Objectives Some estrogen metabolites are associated with increased breast cancer risk, while others are protective. Research efforts have focused on modifiable factors, including bioactive compounds found in food or supplements, promoting estrogen profiles with anti-cancer properties. EstroSense® is a nutraceutical product with bioactive compounds, including Indole-3-carbinol and green-tea catechins, which may favourably affect estrogen profiles. This study was conducted to determine if EstroSense use, compared to placebo, promotes a higher urinary 2-hydroxyestrone:16α-hydroxyestrone ratio (2-OHE1:16α-OHE1), a biomarker associated with a lowered risk of breast cancer. Methods 148 premenopausal women were recruited from British Columbia, Canada to participate in a randomized, double-blind, cross-over, multicentre, placebo-controlled study in which women were randomized to a treatment sequence that consisted of either EstroSense®, followed by placebo or vice-versa. The women were instructed to consume three capsules per day of EstroSense® or the placebo for three menstrual cycles (∼12 weeks). The primary outcome was the measurement of 2-OHE1:16α-OHE1 in casual samples at baseline and after each treatment phase. Results After 12 weeks of intervention, the mean (95% CI) urinary 2-OHE1:16α-OHE1 was 4.55 (2.69, 6.42) (p<0.001) higher following EstroSense than placebo adjusted for baseline values. Conclusions EstroSense use led to markedly higher urinary 2-OHE1:16α-OHE1 than the placebo, a biomarker associated with a lower risk of breast cancer. Registration http://clinicaltrials.gov (NCT02385916).