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. For example, a recent review detailed the myriad ways that certain carbohydrates can induce cardiovascular conditions such as heart attack and stroke [1].
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 glycemic index (GI) and/or glycemic load (GL) [2]. 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 [3]. 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 [BMI]) and body shape (waist circumference [WC]). Here's what they found:
In individuals with a BMI of 25 or more (traditionally regarded as "overweight"), women eating diets of the highest GI were at a 35 percent increased risk of breast cancer compared to those consuming diets of the lowest GIs.
In individuals with the highest WC, a high GI diet was associated with a 35 percent increased risk of breast cancer. In this group, a high GL diet was found to be associated with a 37 percent increased risk of breast cancer.
Overall, therefore, these results suggest that for individuals deemed "overweight," a diet rich in sugar and insulin-disruptive carbs is associated with an increased risk of breast cancer.
One potential explanation is that being overweight, particularly if any excess weight tends to accumulate around the midriff, may be a sign that carbohydrate is not well tolerated. In such individuals, there may be an enhanced tendency to see disruption in blood sugar and insulin 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 eating them 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 and GL carbs may reduce disease risk, and my experience is that it's generally effective for allowing individuals to shrink their waist size too.
References:
1. Brand-Miller, et al. The Glycemic Index and Cardiovascular Disease Risk.
Current Atherosclerosis Reports 2007; 9: 479–485
2. Sieri S, et al. Dietary glycemic index, glycemic load, and the risk of breast cancer in an Italian prospective cohort study American Journal of Clinical Nutrition 2007 86: 1160–1166
3. Lajous M, et al. Carbohydrate intake, glycemic index, glycemic load, and risk of postmenopausal breast cancer in a prospective study of French women. American Journal of Clinical Nutrition 2008; 87: 1384–91
Dr. John Briffa is a London-based doctor and author with an interest in nutrition and natural medicine.
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