Glycaemic index, breast and colorectal cancer

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Abstract
Glycaemic index (GI) is an extension of the fibre hypothesis [1] and a ranking of carbohydrates based on their post-prandial blood glucose response [2]. The basic concept is that a higher rate of carbohydrate absorption leads to higher blood glucose and insulin rise, and hence a higher GI index. GI has been linked to non-insulin-dependent diabetes mellitus [3, 4], coronary heart disease, and also to excess risk of colorectal [5] and breast [6] cancer. Refined cereal intake has also been related to elevated risk of oral, oesophageal and laryngeal [7], and other digestive tract neoplasms [8]. The possible link is related to mutagenic and perhaps promotional effects of insulin and insulin-like growth factor (IGF) on the process of carcinogenesis [9–11]. Available data on GI and cancer risk are, however, extremely scanty. A multicentre case–control study from Italy found an odds ratio (OR) of 1.7 for colorectal cancer [5] and 1.4 for breast cancer [6] in the highest GI quintile, with significant trends in risk.