Why does flaxseed promote breast growth?

Do foods rich in estrogen increase breast size?

Phytoestrogens have both anti-inflammatory and antioxidant properties regardless of their estrogen receptor (ER) binding effects. The latter action brings them under the class of Endrocrine Disruptors:

Probably the best characterized type of phytoestrogenic action is estrogen receptor binding (ER). There are two main mammalian ER subtypes, ERα and ERβ (also known as ESR1 and ESR2, respectively). As such, phytoestrogens, especially the isoflavones, conform to the Environmental Protection Agency's definition of an endocrine disruptor, which characterizes these compounds as those which "alter the structure or function (s) of the endocrine system and have adverse effects". This definition includes lactation disorder, timing of puberty, the ability to produce viable, fertile offspring, gender-specific behavior, premature reproductive senescence, and impaired fertility .... [1]

The effect on breast tissue is unclear. Infants do not have breasts as such, but [2]

The hypothesis that exposure to soy phytoestrogens at the beginning of life can alter the timing and character of breast development is supported by a cross-sectional study of 694 girls in Israel from 2008, which found an increased prevalence of breast buds in 2-year-old girls who were fed soy formula as infants

In adults, the situation is less clear.

Some researchers and clinicians fear that high phytoestrogen intake could increase the risk of carcinogenesis and expose breast cancer survivors to recurrence because they bind ERs with relatively high affinity. Others have suggested the opposite, citing traditionally low cancer rates in Asia as evidence [1].

The effect on breast cancer cells appears to be related to both dose and other factors

For example, genistein can inhibit the proliferation of ER-positive and ER-negative breast cancer cells in vitro at high doses (> 10 M), but paradoxically it can promote tumor growth at lower, more physiological doses [1].

This is similar to tamoxifen, a selective estrogen receptor modulator (SERM) used for breast cancer therapy

There are no studies examining its influence on breast size in adults , and the measurement itself is somewhat difficult to perform reproducibly.

[1] Patisaul HB, Jefferson W. The advantages and disadvantages of phytoestrogens. Front Neuroendocrinol 2010 Oct; 31 (4): 400-19. doi: 10.1016 / j.yfrne.2010.03.003. PubMed PMID: 20347861+.

[2] Zung A, Glaser T, Kerem Z, Zadik Z. Breast development in the first two years of life: an association with soy-based infant formula. J. Pediatr. Gastroenterol. Nutr. 2008 Feb; 46 (2): 191- 5. doi: 10.1097 / MPG.0b013e318159e6ae. PubMed PMID: 18223379.