Table 3.

Main findings on the association between soy intake and breast cancer risk.

Author (Year) [Ref]	Food/Intervention under Investigation	Type of Study	Participants	Assessment of Dietary Intake	Main Results
Wada K et al. (2013) [23]	Soy and isoflavones	Prospective cohort study	15,607 women	FFQ	A negative association between soy and isoflavone intake and breast cancer risk was observed solely in post-menopausal women.
Li L et al. (2013) [46]	Isoflavone	Case-control study	1120 controls	FFQ	A protective effect of dietary isoflavone intake on breast cancer development was reported for both hospital outpatient and population controls.
Ko KP et al. (2013) [55]	Soy, vegetables, fruit, meat, and seafood	Case-control study	2271 women	FFQ	Negative association between soy consumption and breast cancer risk in BRCA carriers
Chen M et al. (2014) [51]	Soy and isoflavone	Meta-analysis	1,391,524 pre-menopausal and 579,33 post-menopausal women	n.d.	An inverse association was found between soy isoflavone intake and breast cancer incidence, independently of menopausal status, solely in Asian women.
Woo HD et al. (2014) [52]	Soy products, fruits, and vegetables	Meta-analysis	8112 participants	n.d.	Different kinds of soy foods were inversely associated with breast cancer risk in both pre-menopausal and post-menopausal women.
Wu J et al. (2016) [45]	Meat, soy, milk, yogurt, poultry, fish, eggs, and nuts	Meta-analysis	452,916 participants	n.d.	Reduced breast cancer risk with high soy consumption.
Zhao TT et al. (2017) [48]	Soy and isoflavone	Meta-analysis	648,913 participants	FFQs, self-administered questionnaires, and mail survey questionnaires	A statistically significant inverse association was shown between high versus low soy consumption and breast cancer risk.
Tan MM et al. (2018) [42]	Soy, breastfeeding, and PA	Case-control study	7663 women	Interviews and FFQs	High soy milk and soy product consumption demonstrated an inverse association with breast cancer incidence.
Wei Y et al. (2020) [43]	Soy and isoflavones	Prospective cohort study and meta-analysis	30,0852 women for the cohort study and 513,313 participants for the meta-analysis	FFQs, physical measurements, resurveys, 24-h dietary recalls	The cohort study revealed no association between moderate or high soy consumption and breast cancer. The meta-analysis showed a 3% reduced risk of breast cancer development with each 10 mg/day increase in isoflavone intake.
Wang Q et al. (2020) [49]	Tofu	Meta-analysis	109,813 participants	n.d.	A protective effect of tofu consumption on breast cancer development was observed independent of menopausal status.
Okekunle AP et al. (2020) [53]	Soy and isoflavone	Meta-analysis	29,810 participants	n.d.	Increased soy consumption reduced breast cancer risk, especially in pre-menopausal women and for ER-negative subtype development.
Lu LW et al. (2022) [24]	Isoflavones versus placebo	Clinical trial	194 pre-menopausal women	N.A.	The authors found a decrease in breast tissue density with higher isoflavone intake, especially in pre-menopausal women.
Boutas I et al. (2022) [44]	Soy and isoflavones	Meta-analysis	485,495 participants	FFQ	High soy consumption reduced the breast cancer risk in pre- and post-menopausal women.
Cao S et al. (2022) [54]	Vegetable-fruit-soy dietary pattern	Case-control study	1753 women	FFQ	Higher soy consumption reduced breast cancer development in post-menopausal women, especially ER- and ER-/PgR-negative subtypes.
Shin S et al. (2023) [47]	Fruits, vegetables, meat, soy, green tea, alcohol	Meta-analysis	216,216 participants	n.d.	A protective effect of soy protein and isoflavone intake on breast cancer incidence was observed, but no correlation was found with soy food consumption.
Rajaram N et al. (2023) [50]	Soy isoflavone supplement versus isoflavones from dietary sources	Clinical trial	90 women	FFQ	Moderate and high intake of soy reduced mammographic density in both pre-menopausal and recently menopausal women.