The Benefits of Soy

Discussion in 'Chit Chat' started by Thunderdog, Feb 20, 2008.

  1. I recently came across an article on WebMD that suggests soy consumption may help prevent male pattern baldness and prostate cancer:

    However, there is no lack of controversy surrounding soy. For every source or study that supports soy consumption for its perceived benefits, there seems to be another that cites adverse effects. For example, there are those who believe that soy consumption leads to gynecomastia (breast enlargement in men), reduced testosterone and libido, as well as an unfavorable effect on lean body mass. Because I am only a layman, I found myself out of my depth amid this controversy. Therefore, I contacted Dr. Joe Schwarcz, Director of McGill University’s Office for Science and Society, which is dedicated to demystifying science for the public, the media and students. Dr. Schwarcz was kind enough to e-mail me an excerpt from his book, An Apple a Day, which touches on soy. Here is that excerpt:

    Soy Protein and Soy Isoflavones

    I never thought I would get excited about tofu. Frankly, the taste doesn’t thrill me. But I am intrigued by some of the scientific studies that have linked eating soy products to protection from disease. Japanese women, for example, have one quarter the breast cancer rate of North Americans. And Japanese women eat a lot of soy products. Of course this does not necessarily mean that soy consumption has anything to do with breast cancer; after all, there is a very strong association between the disease and the wearing of skirts. But of course nobody thinks that the wearing of skirts causes breast cancer. However, it may well be that the soy connection is more than just a chance association. Before exploring the possible benefits of soy, though, let’s remember that breast cancer is a complex disease with many possible contributing factors. It is age-related, has a genetic component and is also linked to excessive alcohol consumption. There may be a connection to high levels of certain fat-soluble pesticides and the types of fat in the diet may also play a role.

    Our soy saga really starts back in the 1940s when Australian farmers noticed that sheep grazing on a certain type of clover failed to reproduce normally. Vetenarians found that the animals’ urine contained high levels of equol, a compound previously found in the urine of pregnant horses. As it turned out, bacteria in the sheep's intestine were capable of converting a naturally occurring compound in clover to equol. And equol was known to have biological activity similar to estrogen! It was no great surprise that an estrogen-like substance should interfere with fertility; after all, estrogen was known to play an important role in human reproduction. Scientists then began to wonder if other plants might also produce compounds with estrogenic activity. Enter the soybean. This Asian staple turned out to be rich in phytoestrogens (plant-derives estrogens), known as “isoflavones.” Genistein and daidzen, in particular, were of interest because they were partially excreted in the urine and could be correlated with the amount of soy in the diet.

    The discovery of phytoestrogens raised eyebrows because scientists already suspected that estrogen and breast cancer were somehow connected. Women exposed to more estrogen over a lifetime were known to have a higher risk of contracting the disease. This includes women who come into puberty early, reach menopause late or have few or no children. In other words, it seems that any factor that lowers the total number of menstrual cycles over a lifetime lowers the risk.

    Now we get back to our Japanese women. They have longer menstrual cycles, averaging 32 days compared with the North American 29 days. This could mean thirty to forty fewer periods in a lifetime. They also have up to a thousand times more phytoestrogens in the urine than North American women. But the soybean plot really thickens when we note that Japanese consume 30 times more soy products than we do, and that Japanese who migrate to North America and take up the North American diet and lifestyle show cancer rates comparable to other Americans.

    We can even postulate a possible mechanism for the isoflavone-breast cancer connection. Some cells in breast tissue are known as estrogen-responsive, meaning that they contain certain proteins (estrogen receptors) to which estrogen can bind, very much in the fashion of a key fitting into a lock. This binding unleashes a sequence of events in the nucleus of the cell which eventually leads to the manufacture of certain proteins that cause cell proliferation. It is such abnormal cell multiplication that leads to cancer. Isoflavones, it seems, are actually "weak estrogens." They fit into estrogen receptors but do not stimulate much cellular activity. At the same time, they prevent estrogen from binding with the receptor. It is as if the wrong key had been inserted into the lock. The key cannot be turned, but it effectively prevents another key from being inserted.

    So much for associations and theory. What practical evidence can we muster to show that soy may actually prevent breast cancer? A number of animal studies have demonstrated that the consumption of soy or isolated isoflavones reduces tumor development. Harvard researchers found that rats fed isoflavones for two weeks before being injected with breast cancer or prostate cancer cells developed far fewer tumors than control rats. Animals that drank tea in addition to the isoflavones did even better. Human data is less direct, but some does exist. Dr. David Jenkins of the University of Toronto examined urine from volunteers on a low fat diet that included 33 grams of soy protein a day. The diet resulted in reduced hormonal activity in the urine as measured by the effect on human breast cancer cell lines. Jenkins suggests this corresponds to a slight protective effect against breast cancer.

