pancreatic cancer [35,39]. It is clear that severe dysregulation of glucose metabolism is a risk factor for cancer. Foods which contribute to hyperinsulinemia, such as refined sugar, foods containing refined sugar, and refined flour products should be avoided and eliminated from a cancer protective diet.