Soy Many Opinions!

May 6, 2014
Rebecca Bechhold, MD
Rebecca Bechhold, MD

Oncologists are always queried about how to “eat better so my cancer doesn’t come back.” I have found the most common food issue to be the role of soy in the diet, particularly for hormone-driven breast and prostate cancer patients.

Amazing what a panic this little bean can cause. There are hundreds of articles out there, but the “evidence” presented makes it the savior food or equates it to soylent green. Neither is correct in my opinion.

Oncologists are always queried about how to “eat better so my cancer doesn’t come back.” I have found the most common food issue to be the role of soy in the diet, particularly for hormone-driven breast and prostate cancer patients.

One breast cancer patient’s husband brought me a bottle of salad dressing one day. He was literally teary-eyed. I was a bit nonplussed as everyone knows I prefer chocolate chip cookies. He was newly diagnosed with prostate cancer, and from reading on the Internet “learned” that he must eliminate all soy products from his diet. This was his favorite dressing, but it had soybean oil in it so he wanted to give it away. I am still not sure if this was a nice gesture or a way of wishing me a similar fate. Anyway, we had a nice long chat, and he went home with his salad dressing and a better outlook.

A number of years ago, a noted breast cancer expert came to our institution for a discussion. I distinctly remember her saying that when she experienced hot flashes, she loaded up on soy powder in her daily shake. I used to repeat her advice to patients, noting the source of that recommendation. I think her enthusiasm has tempered. But soy is no villain. You know my mantra-all things in moderation.

It is important for all of us to understand how soy does and does not affect our cancer patients so that we can offer sound guidance when this question comes up-and it will. No reason to duck out the door with a mumbled “see you in 6 months” when your opinion is solicited.

Soybeans are an excellent source of protein with no fat or cholesterol. Soy can be consumed in a myriad of ways, including tofu, edamame, milk, miso, and powder. And if you haven’t had soy hummus, try some-delish with carrots! The controversy comes in the fact that soy is full of isoflavones, which are weak plant estrogens. But they are really more like plant selective estrogen receptor modulators. The “estrogen” activity is not nearly on par with the hormone we produce in ovaries or adrenals. So, maybe it actually displaces the estrogen on the receptor. It certainly is not conjugated estrogen.

There are studies suggesting that Asian women have fewer instances of breast cancer because they eat such large quantities of soy. The Shanghai Breast Cancer Survival Study, published in the Journal of the American Medical Association in 2009, followed over 5,000 breast cancer survivors and looked at soy food intake and breast cancer recurrence and deaths. They found that “soy food intake…was inversely associated with mortality and recurrence…The inverse association was evident among women with either estrogen receptor (ER)-positive or ER-negative breast cancer and was present in both users and non-users of tamoxifen.”[1]

Does this mean our patients should be pounding soy shakes twice a day? Decidedly not.

The Shanghai study makes me feel confident my patients can eat soy. But it is the quality of the soy that I think is misunderstood. As I understand Asian diets, they do eat soy but in relatively small amounts, and it is pure soy, not processed soy that we often see here. Just like the American Society of Clinical Oncology campaign-choose (your soy) wisely. You want to partake of whole fermented soy. Be more sparing with processed soy, like the milk or soy protein in powder and energy bars. You can find whole bean soy milk. The website wellandgoodnyc.com recently reviewed nutrition bars and noted that one popular bar (that I used to enjoy) provided all of its protein from soy isolate and it would make one “bloated and gassy.” While you are reading labels, remind patients to look for what is added to the milk-many have preservatives, syrup, and sugar. No big deal if you just throw a spot of it into your morning joe, but you probably don’t want to drink large quantities.

So in conclusion, yes to real soy, yes to moderation. As the tag line reads, “please enjoy responsibly.”

References:

1. Shu XO, Zheng Y, Cai H, et al. Soy food intake and breast cancer survival. JAMA. 2009;302:2437-43.