1. Introduction
cancer, deaths, breast cancer
CANCER, BREAST CANCER
Soy intake is associated with lower breast cancer risk in observational studies concerning Asian women, however, no randomized controlled trials (RCT) have been conducted among Asian women living in Asia. This three-armed RCT assessed the effects of one-year soy isoflavone (ISF) intervention on mammographic density (MD) change among healthy peri- and postmenopausal Malaysian women. This study was registered at ClinicalTrials.gov (NCT03686098). Participants were randomized into the 100 mg/day ISF Supplement, 50 mg/day ISF Diet, or control arm, and assessed for change in absolute and relative dense area from digital mammograms conducted at enrolment and after 12 months, compared over time across study arms using Kruskal-Wallis tests. Out of 118 women enrolled, 91 women completed the intervention, while 27 women (23%) were lost in follow up. The ISF supplement arm participants observed a larger decline in dense area (−1.3 cmGlobally, breast cancer continues to be the most common cancer in women and a leading cause of cancer-related deaths [Dietary interventions, such as soy intake, may be an important strategy for breast cancer risk reduction in this region. Asian populations with historically lower breast cancer incidence have soy-rich diets, up to 10-fold more compared to Caucasian women [To date, there are no intervention studies of soy isoflavones with breast cancer occurrence as the primary endpoint because it requires large cohorts followed over long periods of time, making such studies expensive and difficult. Instead, randomized controlled trials (RCTs) have tested interventions of 80–120 mg of soy isoflavones on biomarkers of breast cancer risk among Caucasian women, such as mammographic density (MD), but have consistently reported null or small effects [There are a few hypotheses that were proposed to explain the lack of a clinically meaningful effect in previous RCTs. First, the RCTs used purified and concentrated soy ISF supplements instead of traditionally consumed soy foods made from whole soybeans [Thus, we conducted a randomized controlled trial to determine if a soy ISF intervention, either consuming 100 mg/day of soy isoflavone supplement or 50 mg/day of soy ISFs through dietary sources of soy, could reduce breast cancer risk among peri- and post-menopausal Malaysian women, using MD as a biomarker of risk. To our knowledge, this is the first interventional trial of soy isoflavone intake, using both dietary and supplement sources of isoflavones, on breast cancer risk among Asian women living in Asia where soy foods are accessible, affordable, and palatable.