The American Journal of Epidemiology has published a paper that ties soy intake to a 36 percent reduction of hip fractures in a study involving 63,000 people.
Archive for the ‘Soy’ Category
Soy Beans For Bone Health
Thursday, October 29th, 2009AICR: Men Don’t Need to Fear Soy Foods
Monday, September 7th, 2009From the American Institute for Cancer Research:
Nutrition Notes Week of August 24, 2009
Men Don’t Need to Fear Soy Foods
Karen Collins, MS, RD, CDN
It’s no wonder that men who have read the recent stories circulating about soy are confused. Some stories claim that soy foods, such as tofu and soy milk, can lead to breast growth or reduce testosterone levels. Other stories tout the benefits of soy, suggesting soy may help protect against prostate cancer. Women have wondered for years whether phytoestrogens affect their health, from menopausal hot flashes to breast cancer. Now men are left to wonder about soy foods possible unwanted effects.
Soy contains compounds called isoflavones that are known as phytoestrogens, which are weak plant versions of the hormone estrogen. Fears that the amount of phytoestrogens in moderate amounts of soy foods could stimulate men’s breast tissue or reduce their testosterone are not based on sound research. A study of children fed soy protein formula for more than six months showed no hormonal effects. A study of men in their 50s and 60s found that the men who ate soy foods twice a day for three months showed no change in testosterone levels, but had a 14 percent drop in levels of PSA (an indicator of prostate growth used in screening for prostate cancer).
Concerns about lowering sperm count and affecting fertility also do not seem to hold up in human studies of realistic dietary consumption.
Whether or not soy foods offer protection from prostate cancer is still an open question. One recent analysis that combined results from many studies found that men who consumed the most soy foods or the isoflavones they contain were 26 percent less likely to develop prostate cancer. Yet studies overall suggest that men may differ in their response to soy.
Asian populations tend to show a much greater drop in prostate cancer risk with soy foods than Western populations. Japanese men with highest consumption of soy or blood levels of isoflavones have shown 40 to 60 percent lower risk of prostate cancer than those with lowest consumption or blood levels. Yet European studies on the effect of soy are inconsistent.
The difference between Asian and Western populations could stem from several sources, such as the bacteria in our gut. All people carry millions of useful bacteria in our digestive tract that help metabolize food, yet different populations (and people) carry varied types of bacteria. Some bacteria break down food isoflavones into a compound (equol) that is linked with lower prostate cancer risk. Overall, Asian populations show a higher proportion of equol-producers, which could be one reason why soy is more often linked with prostate protection in these groups.
The type of soy food also makes the research challenging. Fermentation may change how easily our bodies absorb isoflavones, which means that fermented soy foods (miso, tempeh, natto) may have a different effect on prostate cancer risk than non-fermented soy foods (soy milk, tofu and edamame). Some studies suggest that the effect of soy foods may depend on its interaction with other food compounds; the lycopene from tomatoes is one such interaction under study.
While we wait for more answers about the possible protection from soy, men can feel safe eating one or two servings of soy foods daily. Soy foods are nutritious, low in saturated fat, and men have consumed them for generations without harm. However, until we know more about isoflavone safety, research does not show benefit or safety of consuming large amounts of isoflavone supplements in hopes of achieving protection.
Karen Collins, MS, RD, CDN, was an instructor at Cornell University and has been involved with the American Institute for Cancer Research for more than 15 years as a writer, nutrition education consultant and public speaker.
Dr. Weil On Soy
Monday, September 7th, 2009
I’ve read several of Dr. Andrew Weil’s books. I don’t agree with everything he has to say, but I like to read his opinions as they seem less biased. Dr. Andrew Weil is a medical doctor (M.D.) and popular health writer with an interest in alternative medicine. Dr. Weil is just as likely to endorse a conventional medical treatment as give a positive ( or negative ) review of an alternative treatment.
Here is what he has to say in an article about eating foods made from soy beans:
I’m aware of Internet paranoia on the subject of soy and the contention that only fermented soy is safe to consume. That is simply not true. Some of the best forms of soy – edamame, tofu and soy nuts – are unfermented and are much more likely to help you than hurt you.
Claims that unfermented soy foods (such as tofu and soy milk) contain toxins that block the action of enzymes needed to digest protein, and that these toxins cause pancreatic enlargement, cancer and stunted growth in animals are misleading. While soy does contain substances (trypsin inhibitors) that may adversely affect the pancreas in animals, there’s no solid evidence that they cause similar problems in humans. Furthermore, trypsin inhibitors are found in all of the vegetables of the cabbage family as well as in beans other than soy.
Other concerns about soy safety focus on the following issues:
- Breast cancer: Here, the idea is that high levels of isoflavones, active ingredients in soy that behave like estrogen in the body, may increase the risk of breast cancer. While high levels of isolated isoflavones may do so, it appears that the total mix of weak plant estrogens in soy protects the body’s estrogen receptors. This protection may reduce the effects of excess estrogen exposure from such external sources as meats and dairy products from hormone-treated cows as well as artificial chemicals and industrial pollutants that act as foreign estrogens. Japanese women whose diets contain a lot of soy foods have only one-fifth the rate of breast cancer that occurs among Western women.
- Thyroid Problems: Excess consumption of soy can affect thyroid function, but only if you have a thyroid disorder to begin with or if you’re not getting enough iodine in your diet (a rare deficiency in the United States). If you take medication for hypothyroidism (low thyroid), and are concerned about the effect of eating two daily servings of soy, have your thyroid levels checked regularly.
- Mineral absorption: The idea that substances in soy called phytates block absorption of essential minerals is also in circulation, but there is no scientific data suggesting that soy consumption leads to mineral deficiency in humans.
All told, based on the evidence to date, I see no reason to worry about eating soy foods, whether fermented or not. I still recommend consuming one to two servings of soy per day, an amount equivalent to one cup of soy milk, or one half cup of tofu, soy protein (tempeh) or soy nuts.
Andrew Weil, M.D.