Postmenopausal women who consume a high-carbohydrate diet with a high glycemic load (GL) are at increased risk of developing estrogen receptor-negative and ER-negative/progestin receptor-negative breast cancer, according to a newly published study in the American Journal of Clinical Nutrition.
Investigators analyzed data derived from a subset among 334,849 women evaluated in the European Prospective Investigation into Cancer and Nutrition. Lead author Isabelle Romieu of the Nutrition and Metabolism Section of the International Agency for Research on Cancer in Lyon, France, and her colleagues analyzed data from 11,576 breast cancer cases (for which ER status was known in 63 percent), as well as additional information on PR and human epidermal growth factor receptor 2 (HER2) status. Subjects were followed for 11.5 years at 23 centers in 10 countries in Western Europe.
There is "scant" data on the relationship between carbohydrates; glycemic index (GI), which measures carbohydrate quality; and GL, which measures the quality and quantity of dietary carbohydrates, and the few studies that have attempted to investigate a possible association with breast cancer have yielded conflicting findings, the authors wrote.
Inconsistency in the results may be linked in part to a lack of power to evaluate the relation of dietary factors on specific breast cancer phenotypes on the basis of receptor status… To our knowledge, this is the largest study to date to explore this association with information on receptor status.
Investigators observed a positive association between GL and digestible carbohydrates and ER-negative and ER-negative/PR-negative breast tumors among postmenopausal women (but not among premenopausal women and other types of breast cancer).
The biological mechanism for the observed different associations with breast cancer jointly defined by ER and PR status is unclear, according to the study. A recent pooled analysis found that IGF-I was significantly related to ER-positive tumors.
"Our analyses suggest an association with ER-negative tumors, for which a mechanism distinct from the IGF-I pathway might be involved," the authors wrote. "Insulin could play a direct role by stimulating insulin breast receptors in breast tissue," and other mechanisms may be involved.
In stratified analyses, increased risk was associated with low dietary fiber intake, particularly among postmenopausal women. "This supports the hypothesis of a role of fiber in modifying carbohydrate absorption and in lowering insulin response." Further research is needed to confirm these results and "to better understand the mechanisms by which insulinogenic diets might increase the risk of receptor-negative breast tumors."
To a great extent, these findings simply reinforce what we already know: We all should strive to eat a balanced diet that limits refined carbohydrates and sweets and includes lean protein, vegetables, essential fatty acids, and high-fiber grains. But the message may now have more urgency for postmenopausal women. ER-negative tumors, which account for about a quarter of breast cancers, typically have a poorer prognosis than ER-positive cancers, because they tend to grow faster and are not sensitive to hormone-based therapies.
- Romieu I, Ferrari P, Rinaldi S, Slimani N, Jenab M, et al. Dietary glycemic index and glycemic load and breast cancer risk in the European Prospective Investigation into Cancer and Nutrition (EPIC). Am J Clin Nutr. 2012 Aug;96(2):345-355. Epub 2012 Jul 3.