Eating soy has been attributed with near-miraculous health benefits like preventing certain cancers, lowering cholesterol, and keeping us safe from osteoporosis.
But the science does not yet fully or conclusively support these claims or others made in the past 15 years (1).
We’ve been wrong about soy.
While studies in those areas show promise, we are far from being able to extract scientific basis for the curative and disease-preventive powers of soy protein or soy isoflavones.
In fact, there is preliminary evidence that consuming soy isoflavones over long periods of time may cause health problems. In an ironic twist, rather than preventing breast cancer, soy may actually encourage the disease in women (1).
Soy’s good for you, but don’t count on it to cure cancer.
But there are some benefits to consuming soy products because of soy’s excellent nutrient content. Until researchers can produce more data on the benefits of soy beyond its obvious nutritious value, it’s best not to count on the cholesterol-lowering, cancer-fighting, and other benefits of soy products at this time.
Here’s why the FDA misled us about soy and heart disease.
Early soy research in the 1990s (2) led FDA officials to mistakenly believe that consuming soy “may reduce the risk of heart disease”. They allowed manufacturers of soy food items to put this claim on their product labels. Thus, the public caught on and now misconceptions about the real benefits of soy perpetuate.
What’s true for lab rats isn’t always true for humans.
Those early findings were based on results from studies performed on animals. In clinical studies, soy did lower the LDL “bad” cholesterol in animals. However, the parallels between animal and human physiology were exaggerated. When scientists performed similar clinical trials on healthy human volunteers, soy had little or no effect on serum cholesterol (3).
Soy is not the only difference between Asian and Western cultures.
Early studies also drew incorrect conclusions about the role of soy in the diet (4). Since soy is consumed in large quantities in Asia, and since that region historically has lower rates of cardiovascular disease, the role of soy was mistakenly attributed for that connection.
In fact, there are so many cultural and dietary differences between Asian and Western countries that scientists now consider the role of soy to have been greatly exaggerated.
Does soy reduce hot flashes?
There have been some preliminary studies that suggested eating soy isoflavone supplements might eliminate or reduce hot flashes in menopausal women.
A meta-analysis of 55 studies showed promising evidence that soy isoflavones do indeed help, but only a little and very slowly (5). The most that will probably happen is a 25% reduction and that will take a little over three months! Even after that long, only about half the effect will be seen.
It requires almost a year for soy isoflavones to reach 80% of their full effect on hot flashes!
Nevertheless, doctors still recommend taking soy isoflavone supplements for reducing hot flashes and for making them less severe (6). They even do so without knowing the long-term effects of consuming soy products.
For now, doctors and nutrition experts agree to disagree about the real impact of soy isoflavones on menopausal hot flashes.
What about the effects of soy on bone loss?
Soy is believed to have a positive effect on the bone loss rates in post-menopausal women. However, results are mixed and more research is needed (7).
What are “soy isoflavones”, anyway?
Isoflavones are plant-derived substances that act a bit like estrogen. Call them “plant estrogens”, or phytoestrogens. It just so happens that soybeans contain very high levels of isoflavones (highest in the human diet), causing excitement in the medical research community over the possibilities of health benefits.
There is a lot of research on soy isoflavones…on animals.
In fact, there’s already a huge body of research on isoflavones but very little of it was conducted on humans. There are many health claims derived from these studies, especially in the areas of breast cancer, prostate cancer, and bone health.
Journalists make a big deal over unimpressive or inconclusive lab results.
There are actually some promising preliminary results. However, as mentioned earlier, few clinical trials with soy isoflavones have actually been done on human subjects (8). When there does happen to be a study using human subjects, much is made about the positive conclusions while the negatives are minimized.
For example, one meta-analysis concluded that soy isoflavones caused a 20% to 26% reduction in hot flashes (9) but news articles citing this study fail to mention that the time periods studied were 6 to 12 months (10).
Here’s why scientists are excited about soy isoflavones.
Soy isoflavones are a sub-set of flavenoids, which are found in lots of fruit, vegetables, and legumes. Plants make them as a defense against environmental stress, disease, and insects (11).
Since soy isoflavones are very similar in chemical structure to human estrogen, researchers seek clinical evidence for health benefits from taking soy supplements.
However, soy isoflavones may act like estrogen in some tissue while blocking estrogen in other types of tissue (11). We know very little about why and how this is. This area of research is currently in its infancy.
The Final Word
Making absolute claims about the health benefits of consuming soy isoflavones at this time is prematurely optimistic. For now, we know that a diet containing a moderate amount of soy products probably won’t hurt you.
Summary: There might be some health benefits but we don’t yet know anything about the long-term effects of including high doses of soy isoflavone supplements in your diet.
All references retrieved 10/29/2015
- National Center for Complementary and Integrative Health. “Soy”. Retrieved from https://nccih.nih.gov/health/soy/ataglance.htm
- Anderson JW, Johnstone BM, Cook-Newell ME. Meta-analysis of the effects of soy protein intake on serum lipids. National Institutes of Health. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/7596371
- JM van Raaij, MB Katan, CE West and JG Hautvast. Influence of diets containing casein, soy isolate, and soy concentrate on serum cholesterol and lipoproteins in middle-aged volunteers. The American Journal of Clinical Nutrition. Retrieved from http://ajcn.nutrition.org/content/35/5/925.abstract?ijkey=ddf60a294968bb5bed025bf6c1147a7c9ff75a8f&keytype2=tf_ipsecsha
- Meinleib, Manning. Seven Countries: A Multivariate Analysis of Death and Coronary Heart Disease. The Journal of the American Medical Association. Retrieved from http://jama.jamanetwork.com/article.aspx?articleid=373603
- Lujin Li, Yinghua Lv, Ling Xu and Quingshan Zheng. Quantitative efficacy of soy isoflavones on menopausal hot flashes. Retrieved from http://onlinelibrary.wiley.com/doi/10.1111/bcp.12533/abstract
- Norton, Amy. Does soy help cool hot flashes after all? Reuters. Retrieved from http://www.reuters.com/article/2012/04/27/us-soy-hot-flashes-idUSBRE83Q11M20120427
- Sacks, F et al. American Heart Association Journals. Soy Protein, Isoflavones, and Cardiovascular Health. Retrieved from http://circ.ahajournals.org/content/113/7/1034.full
- Stanford Medicine Prevention Research Center. The effects of soy isoflavoneson the breast, prostate, and bone. Retrieved from http://nutrition.stanford.edu/projects/soy.html
- Taku, Kyoko et al. Extracted or synthesized soybean isoflavones reduce menopausal hot flash frequency and severity: systematic review and meta-analysis of randomized controlled trials. Retrieved from http://journals.lww.com/menopausejournal/Abstract/2012/07000/Extracted_or_synthesized_soybean_isoflavones.11.aspx
- Daniells, Stephen. Meta-analysis supports soy isoflavones efficacy against hot flashes. Nutra Ingredients-USA. Retrieved from http://www.nutraingredients-usa.com/Research/Meta-analysis-supports-soy-isoflavones-efficacy-against-hot-flashes
- Iowa State University Soybean Extension and Research Program. Soybean Uses. Retrieved from http://extension.agron.iastate.edu/soybean/uses_isoflavones.htm