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Some say that Soy is good for me, while other say it is overrated, or even bad. What’s the scoop?
Nutritional scientists have been studying soy for many years and there is a wealth of data available that based on individual interpretation can provide for a difference of opinion on how beneficial soy is for promoting good health. The general consensus of the vast majority of scientists is that soy is very good for us. My answer will discuss why most scientists believe soy is good and why some scientists are not sure. It is harder to explain why some people think soy is bad for you but I will try.
Let’s start by understanding the areas where there is almost universal agreement and then move to the areas of conflicting opinions. Soybeans are a unique protein source. Unlike most plant proteins, soy contains all nine essential amino acids. Meat also provides all nine essential amino acids. The difference is that soy contains no saturated fat and no cholesterol. The result is that soy is also very low in calories. Red meat is relatively high in saturated fat, cholesterol, and calories. When epidemiological correlations between reduced meat consumption and lower rates of cancer and heart disease became known the interest in soy soared. We know for a fact that in countries like China, Korea, and Japan people eat between 25 – 47 grams of soy daily. These countries have relatively low rates of heart disease, osteoporosis, diabetes, and breast, colon, and prostate cancers. The question was why was this happening? What researchers found was that soy had other unique properties.
Soybeans are uniquely rich in phytoestrogens called isoflavones. The reality is that if you don’t eat soy you don’t have isoflavones in your body. Much of the controversy about soy comes from what we know about isoflavones. Soy also contains saponins, they are less controversial, but again cause some individuals concern.
Phytoestrogens are plant molecules structurally similar to estrogen. The strongest of the phytoestrogens are the isoflavones. The most important of the isoflavones are genistein and daidzein. Soy contains both. Everyone agrees that isoflavones are much much weaker than the estrogen produced by a woman’s ovaries. It is also generally accepted that you find only a small amount of isoflavones per serving of soy. Still, the question remains - are these isoflavones what accounts for the good news about soy or do they blemish soy’s nutritional value?
The science about isoflavones appears clear if you accept the fact that while isoflavones structure is similar to estrogen, the body’s reaction to them is different. The body’s response to isoflavones is simply not the same as it is with estrogen. Soy isoflavones do ease menopausal symptoms by providing the body an alternative molecule. They also improve bone health by a similar mechanism. The good news is that the science shows that isoflavones compete with the body’s own estrogen receptor sites. This protects the body against hormone-related disorders not exposing it to excess estrogen.
We know that isoflavones are also powerful antioxidants. There is compelling evidence that the low cholesterol content of soy and the antioxidant properties of isoflavones reduce heart disease. The American Heart Association recommends soy protein as a way to reduce cholesterol levels. There is evidence that soy isoflavones inhibit the growth of the cells that form plaques providing another heart protective mechanism. There is also a significant amount of evidence that isoflavones protect against hormone dependent cancers like breast and prostate cancer as I previously explained.
The other active molecules found in soy are saponins. Soy saponins resemble cholesterol in structure and are thought to lower cholesterol by enhancing excretion or by blocking absorption or both. Saponins also have antioxidant properties and therefore protect DNA and cell walls from damage.
The scientists that have concerns about soy cannot accept the fact that an estrogen-like molecule and a cholesterol-like molecule found in soy can actually be good for you. They believe that isoflavones cause hormonal imbalances. There is a long-standing belief that soy causes hypothyroidism in women. Three recent studies confirmed that soy did not harm thyroid function but that is not good enough. There is the belief that the body treats isoflavones the same as estrogen. The science contradicts this but they want more research.
The people who want you to believe that soy is actually bad for you make statements like this. They are quick to point out that since the early 1900’s the greatest amount of soybeans grown in the United States is for livestock feed. They have made the conclusion that soy is for animals not for people. What they don’t add is that the balance of the American soybean crop is sent to Japan, China, and Korea. At the present time, the United States breast cancer rate is four-fold that of Japan, five-fold that of China, and ten-fold that of Korea. There are comparable results with prostate cancer.
Several large medical organizations have concluded that soy protein is safe. Cardiologists, cancer specialists, and women’s health specialists regularly recommend soy products to their patients.
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