Dietary Intake of Soy Protein and Tofu in Association With Breast Cancer Risk Based on a Case-Control Study

Abstract

Soy food and its constituents may protect against breast cancer, but the association between soy intake and decreased breast cancer risk is inconsistent. We evaluated the relationship between breast cancer risk and the dietary intake of soy protein as measured by total soy food and tofu intake. Histologically confirmed cases ( n = 362) were matched to controls by age (within 2 yr) and menopausal status. High soy protein intake was associated with reduced breast cancer risk in analyses adjusted for potential confounders including dietary factors among premenopausal women (odds ratio [OR] = 0.39 in the highest quintile, 95% confidence interval [CI] = 0.22–0.93, P for trend = 0.03) and postmenopausal women (OR = 0.22, 95% CI = 0.06–0.88, P for trend = 0.16). We also found an inverse association between total tofu intake and breast cancer risk among premenopausal women (for total tofu intake, OR = 0.23 in the highest quintile, 95% CI = 0.11–0.48, P for trend < 0.01; for at least 1 serving of tofu as the main ingredient per day, OR = 0.26, 95% CI = 0.13–0.55, P for trend < 0.01). We concluded that increased regular soy food intake at a level equivalent to traditional Korean consumption levels may be associated with a reduced risk of breast cancer, and this effect is more pronounced in premenopausal women.

ACKNOWLEDGMENT

This work was supported by Korea Ministry of Science and Technology (Grant No. M10418010002-05N1801-00210).

Notes

^a Abbreviations are as follows; N/A, not applicable; MET, metabolic equivalent.

^b N = 362.

^a Food items contributing to more than 5% of total energy-unadjusted soy protein intake were shown.

^b Sam jang is soybean paste with various seasonings such as garlic, scallions, green pepper, sugar, sesame oil, and so forth.

^c It is partial R ² from multiple stepwise regression with total soy protein intake as the dependent variable and soy protein from each variable as the independent variable.

^d P values were obtained by paired t-test.

^a Drinking (none, past, current), multivitamin use (yes, no), number of children, breast feeding (yes, no), and quintile of carbohydrate intake were included as covariates in multivariate Model 1. In addition to covariates in multivariate Model 1, dietary factors (quintiles of energy, vitamin E, and folate) were adjusted in multivariate Model 2.

^a n = 235 pairs.

^b n = 127 pairs.

^c Drinking (none, past, current), multivitamin use (yes, no), number of children, breast feeding (yes, no), and quintile of carbohydrate intake were included as covariates in multivariate Model 1. In addition to covariates in multivariate Model 1, dietary factors (quintiles of energy, vitamin E, and folate) were adjusted in multivariate Model 2.