The other day Claudette posted a request for skincare product recommendations that would be safe and effective for someone recovering from breast cancer. She specifically pointed out that soy extract was controversial and she wanted to avoid. Only a week earlier, I had received a bottle of Soy Rejuvenating  Serum by Reviva Labs, aimed at menopausal skin and accompanied by a pages-long essay on why soy is an anti-wrinkle breakthrough.

So is soy friend or foe? The answer seems to be a bit of both, although neither conclusion is as clear as we might like them to be.

Soy isoflavones are a class of estrogen-like compounds – the isoflavones genistein and daidzein - that have become widely used among postmenopausal women as a ‘natural’ alternative to hormone replacement therapy (Duncan et al. 2003). However, scientists report mixed results.

Soy does seem to provide some relief from hot flashes. A study with patients taking soy extract had a 61% reduction in their daily hot flashes versus a 21% reduction with a placebo. The findings were confirmed by a larger 2009 study. However, other researchers say that soy protein and isoflavones have not been shown to lessen vasomotor symptoms of menopause, and results are mixed with regard to soy's ability to slow postmenopausal bone loss. (source)

The concerns that Claudette referred to arise from studies of on mice that have demonstrated the ability of genistein and soy proteinto stimulate the growth of breast cancer cells in a dose-dependent manner (Allred et al. 2001Ju et al. 2001). However, further studies have shown slightly different results.  Ju et al.(2006) reported that dietary daidzein only slightly stimulated the in vivo growth of estrogen-dependent human breast tumor. And a study in 2007 raised concerns about the consumption of isoflavone supplements but reported no problems were detected with a topical serum.

The evidence that soy may actually prevent certain types of cancer doesn’t seem to be convincing. It has been described as “meager and cautionary with regard to a possible adverse effect”, leading to the conclusion that isoflavone supplements in food or pills are not recommended (source). Ultimately, as the Linus Pauling Institute puts it: “the effects of high intakes of soy isoflavones on breast cancer recurrence and survival of breast cancer patients have not been well studied. “

So what of soy as a topical solution against aging skin? The theory is that estrogen reduction accelerates photoaging and the formation of wrinkles. Estrogen also affects secretion by the sebaceous glands.

There are a few studies that suggest that it is promising.  In 2004, European researchers found that soy extract resulted in increased collagen and HA synthesis and “appears to rejuvenate the structure of mature skin”.

Another test on pigs (their skin is similar to that of humans when it comes to getting sunburned) showed that topical isoflavones provide UV protection. However, the protection was less than that provided by a topical combination antioxidant standard containing 15% L-ascorbic acid, 1%α-tocopherol, and 0.5% ferulic acid.

Reviva’s Soy serum is still on my desk. Well, I haven’t yet come across evidence that a topically applied phytoestrogen increases the risk of cancer. So in conclusion, I’d be willing to give it a try.