High GI/GL carbohydrates again linked with an increased risk of breast cancer

Because for so long we have been encouraged to eat a diet based on carbohydrates, it’s natural to have warm feelings toward this ‘macronutrient’. Yet, many carbohydrates, particularly those that cause considerable fluctuation in blood sugar and insulin levels, I think should be handled with considerable caution.

Not that long ago, I blogged about a recent review which highlighted the link between the eating of disruptive carbs and cardiovascular disease.

Another condition which has been linked with the intake of disruptive carbs is cancer. Some cancers, notably cancer of the breast, has been found to be more common in individuals who eat a diet rich in food of relatively high glycaemic index (GI) and/or glycaemic load (GL). For more on this evidence, see here.

I was interested to read a recently-published study which revisited this topic. Published in the American Journal of Clinical Nutrition, this research assessed almost 63,000 post-menopausal women over a 9-year period [1]. The researchers assessed the relationship between total carbohydrate intake, overall dietary GI and GL, and risk of breast cancer.

Overall, there was no apparent significant relationship between any of the dietary measures and risk of breast cancer. However, the researchers went further by assessing whether or not any relationship between diet and breast cancer risk could have any further relationship with the body weight (body mass index) and body shape (waist circumference). Here’s what they found:

In individuals with a body mass index of 25 or more (traditionally regarded as ‘overweight’), women eating diets of the highest GI were at a 35 per cent increased risk of breast cancer compared to those consuming diets of the lowest GIs.

In individuals with the highest waist circumference, a high GI diet was associated with a 35 per cent increased risk of breast cancer. In this group, a high GL diet was found to be associated with a 37 per cent increased risk of breast cancer.

Overall, therefore, these results suggest that for individuals deemed ‘overweight’, a diet rich in sugar/insulin disruptive carb is associated with an increased risk of breast cancer.

One potential explanation here is that being overweight, particularly if any excess weight tends to accumulate around the mid-riff, may be a sign that carbohydrate is not well tolerated. In such individuals, there may be a generally enhanced tendency to see disruption on blood sugar/insulin in response to whatever carbohydrate is eaten compared to individuals of lower weight and smaller waist size. The relevance of this is that higher insulin levels as well as related substances called insulin-like growth factors have been associated with an increased risk of breast cancer.

This study provides further support for the idea that certain carbohydrates are far from benign in terms of their effects on health, and that they’re eating may predispose towards a range of conditions (including breast cancer). This study suggests that individuals carrying extra weight around the middle may be at particular risk. The good news is that cutting back on high GI/GL carbs may reduce disease risk, and my experience is that it’s generally effective for allowing individuals to shrink their waist size too.


1. Lajous M, et al. Carbohydrate intake, glycaemic index, glycaemic load, and risk of postmenopausal breast cancer in a prospective study of French women. Am J Clin Nutr 2008;87:1384-91

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