    Researchers have also compared groups of breast cancer patients with matched controls and noted a decreased risk of up to 50% in premenopausal women who consumed soy daily. A classic study in Singapore showed that breast cancer rates correlated inversely with the amount of soy protein eaten on a regular basis. More than twenty studies of Asian women have shown that even 1 cup of soy milk or half a cup of tofu a day is associated with reduced cancer risk. In addition, some studies have found that menopausal women who start eating 20 grams of soy protein powder daily, (roughly equivalent to a soy burger, a cup of soy milk or a serving of tofu) show a reduction in the severity of menopausal symptoms. An added benefit is increased bone density in the spine. As far as premenopausal women go, the same kind of diet increases the length of their menstrual cycles by 2.5 days, while the isoflavone content of their urine also rises dramatically. It is certainly apparent that soy has estrogen-like activity!

    Genistein, the main isoflavone, may have yet another effect. It decreases the growth rate of blood vessels that nourish tumors. This inhibition of "angiogenesis" may turn out to be an important anti-cancer effect. It may even explain why men who have high levels of genistein in the urine seem to be protected from prostate cancer. Although the isoflavones appear to be the most interesting anti-cancer compounds in soybeans, there are others. Folic acid, for one, has been shown to prevent mutations in DNA.

    There are, however, some inconsistencies in the soy saga. A study of Japanese women showed that women with breast cancer had consumed no less soy than a control group unaffected by the disease. Chinese women, who eat only about a third of the soy based foods that the Japanese eat have the same low rate of breast cancer. Of course it is possible that a certain amount of soy is protective but eating more carries no further benefit, and may even present a risk. In the test tube, at very low concentrations, genistein enhances human breast cancer cell proliferation while at higher concentrations it inhibits it. The timing of soy consumption may also be important. Female rats, for example, are protected against carcinogen induced breast cancer if soy is given before puberty, but not if given later in life. In humans, isoflavones may act differently after menopause when natural estrogen levels are low, than earlier in life when copious amounts of estrogen are produced.

    Epidemiological studies of Asians do indeed show that it is soy intake early in life that is protective. Later on, at least in theory, when there is less competing natural estrogen, soy may have a different effect.

    Continued on next post.
  2. ...Continued

    After menopause, women produce varying amounts of estrogen and even small such variations may be important. If estrogen levels are low, high doses of soy can have an adverse estrogen-like effect, but soy’s isoflavones can block the adverse effects of natural estrogens if these are present at a high level. This is more than just a theoretical possibility. Charles Wood at Wake Forest University treated postmenopausal monkeys with a high or low dose of estrogen and then fed them diets with varying amounts of isoflavones. Isoflavones had no effect on the low-estrogen animals, suggesting that soy intake after menopause does not increase breast cancer risk. Even more comforting were the results seen in the animals given a high dose of estrogen. When these were put on a diet containing 240 mgs of isoflavones a day, they showed a reduced susceptibility to breast cancer! It is hard to know what to do with this information because that amount of isoflavones is attainable only from supplements, but at least it reduces the concern that phytoestrogens might mimic estrogen when it is not around. Postmenopausal women who want to give soy products or isoflavone supplements a try to reduce menopausal symptoms need not worry about increasing their breast cancer risk. While many studies have come up short, some have shown that a daily intake of about 160 mg of isoflavones can lead to a reduction in hot flashes and night sweats.

    While the available information suggests that soy, particularly if consumed early in life, may protect against breast cancer, it doesn’t shed light on soy’s effects when the disease is already present. There just isn’t enough data to make recommendations in this case, but the prudent approach would be to refrain from going overboard with soy consumption.

    Of course everyone worries about cancer, but heart disease is a bigger killer. And here too there is a lot of talk about soy’s protective effects. Actually, there is more than just talk. By 1999 enough scientific evidence had been gathered by soy product producers to petition the U.S. Food and Drug Administration to allow a “heart healthy” claim on their packages. After reviewing the evidence available at the time, FDA agreed that diets rich in soy protein, as found in tofu and soy milk for example, were capable of reducing blood levels of LDL, the “bad cholesterol.” American products are now allowed to claim that daily consumption of 25 grams of soy protein, coupled with a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. This claim is allowed as long as a serving of the food in question contains at least 6.25 grams of soy protein, less than 3 grams of fat, with no more than 1 gram of the saturated variety and less than 3 milligrams of cholesterol.

    Not everyone was happy with the FDA’s approval of a label claim, including some of the Agency’s own scientists. Detractors maintained that excessive soy consumption can cause goiter, an enlargement of the thyroid gland, visible as a bulge in the neck. Genistein and daidzein, isoflavones found in soy, were said to inhibit thyroid hormone synthesis by inactivating thyroid peroxidase, a vital enzyme. When thyroid hormone levels drop, the pituitary gland secretes more thyroid-stimulating hormone (TSH), causing the thyroid gland to grow and bulge. While there may be some laboratory evidence for the effect of isoflavones on the thyroid, there is no evidence that populations consuming a lot of soy show an increased risk of goiter or any other thyroid disease. Neither is there evidence, as has been suggested, that soy-fed babies show abnormal development. or that high levels of phytoestrogens may cause feminization of boys. Three decades of soy formula use have revealed no correlation between consumption and developmental or hormonal abnormalities.

