I have received hundreds of questions about soy and women's health. They include:
I'm pregnant and vegetarian and am trying to get enough protein in my diet. Is soy safe for me and my baby? I've heard it can cause hormonal problems and interfere with my nutrient absorption.
I've heard soy can cause thyroid problems.
I'm approaching menopause and am having horrible hot flashes. My doctor told me to drink soymilk butI'm just not sure that it’s safe.
My mom had breast cancer and I've heard that eating soy could increase my risk…
In the past decade, vegetarianism, including veganism, has become in vogue, and with this, soy has received a lot of positive – and negative – press. Touted health benefits include cholesterol reduction, the prevention of osteoporosis, heart disease, and cancer, and the prevention and treatment of menopausal symptoms. Yet critics have called it a “poison,” with the nutrition author Sally Fallon questioning whether soy is “the next asbestos.”
In a hurry? For my bottom line on soy, you can skip to the end of this article.
Bit of a health geek? Read on for the whole soy story…
Background: My Own Soy Odyssey
My first intentional encounters with soy were as a 15-year old vegetarian in 1981. I knew I needed protein and back then, the road to healthy eating wasn’t as clear as it is now and info was not as readily accessible. Tofu was an obvious choice – it was inexpensive, easily available, and packed a lotta' protein in a small amount. And it didn't require me to soak it and pressure cook it the way beans did.
Frankly, I pretty much hated tofu from the get-go, in just about all forms except the firm style, heavily seasoned with tamari and garlic. I’m still not a huge soy fan, though I pushed myself to eat it through my four vegetarian pregnancies to get enough protein for my growing babies. I don’t think it tastes that great, and it’s not the easiest food to digest. So I eat traditional forms, on rare occasion. I’ve always been a bigger fan of the other, and in my opinion, more flavorful beans such as black beans, garbanzos, and kidney beans, as well as nuts and seeds, for my protein.
As a mom raising 4 vegetarian kids, and through teaching thousands of patients how to eat healthy, plant-based diets over the past 25 years, including thousands of pregnant women, I’ve done quite a bit of research on the health benefits – and risks — of soy.
So what’s the deal? Is soy healthy? Dangerous? Somewhere in between? Many of you have written me with questions and concerns about soy and women's health. I found myself thinking: “Soy veh! I’d better write an article!” This piece will hopefully dispel your soy-confusion and give you some practical advice on whether and how to eat soy, safely.
Soy in the Diet
Soy has been a staple in the traditional Japanese diet for centuries. Okinawans, who consume more soy in their diets than any other people in the world, 1-2 portions daily, have more centenarians (folks alive over 100 years old) than any other culture on the planet. They also suffer lower rates of heart disease, osteoporosis, dementia, and breast cancer than Americans.
However, soy is only a small part of an overall healthy lifestyle. Okinawans eat all foods in moderation, following the Hara Hachi Bu rule of eating only to 80% full, and a low caloric intake diet is known to promote longevity. They eat a predominantly plant-based diet, with meats and traditional soy products as a complement, not an “entrée.”
They also exercise regularly, have psychospiritual practices that minimize stress, and have other lifestyle habits that promote health and longevity. So yes, traditional soy foods are a part of the equation of their healthy long lives, but only a small part.
Soy products can be divided into 3 main categories:
1. Traditional soy foods: Traditional forms of soy include tempeh, natto, miso, and tamari – all of which are fermented – tofu, and soymilk (yes, soy milk is a traditional food). Traditional daily soy intake appears to range from 25-40 g, roughly equivalent to 100-160 mg of isoflavones, the natural plant chemicals in soy that are thought to be beneficial to our health. In the US these foods are generally made from organic, non-GMO (genetically modified organism) soybeans.
2. “Frankensoy”: These are soy alternatives to common meat and dairy products, for example, tofu hot dogs, soy cheese, sweet soy milk in all sorts of flavors, soy yogurt, soy ice cream, soy bacon, soy sausage links, and soy burgers. Even when made from organic, non-GMO beans, these are generally highly processed soy junk foods and not part of a healthy diet. Soy protein isolates, often used to boost nutrition in protein shakes, and in menopausal supplements, are also, generally, forms of Frankensoy.
3. Processed, GMO, junk filler soy: Approximately 90% of the soy produced in the US is genetically modified to be resistant to herbicides, namely, Roundup, produced by Monsanto. Since soy is one of the most common ingredients in mainstream foods, this is a big deal!
There are many concerns about consuming genetically modified products. The two major health concerns about GMO soy are: 1) higher than legally allowable levels of pesticide residue remain on the crop, which we eventually ingest, and 2) the health effects of eating genetically modified products is unknown – it has even been raised as a health concern by Monsanto. GMO soybeans are nutritionally inferior to natural soybeans, and contain lower levels of the isoflavones that are the primary health-promoting constituent.
Soy has infiltrated the American diet as an inexpensive meat and dairy alternative, and a nearly ubiquitous cheap commercial food filler, protein fortifier, and oil. My 18-year old daughter, raised vegetarian eating whole, natural foods, with a modest amount of soy on occasion, recently bemoaned that practically all of the foods in her college cafeteria list soy as an ingredient. She’s right – it’s in practically everything.
The good news is that most traditional, organic soy products in the US are made from non-GMO soybeans. The Non-GMO Project is a non-profit organization “committed to preserving and building sources of non-GMO products, educating consumers, and providing verified non-GMO choices.” You can find a list of good quality soy products on their website. Avoid all GMO soy products.
