Solving the soy debate: the latest research

I recently wrote this article as part of a freelance assignment. The publisher decided not to use it, so I will share it with you instead!

For many years, soy has been a controversial topic. Conflicting research over the last decade has left consumers confused and wary. This, along with the abundance of information (and misinformation) on the Internet, has led many consumers to avoid soy completely out of fear of developing cancer or consuming GMOs (Genetically Modified Organisms). This article will examine the latest research and provide updated recommendations for soy consumption.

Characteristics of Soy

Soy products are found in many forms in the United States food market, most commonly tofu, tempeh, soy milk, and edamame. There is also an abundance of processed soy products, such as vegetarian forms of chicken nuggets, burgers, and hot dogs. Soy is a rich source of many dietary nutrients, including protein, fiber, vitamin K, and B vitamins.




Soy and Cancer Prevention

Many studies have shown the protective effects of soy against cancer. It should be noted that in many Asian countries, where soy consumption is high, overall cancer rates are much lower than in the United States. One cohort study in Japan showed that consumption of isoflavones was associated with a reduced breast cancer risk (Journal of National Cancer Research, 2003). Genistein, an isoflavone in soy, is thought to prevent cancer cell growth by binding estrogen to decrease the development of hormonal cancers, particularly that of the breast. This contradicts older studies that showed a link to increased cancer, however these studies were conducted on mice. The author of one such study, Dr. Mark Messina, later discovered that rodents metabolize isoflavones at a much higher rate than humans, and therefore the effects were only seen in very high doses. In fact, even the rodent studies did not consistently produce these results (American Journal of Clinical Nutrition, 2011). Studies have been difficult to conduct in the United States, because soy intake is relatively low among American women (Today’s Dietitian, 2013). Therefore, it is challenging to determine the exact reason(s) that Asian women have lower cancer rates.

One proposed theory to explain the disparity between US and Asian cancer rates is the amount of meat in the diet. Typically, the Japanese diet contains almost no saturated fat due to relatively low meat consumption. Countries with higher animal fat intake have higher breast cancer rates. Even in modern Japan, where a Western diet is more commonly consumed than in past decades due to the rise of international fast food chains, breast cancer rates are rising among the younger generations. Meat and other foods high in saturated fat are known to increase estrogen production. However, saturated fat is not thought to be the direct cause, as many studies have shown positive relationships between meat intake and breast cancer even when fat intake is controlled (Physicians Committee for Responsible Medicine, 2016).

Soy and Cancer Survivors

One common perception is that women who have survived breast cancer should avoid soy products. The thought process behind this is that because soy foods promote estrogen production, that the estrogen can promote the growth of breast cancer cells. Current research, however, contradicts this belief. The largest study to date, a pooled analysis of studies consisting of over 10,000 breast cancer patients, showed that consuming as little as 10 mg of isoflavones was linked to a 25% decrease in recurrence. This was true in both American and Asian women. Isoflavones have also not been shown to have any harmful interaction with hormone treatments like tamoxifen, and in fact may even be protective of women taking these treatments. However, more research is needed in this area to make conclusive recommendations (Today’s Dietitian, 2013).

Areas of Controversy

Soy has been purported to reduce the risk of heart disease by lowering LDL cholesterol. These findings are controversial as it is unclear whether it is a direct result of eating soy or simply due to replacing animal proteins with soy protein. In addition, benefit was only shown by consuming at least 50 grams of soy protein daily, the equivalent of eight cups of soymilk. Consuming soy in these quantities is likely to be difficult to achieve for most individuals (The Nutrition Source, 2014).

Another area of current research is the impact of soy consumption on memory. One study of Hawaiian women of Japanese heritage showed that excessive soy intake was possibly related to a decline in cognitive function, but this finding has not been confirmed by other long-term studies (The Nutrition Sources, 2014).

Finally, there is ongoing debate regarding the effects of consuming GMOs. Unfortunately, soy is one of the most common GMO crops grown in the United States. The long-term effects of eating GMO foods are not yet known, as not enough time has elapsed since their adoption into the United States food supply. It is currently the consensus of the USDA and FDA that GMO crops have no adverse health effects, but one must consider the well-known relationships that exist between the government and agricultural giant Monsanto, the largest producer of GMO seed in this country (Robin, 2008). There is no current law requiring labeling of GMO foods, however many companies are doing this voluntarily. Many manufacturers of soy products, such as Silk, are proudly labeling their products as non GMO.

Whole vs Processed Soy

One issue that many individuals have with soy is that fact that it is often highly processed in the United States. Great effort has been made by manufacturers to lure meat-eating consumers by creating products that have a similar taste and texture to meat. As with the processing of all other foods, the chemical composition and nutritional content is changed, and arguably, so are the health effects. Isoflavone content and antioxidant potential can be lost through various steps in processing such as bleaching, isolating, and deodorizing (South Dakota State University, 2008). There is sweeping evidence that consuming a diet high in processed foods, particularly processed meat, can lead to adverse health effects.

Current Recommendations

Soy should be chosen in its whole, unprocessed form, such as edamame, and it is generally recommended that a whole-foods diet be adhered to as much as possible (Today’s Dietitian, 2013). When purchasing soy foods, look for the non GMO label on the package. The Dietary Guidelines for Americans currently recommends 1-3 servings daily of soy foods to get the benefits of the isoflavones (USDA, 2015).