The Great Soy Debate
You've heard both sides- soy is good for you, soy is bad for you. For each research study that comes out saying that soy helps prevent cancer another one comes out suggesting that soy consumption increases you risk for breast cancer. So where all of this coming from and what are you suppose to believe?
The compounds in soy responsible for their effects on health are called isoflavones. Isoflavones are bioactive compounds that may play a role in various health outcomes such as improved health of arteries and prevention of certain cancers (1). Ironically, it is these same compounds that have been speculated to contribute to breast cancer in cell and animal studies.
Isoflavones are considered to be possible selective estrogen receptor modulators, meaning that, under certain experimental conditions, they can exhibit "estrogen-like" effects (1). But let's get one thing straight: Foods made with soy actually do not contain estrogen. Although isoflavones are found naturally found in soy, they are plant "phytoestrogens". While they look similar in chemical structure to estrogens, they act very differently in the human body and shouldn't be confused with the human hormone estrogen. Various supplements and isoflavone extracts often used for the treatment of menopausal symptoms and for the prevention of age-associated conditions such as cardiovascular diseases and osteoporosis in postmenopausal women (2). Concern began when studies in breast cancer survivers began to show evidence that Genistein, the primary isoflavin in soy, promoted tumor growth (3). However, there are also studies done that suggest the protective benefits of genistein and soy for breast cancer prevention.
A recent review done on Soy isoflavones, estrogen therapy, and breast cancer risk concluded:
"Overall, there is little clinical evidence to suggest that isoflavones will
increase breast cancer risk in healthy women or worsen the prognosis of breast
cancer patients (1)." Furthermore, there is sparse evidence for any clear cut estrogen-like or anti-estrogen effects of dietary intake soyfoods or isoflavones on human breast tissue (4). While more research is needed to rule out all concerns, the existing
data can provide a degree of assurance that isoflavone exposure at levels
consistent with previous dietary intake studies, does not result in adverse
stimulatory effects on breast tissue.
Other primary concerns with soy include changes in other reproductive hormones such as testosterone. With regard to testosterone, a large review of the available research on the effect of soy consumption on testosterone levels and other reproductive hormones concluded that neither soy protein nor soy isoflavones affect reproductive hormone concentrations (5).
The good news
about soy is that it is considered to be a complete protein and can be a great
option for vegetarians and individuals with lactose intolerance. Also,
consumption of soy milk can have additional benefits for bone mineral density
in women. Various animal studies have shown the bone sparing effects of the
isoflavins found in soy protein, and many recent studies show promising effects
in humans as well (6). Specifically, spinal bone mineral density in
post-menopausal women has been positively correlated with isoflavins,
suggesting 83 mg of isoflavones daily to experience these results (7). One cup
of soy milk contains 20-40 mg of isoflavins, so one could achieve this amount
in 2-3 cups of soymilk. The science behind this idea is that non-steroidal
isoflavins selectively bind to estrogen receptors and stimulate osteoblast
activity while inhibiting osteoclast activity, resulting in reduced bone
turnover (6).
1) Messina, M. & Wood, C. (2008). Soy isoflavones, estrogen therapy, and breast cancer risk: analysis and commentary. Nutrition Journal, 3, 7-17.
2) Andres, S., Abraham, K. Appel, K., & Lampen, A. (2011). Risks and benefits of dietary isoflavins for cancer. Critical Reivew of Toxicology, 41(6), 463-506.
3) Messina, M. & Loprinzi, C. (2001). Soy for breast cancer survivors: a critical review of the literature. Journal of Nutrition, 131(11), 3095-3108.
4) Yildiz MF, Kumru S, Godekmerdan A, Kutlu S. (2005). Effects of raloxifene, hormone therapy, and soy isoflavone on serum high-sensitive C-reactive protein in postmenopausal women. Int J Gynaecol Obster, 90 128-133.
5) Hamilton-Reeves JM, Vazquez G, Duval SJ, et al. (2010). Clinical studies show no effects of soy proteins or isoflavones on reproductivehormones in men: results of a meta-analysis. Fertil Steril. 94:997-1007.
6) Lydeking,
E, Jens, O, Beck, E, and Jenson, K. (2004). Soymilk or progesterone for
prevention of bone loss. European Journal of
Nutrition, 43(497), 246-257.
7) Newton, K., LaCrois, A., Levy, L. Li, S., Qu, P. & Potter, J. (2006). Soy protein and bone mineral density in older men and women: a randomized trial. Maturitas, 55(3),270-277.