Are There Health Benefits to Eating Soy?
The answer to this, based on extensive review of the scientific and popular literature, is a resounding YES, there are. Here’s a breakdown of some of the major benefits of soy for women:
Breast Cancer Prevention
Studies have shown that Asian women who have consumed traditional soy products since childhood or adolescence, indeed, have significantly lower rates of breast cancer. Some studies on the breast cancer preventing effects of soy have been conflicting. Overall, however, large reviews of studies called meta-analyses show that soy consumption either has a beneficial impact on breast cancer development, or no impact, but it does not pose a risk.
The breast cancer protective effects of soy are primarily attributed to a group of chemical constituents in soybeans known as isoflavones, which in turn belong to a class of chemicals known as phytoestrogens. They are strikingly similar in structure to the estrogens produced by our bodies, but are weaker than human estrogen, competitively bind with estrogen receptor sites in breast tissue, preventing the stronger “endogenous” estrogen from binding – thus possibly blocking them from causing cancerous changes in the tissue.
Treatment and Prevention of Menopausal Symptoms
Studies on the benefits of soy isoflavones on various menopausal related symptoms have shown generally favorable improvements in perceived vasomotor symptoms, particularly hot flashes. Studies on cognitive function have been mixed; some have shown improvement, however, a single study of older women living in Japan, eating a traditional Japanese diet, had worse cognitive function than women eating a western diet; Hawaiian, though conclusive information cannot be gleaned from this singular study.
Prevention of Osteoporosis
Several smaller, and one large study have shown that the soy isoflavones, especially genestein, reduce bone loss, though no studies have been done over a long enough time to look at fracture prevention. Approximately 3 cups of soymilk, 6 oz. of tofu or tempeh, or 3 oz. dry roasted soybeans (edamame) would provide roughly the amount of soy isoflavones used in the studies.
Cholesterol Reduction and Heart Disease Prevention
Soy makes a reliable positive contribution to a heart healthy diet, especially through cholesterol lowering effects. The recommended amount is 25 grams/day of soy. The FDA approves this health claim. Eating soy may also help lower high blood pressure. In general, a plant-based diet, not just soy, can have these benefits, but soy is an easy addition.
Are There Health Risks to Eating Soy?
A number of concerns have been raised in the popular media about the safety of soy, especially about fertility, thyroid function, and nutrient absorption. Any health risks associated with eating traditional soy foods as a modest part of the diet appear extremely minimal. Here’s a quick review:
Breast Cancer Risk: Eating soy in normal dietary amounts does not appear to increase the risk of breast cancer in any populations, in any study. More likely than not, it has some protective effects. But if it worries you, don’t eat it. Remember, many plant-based foods contain similar phytoestrogens.
Fertility: There has been no evidence of decreased fertility in women or men consuming traditional dietary amounts of soy. No feminizing effects have been seen in men consuming normal amounts of soy foods.
Soy and Thyroid Problems: A review of the literature demonstrates that women with normal thyroid function and normal dietary iodine intakes are not at risk for developing thyroid problems. Even eaten up to 3 times/week in pregnancy, it does not affect thyroid function in otherwise healthy women. Make sure you are getting enough iodine in your diet through iodized salt, seaweeds, or your vitamin supplement. If you do have thyroid problems, soy may not be for you. If you are on thyroid medication, your doctor may need to adjust the dose if you supplement with soy foods, as soy can interfere with the medication’s activity.
Soy allergy: Soy is a common food allergen. If you are allergic – or even sensitive (you have digestive or other symptoms after you eat it) — avoid it, or work with your primacy doctor to see if an elimination diet with later re-introduction is a possibility. Organic, non-GMO soy may be less allergenic.
Interference with Nutrient Absorption: Phytic acid is found within the hulls of nuts, seeds, grains, and beans, including soy. It is an indigestible form of phosphorous that can bind to and interfere with mineral absorption. Phytates are reduced somewhat by cooking, and when consumed in normal dietary amounts in those with an adequate nutritional status, should pose no problems with nutrient absorption. Soy has not been shown to interfere with normal growth. Lactobacilli and other organisms in probiotics contain phytase, which help to break down phytates in the intestine.
Is Soy a Necessary Part of a Vegetarian or Vegan Diet?
Soy is absolutely not an essential ingredient in your diet.
If you feel the jury is out on soy safety, feel free to pass the plate. There are many other excellent vegetarian sources of protein and calcium, particularly other beans and legumes, nuts and seeds, and green leafy vegetables that will adequately meet your nutritional needs. The hormonally beneficial plant compounds found in soy are also found in a variety of beans and leafy green vegetables – eat a wide array of these daily for optimal health.
SUMMARY: Soy and Women's Health in a Nutshell
- Eat only organic, non-GMO, traditional soy foods, particularly fermented forms (soy milk may be an exception as a “medical food” for symptom control during the perimenopause), as a small part of an overall healthy, plant-based diet.
- Eat soy, in moderation, as a small part of an overall healthy, plant-based diet. Soy should only be a complement to your diet, not a mainstay. I generally recommend a maximum of 2-3 servings/week. Emphasize other high quality protein sources for healthy variety in your diet.
- Completely avoid “Frankensoy” products.
- If you have thyroid problems, or are on thyroid replacement medication, work with your doctor to monitor your levels if you eat soy regularly (> 1 x/week).
- Make sure to get adequate dietary or supplemental iodine if you eat soy regularly.