The Story of Soy

Edamame, or soybeans, Japanese style with salt, by Framboise, via flickr

By Kate Prengaman

Soy has become both famous as a health food and infamous as a health risk after it’s introduction to the western world as an alternative protein. Health claims include that soy protein products can help lower your cholesterol and prevent cancer. Soy supplements have been touted for menopausal women as estrogen supplement. On the other hand, that same estrogen in soy has been considered a serious risk, potentially making our children gay! (Just kidding, this claim has no scientific merit)  But what does the science really say about soy consumption and our health? 

The health benefits of soy began when researchers noticed that Asian populations have lower risks of heart disease and hormonal cancers. Since soy protein is traditionally a significant part of the diet, scientists began to study the impact of soy on the diet. The US Food and Drug Administration stated in 1999 that “daily consumption of soy is effective in reducing the risk of coronary heart disease” and soy products started selling rapidly.

From 1996 to 2009, according to the Soy Foods Association of North America, soy food sales have “increased from $1 billion to $4.5 billion.” In 2009, Soy milk accounts for just under a quarter of the market, and the other category, which includes baked goods, cereals, pasta, powdered nutritional supplements, and snack foods, is the leader with about 35 percent. Tofu and soy cheese and deserts come in between 4-5 percent. Meat alternatives and energy bars account for the remain, coming in at 14 and 18 percent of soy sales. From 2000-2007, more than 2,700 new food products were introduced with soy a an ingredient. In 2010, 85 percent of US consumers reported that they perceive soy foods as healthy, and 31 percent seek out products containing soy for health benefits.

The most controversial component of soy products are the phytoestrogens that soy contains.  Soy and flax have particularly high levels these compounds, which includes flavaniods and isoflavens. The amount of phytoestrogen varies widely in soy foods: soybeans have three times a much phytoestrogen as tofu, and 33 times as much soy milk, for 100 grams of each food.  Now that enough conflicting, controversial studies have been run on soy consumption, scientists can run meta-analysis projects that seek to really understand how soy affects our health.  Here’s the basic conclusion for breast cancer risk, reducing cardiovascular disease, and the risks of soy infant formula

Phytoestrogens and Cancer:

Moderate levels of phytoestrogen in the diet may be linked to lower rates of breast and endometrial cancer, according to population studies comparing Asian women with significant amount of soy food in the diet with American women on a low soy, western diet.  However, extremely high doses of phytoestrogens are linked to higher rates of breast and uterine cancers, so it’s all a matter of dose.  Soy supplements marketing as natural menopause treatments, which have very high doses of the phytoestrogens, may be detrimental to a women’s risk of breast cancer, while a balanced diet that includes tofu, edamame, or veggie burgers regularly is not.   For women receiving treatment for breast cancer, doctors will recommend a reduction in soy consumption because of indications that the phytoestrogens may disrupt the effects of certain anti-tumor drugs and interfere with hormone treatment.

To sort through all of the studies done linking soy consumption to decreased and increased risks for breast cancer, the NIH did a meta-analysis in 2006, looking at the results of 18 different studies, from 1974 through 2004. They found a significant statistical association showing soy intake may be related to a small reduction in breast cancer risk, but it’s very small.

Although isolated soy isoflavone has been used in high concentration supplements of menopause symptoms, like hot flashes, meta-analysis found no significant effect of soy on the symptoms. They do not recommend soy isoflavone supplements, in food or pills, because in the meta-analysis, they do not see significant health benefits from clinical use. Many of the studies that initially suggested positive effects were only documenting placebo effects. These “natural” products continue to sell, and the myth that soy phytoestrogens are a safe and effective treatment for menopause symptoms remains quite popular, despite scientific evidence to the contrary.

Soy products and heart disease:

The connection between cardiovascular health and soy in the diet was presented to most Americans by the  FDA in 1999. Today, the NIH currently recommends “25 grams per day of soy protein may reduce the risk of heart disease”.  But the initial research has come under scrutiny. In 2006, the American Heart Association stated that “Earlier research indicating that soy protein as compared with other proteins has clinically important favorable effects on low density lipoprotein (LDL) cholesterol and other cardiovascular disease risk factors has not been confirmed by many studies reported during the past 10 years”

Soy Milk, by theimplusivebuy, via flickr

In 2006, a meta-analysis of 22 trials found that in the majority, consumption of isolated soy proteins with isoflavone decreased LDL cholesterol concentration approximately 3 percent, when compared to milk or other proteins. However, the authors of the report explain that “this reduction is very small relative to the large amount of soy protein tested in these studies, averaging 50 g, about half the usual total daily protein intake” They saw no significant effects on HDL cholesterol, blood pressure, or other heart disease risk factors.  In the 19 studies that employed soy isoflavones “the average effect on LDL cholesterol and other lipid risk factors was nil.”

In 2007, the FDA issued an announcement that it would undertake a re-evaluation of it’s statement about soy’s effects on reducing coronary heart disease, because of the conflicting data from scientific studies. No results have been published yet.

Soy Infant Formula: The Actual Concern

Soy is increasing in use in infant formula worldwide. Approximately 25% of infants in the US, about 1 million a year, use mostly soy formula. Parents choose soy formula because of perceived health benefits, their vegetarian diet, or concerns about milk allergies.

According to Patisaul and Jefferson’s 2010 review article,  “Infants on soy formula consume approximately 6–9 mg isoflavones per kg body weight per day, an amount, when adjusted for body weight, that is up to seven times higher than for adults meeting the FDA soy consumption guideline, or Asians consuming a traditional soy-based diet.” Infants on soy diets have circulating phytoestrogen levels 13,000-22,000 times higher than infants who are breast-fed, and 50-100 times higher than the estradiol level in preganant women. These blood levels are high enough to produce many of the physiological effects described in recent studies.

BPA-free Baby Bottles, by Alicia Voorhies, via flickr

Consumers freaked out about the BPA, a endocrine disruptor in the plastics of baby bottles, and demanded replacements, but they neglected to consider the endocrine levels of the phytoestrogens in the infant formula, which are an order on magnitude higher than the BPA.

Researchers recommend more studies on the long term effects of soy infant formula as a “public health imperative.” In the UK, Australia, and New Zealand all caution against over-use of soy infant formula. In some countries it is by prescription only for children who cannot tolerate milk.  In the US, the American Academy of Pediatrics announced that soy infant formula has no advantage over cow’s milk, but it did not recommend against it’s use. There are few long term studies on soy infant formula’s effect on future health, but initial surveys have shown longer menstrual cycles and increased menstrual discomfort for teenage girls who had been on soy based formula as infants.

In conclusion, soy is not a miracle health food that can save us from heart disease of cancer.  It can be part of a low cholesterol diet as a protein source. Eating 25 grams a day have not been linked to any deleterious effects. Soy phytoestrogen supplements for menopause therapy don’t do any good, and may do more harm. Eating soy does not contribute to breast cancer risk, but if you are being treated for cancer, it may interfere with your drugs, and you should cut soy from your diet. Too many questions remain about infant formula, but it might have long term effects on reproductive health.


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