Breast Cancer & Sugars
A joint study performed by researchers from Mexico’s Instituto Nacional de Salud Publica and Harvard University found a correlation between high sugar intake and breast cancer. The study also looked at fat intake and found no evidence that a high amount of dietary fat contributes to breast cancer. The case-control study involved 475 women with breast cancer (ages 20 to 75 years), diagnosed at six Mexico City hospitals, and 1,391 controls from Mexico City. Each participant answered questions about sociodemographic variables and potential breast cancer risk factors and completed a validated food frequency questionnaire. Those with cancer were interviewed before the diagnosis was confirmed, which reduced the likelihood of dietary changes due to illness. Women living in Mexico City tend to eat more carbohydrates and less fat and animal protein than those living in affluent Western countries. Although the incidence of breast cancer is lower in most parts of South America than in the US, most areas are seeing an increase. The researchers found a significant relationship between cancer risk and carbohydrate intake as well as sucrose intake and cancer. Although carbohydrate intake among Mexican women has been traditionally high (64% of energy), the study notes that obesity has “greatly increased” in recent years. The study does not specify the types of carbohydrates being eaten. Although the researchers were unable to calculate glycemic index and look at this relationship to breast cancer, the researchers did have data on insoluble fiber intake. Fiber is believed to restrain carbohydrate absorption, affecting glycemic response. The researchers report, “The strength of the association between sucrose intake and risk for breast cancer was lower among women in the highest tertile [third] of insoluble fiber intake when compared with women in the lowest tertile of insoluble fiber intake.” When the researchers looked at specific types of fats, they found that neither saturated nor monosaturated fat intake showed any association with breast cancer risk. Polyunsaturated fats showed a protective effect, as it was “inversely related to the overall risk of breast cancer, particularly among postmenopausal women.” (The food source for these fats was not given.) The researchers note that polyunsaturated fat intake among Mexican women is about half that of people in the US. The researchers say, “The lack of a significant overall association between total fat intake and breast cancer risk in this study is consistent with the analysis of prospective studies of diet and cancer.” The authors of this study hypothesize that high insulin levels that result when eating starch or sucrose (high glycemic foods) may contribute to breast cancer in several ways. First, high insulin levels caused by eating these foods may increase the availability of insulin-like growth factor (IGF) by reducing the number of proteins that bind to it. IGF-l, which can increase cell proliferation, has been linked to an increased risk of premenopausal breast cancer. Ninety percent of breast tumors are insulin receptor positive and overexpress IGF-l. Insulin and IGF-l also have an effect on sex hormone levels, which have been thought to have a role in breast cancer. Both stimulate the ovaries to make sex hormones. They also impair the liver’s synthesis of the sex hormone binding globulin, which results in higher levels of free estrogens and androgen in circulation.
Romieu I, Lazcano-Ponce E, Sanchez-Zamorano LM, Willett W, Hernandez-Avila M. Carbohydrates and the Risk of Breast Cancer among Mexican Women. Cancer Bpidemio; Biomarkers Preu 2004;13(8). August 2004