Coming to the Defense of Scientific Studies

Why you can’t trust everything you read

Kaayla Daniel recently blogged about how the soy industry was going to utilize September’s designation as National Prostate Cancer Awareness Month to promote soy, “tying on light blue ribbons and shilling soy milk, soy powders and soy nuts as the ticket to manly health.”

Actually, September is also National Cholesterol Education Month, a time we chose to celebrate the strong evidence-based heart-health benefits and the FDA health claim, but we want to take a moment to correct some unscientific and factually inaccurate statements of Kaayla Daniel in this blog.

In her “Naughty Nutritionist” blog post, Kaayla Daniel references a July 2013 study by Dr. Maarten Bosland of the University of Illinois at Chicago published by Journal of the American Medical Association (JAMA), Effect of soy protein isolate supplementation on biochemical recurrence of prostate cancer after radical prostatectomy: a randomized trial, as proof soy does not help men with prostate cancer.  The significance of the results of this study have been questioned by several scientists, including Derek Raghavan, MD, of Carolinas Healthcare System in Charlotte, N.C.  Experts at the American Cancer Society say that despite the findings, soyfoods and fatty, omega-3-rich fish are still good, healthy alternatives to red meat.

Dr. Bosland’s study utilized a supplement with 20 grams of soy protein isolate, and not soyfoods, to medically treat men who had prostate cancer and who had had a radical prostatectomy.  This study does not examine the potential for soyfoods to lower elevated PSAs, a current biomarker for prostate cancer, in otherwise healthy men or men with prostate tumors.

Numerous studies have fed isoflavone-rich soy products to men with elevated PSAs and have reported decreases in serum PSA concentration, [i] a slowing in the rise of PSAs,[ii] or no effect on PSAs but also no metastasis of prostate cancer.[iii],[iv] Some research suggests, however, the whole soyfood rather than the isoflavone is responsible for the benefits for men with prostate cancer.[v],[vi] But in none of these interventions with soy isoflavones in men have resulted in abnormal levels of testosterone.

Kaayla Daniel also notes that the effect of soy may be dependent on production of equol, which she says the soy industry avoids talking about. It’s not that we don’t mention it, we do, unfortunately too few researchers measure the levels of equol, a metabolite of the soy isoflavone daidzein that only some people are able to produce in their intestines. Information on equol is simply not there yet, and Daniel herself references two studies that indicate additional research needs to be done to examine the dietary patterns, gut bacteria, and genetic profiles of equol producers, and investigations into whether it is possible to convert equol non-producers to producers. Since those studies, Tanaka[vii] found that soy isoflavone supplements converted some equol non-producers to producers.

Though it is a study from 1998, the most significant research in terms of greatest sample size is a study published in The Journal of the National Cancer Institute that shows prostate mortality rates in 42 countries saw significantly lower prostate cancer death rates with soy consumption. A growing body of more recent research based on soyfood consumption (such as this 2009 meta-analysis) suggests that regular consumption of soyfoods may reduce the risk of prostate cancer by as much as 30%, depending on the type and quantity of soyfoods consumed.

Daniel uses her blog to cite animal research to raise fears about toxicity, carcinogenicity, and brain damage, but more-recent, well-designed research in humans — not animals — does not confirm these findings.  Though rats provide the early basis for hypotheses about substances and disease, human research often finds quite different results and provides the relevant research for dietary recommendations and clinical treatments.

Daniel Doerge, PhD, and Hebron C. Chang, PhD, of the FDA’s National Laboratory for Toxicological Research conduct rat studies testing the toxicity of soy by intentionally feeding extremely high doses to determine maximum safe levels of substances; but these rat studies cannot be used to describe hazards to humans who consume soy isoflavones at much, much lower levels found in foods and regular diets.

The past 15 years have resulted in hundreds of human trials funded by the National Institutes of Health that have led to clearer understanding when soyfoods or soy protein may have beneficial effects and when they do not.  These studies have given reason to include soyfoods in the 2010 USDA and DHHS Dietary Guidelines and the USDA MyPlate Food Guidance.

Finally, Daniel raises concerns from a 2003 study of the impact of a low fat diet with soy supplement on prostate cancer.  In 2010, Dr. Aranson[viii] and others repeated this research with 18 men with prostate cancer who were highly compliant with the diet interventions and found a low fat (15% kcal), high fiber, diet with 35 gm of soy protein supplemented resulted in decreased growth of LNCaP cells from human prostate adenocarcinoma cells compared to a Western (40% kcal fat) diet with no added soy.  Unlike the 2003 study, Tanaka found no significant changes between groups in serum prostate specific antigen, sex hormones, insulin, insulin-like growth factor I and II, and insulin-like growth factor binding proteins.

Beyond the potential for prostate health, there are more reasons for men to choose soyfoods as part of a healthy lifestyle.

 

References

[i] Ide H, Tokiwa S, Sakamaki K, Nishio K, Isotani S, Muto S, Hama T, Masuda H, Horie S. Combined inhibitory effects of soy isoflavones and curcumin on the production of prostate-specific antigen. Prostate. 2010 Jul 1;70(10):1127-33.

[iii] deVere White RW, Tsodikov A, Stapp EC, Soares SE, Fujii H, Hackman RM. Effects of a high dose, aglycone-rich soy extract on prostate-specific antigen and serum isoflavone concentrations in men with localized prostate cancer. Nutr Cancer. 2010;62(8):1036-43.

[iv] Hamilton-Reeves JM, Rebello SA, Thomas W, Kurzer MS, Slaton JW. Effects of soy protein isolate consumption on prostate cancer biomarkers in men with HGPIN, ASAP, and low-grade prostate cancer. Nutr Cancer 2008;60:7-13.

[v] Hsu A, Bray TM, Helferich WG, Doerge DR, Ho E. Differential effects of whole soy extract and soy isoflavones on apoptosis in prostate cancer cells. Exp Biol Med (Maywood). 2010 Jan;235(1):90-7

[vi] Park S, Murphy SP, Wilkens LR, Henderson BE, Kolonel LN. Legume and isoflavone intake and prostate cancer risk: The Multiethnic Cohort Study. Int J Cancer 2008;123:927-932.

[vii] Tanaka M, Fujimoto K, Chihara Y, Torimoto K, Yoneda T, Tanaka N, Hirayama A, Miyanaga N, Akaza H, Hirao Y. Isoflavone supplements stimulated the production of serum equol and decreased the serum dihydrotestosterone levels in healthy male volunteers. Prostate Cancer and Prot Dis 2009; 2009;12(3):247-52.

[viii] Aronson WJ, Barnard RJ, Freedland SJ, Henning S, Elashoff D, Jardack PM, Cohen P, Heber D, Kobayashi N.

Growth inhibitory effect of low fat diet on prostate cancer cells: results of a prospective, randomized dietary intervention trial in men with prostate cancer. J Urol. 2010 Jan;183(1):345-50.

 

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