Dietary Fiber, Glycemic Index, and Glycemic Load in Relation to Breast Cancer in Iran

Background: Habitual consumption of diets with a high glycemic index (GI) and a high glycemic load (GL) may influence breast cancer, but consistent evidence is lacking in this regard. Objectives: In this hospital-based case-control study, we evaluated the contribution of GI, GL and dietary fiber to the risk of breast cancer in Iran, 2011-2012. Patients and Methods: Data on lifestyle, diet and family history were collected from the 87 newly diagnosed breast cancer premenopausal patients and 198 five-year agematched controls. Usual dietary intake was assessed by means of a 168-item semi-quantitative food frequency questionnaire (FFQ), which was interviewer-administered. Dietary average GI and GL were calculated by GI of Iranian food table and international tables of GI and GL values: 2008. Multivariate odds ratios (ORs) and 95% confidence intervals (CIs) for GI and GL intake were adjusted for age and major relevant covariates based on the review of literature. Results: Mean } SD GI was 59 } 17 among control patients and 70 } 16 among breast cancer cases; the corresponding numbers for GL were 159 } 45 and 189 } 44, respectively. The multivariate adjusted comparing the highest tertile of dietary GI and GL with the lowest tertile were 2.11 (95% CI 1.33-3.57; p-test for trend = 0.027) and 2.84 (95% CI 2.93-4.11; p-test for trend = 0.037) respectively with a significant trend. Fiber intake was suggestively inversely associated with breast cancer (OR = 0.79; 95% CI 0.34-0.88; p-test for trend = 0.015). Conclusions: Our results suggest that high dietary levels of GI and GL and low fiber intake may have unfavorable effects on breast cancer.