    A more realistic concern is that the early studies about soy’s benefits have not been corroborated by recent, better trials. Some 22 clinical investigations have been carried since 1999, examining the effect of large amounts of soy protein on cholesterol levels. The results have been unimpressive. Cholestrol was lowered on average by just 3%! Supplements containing isoflavones had no effect on cholesterol, and no clear evidence for cancer prevention has been found. Of course, this doesn’t mean that soy-contaning foods are not healthy choices. They are. But they are not a nutritional panacea. Replacing animal protein with vegetable protein is certainly helpful because it reduces the intake of saturated fats and cholesterol. Furthermore soy contains a specific fatty acid, alpha-linolenic acid, which, as we have already seen, has been linked with a reduction in heart disease, independent of cholesterol lowering. A tofu salad still beats a smoked meat sandwich when it comes to health. But unfortunately not when it comes to taste.


    I followed up with another e-mail to Dr. Schwarcz, and wrote the following:

    Just to put a finer point on it, based on the Wake Forest University study on postmenopausal monkeys, which concluded that isoflavones had no effect on the low-estrogen animals, may I therefore conclude that, insofar as men are concerned, soy does not cause gynecomastia or low libido, and that it does not reduce testosterone levels or adversely affect lean body mass? The results are suggestive, but I would rather get your opinion than draw my own layman conclusions.

    Dr. Schwarcz responded:

    I think you are right in the conclusions you draw. As long as you consider soy as a food and incorporate it in the diet as you would any other food, there is no health issue. It is when people start jumping on some runaway bandwagon and begin to guzzle soy as if it were a drug that trouble crops up.


    And that concludes my post. I would appreciate any input that you folks may have.

    As an aside, As I noted earlier, Joe Schwarcz (PhD McGill 1973) is Director of McGill University’s Office for Science and Society which is dedicated to demystifying science for the public, the media and students.

    His most recent book, An Apple a Day, is subtitled The Myths, Misconceptions and Truths About the Foods We Eat.
  3. fhl


    I drink soy milk almost every day and occasionally eat soy nuts; hoping my breasts don't enlarge.:eek:
  4. My doctor, a naturopath, has warned me not to eat soy or other natural substances that have estrogenic compounds. I already have plenty of endocrine disruptors from plastics and mercury in me.

    My guess is some soy will not be too much, but to use it excessively as therapy to prevent hair loss and cancer might be too much and might not work anyway if a lot of other changes are not made. Preventing illness with one item will not work well.

    Soybeans are a commodity, pushed by food manufacturers, government, soybean growers associations, all looking for market growth. Soy is used in 60% of all refined food products.

    Got soy?

    The most interesting and important thing about soy, is how other cultures have traditionally used soy, fermented soy. The western processing and consumption of soy is far removed from ancient cultures. I doubt if studies on cancer, soy and Asians mention what kind of soy is used.
    The total caloric intake from soy in the Chinese diet is only 1.5%. The amount of soy consumed in Asia averages only 2 teaspoons a day and up to ¼ cup in some parts of Japan. This is certainly not the large amount that we were led to believe.

    The way soy is consumed in Asia is that it is allowed to be fermented first for a long time, from 6 months to 3 years. Only after extensive fermentation is soy being eaten as a condiment

    Studies have shown that 30gram of unfermented soy consumed daily can affect thyroid function and is strongly linked to a host of auto immune diseases such as Hashimoto’s thryoiditis as well as hypothyroidism.

    Modern processed soy products, including soy burgers and soy cheese are not the same as traditional Asian soy. They are by and large unfermented and include tofu and soy protein.
  5. Regarding fermented soy, apparently, some informed people don't necessarily share your view:

    However, I don't think anyone disputes the adverse effects of hydrogenating any oil, soybean or otherwise.

    As for your reference to the total caloric intake from soy in Asian countries, your point is disputed in both the WebMD article I linked in this post, as well as the excerpt of Dr. Schwarcz's book earlier in this thread.
  6. I read the article and it seems as though they can point out many substances contained in soy that would seem to be harmful, but when they look at the statistics of people that consume soy, the problems do not exist. Is that the way you read it?
  7. Good observation.

    I suppose we all have sources that we prefer. I'll go with WebMD, Andrew Weil and Joe Schwarcz, all of whom I referenced in this thread. These are balanced sources that I have come to trust. They don't make sensational claims, one way or the other, and they tend to rely on scientific research and clinical trial results to drawing conclusions of any kind.
  8. That's called the "truly balanced" approach :D