More Studies

SOY AND MENOPAUSE

Five recent studies have shown that soy is worthless in treating symptoms of menopause. A study carried out at Monash University, Clayton, Australia found that three months of soy supplements providing 188 mg of isoflavones daily did not improve menopausal complaints in 94 older postmenopausal women compared with those taking a placebo (Climacteric 2000 Sep;3(3):153-4). Investigators at the Department of Food Science and Human Nutrition at Iowa State University examined changes in menopausal symptoms in response to 24 weeks of isoflavone-rich diets, comparing women receiving about 80 of mg isoflavones per day with a group receiving 4 mg per day and a group receiving none. They found no treatment effect on frequency, duration or severity of hot flashes or night sweats. As in the Australian study, all groups reported a decline in overall symptoms, indicating either a placebo effect or simply an improvement in symptoms during the study (Menopause 2001 Jan-Feb;8(1):17-26). A study carried out by the University of Milan came to the same conclusion. Patients were administered 72 mg per day of soy-derived isoflavones or placebo under double-blind conditions. Both groups recorded a 40 percent reduction in the number of hot flashes (Fertil Steril 2003 May;79(5):1112-1117). In a similar study carried out at the University of Pittsburgh, those women taking the placebo actually showed improvement! Hot flashes, night sweats and vaginal dryness improved from baseline in the placebo group but not in the soy group. In addition, insomnia was more frequent over the 6-month study in the soy group (J Soc Gynecol Investig 2002 Jul-Aug;9(4):184-5). And, finally, a study carried out in Helsinki University Central Hospital found no difference between phytoestrogens and a placebo for treating menopausal symptoms in breast cancer survivors (Obstetrics and Gynecology 2003;101:1213-1220).

In a review published in late 2002, soy apologist Mark Messina argues that soy is better than hormone replacement therapy because soy "seems unlikely to increase risk because it has no progestin activity." He notes that there is no evidence to suggest that soy will increase the incidence of clots or stroke but "only limited data are available in this area." Ditto for heart disease, osteoporosis and colon cancer--soy may help but the evidence is scanty. ". . . [T]he evidence warrants recommendations that menopausal women include soy in their diets," he says. Not a word about the growing number of studies showing that soy offers no benefit at all for menopausal problems. Symptoms typically improve on their own. Why not just take the placebo--at least it won't depress thyroid function or upset the delicate chemistry of breast tissue.

MORE WRONG CONCLUSIONS

In our last issue (Spring 2003), we listed several studies in which the authors came to positive conclusions when the study actually showed negative effects. A study carried out at University Hospital of Wales can be added to the list. Male volunteers ate three scones per day in addition to their normal diet for a period of six weeks. The scones were made either with wheat flour or soy flour providing 120 mg per day of isoflavones (about the amount contained in 3 cups of soy milk). Testosterone levels fell in the volunteers eating the soy but researchers did not stress this alarming finding in their conclusion. Instead, they noted "significant improvements in two of the three markers of oxidative stress" and concluded that "these findings provide a putative mechanism by which soya supplements could protect against prostatic disease and atherosclerosis (Eur J Clin Nutr 2003 Jan;57(1):100-6).

SOY AND THYROID FUNCTION

Although soy has been known to suppress thyroid function for over 60 years, and although scientists have identified the goitrogenic component of soy as the so-called beneficial isoflavones, the industry insists that soy depresses thyroid function only in the absence of iodine. The University of Alabama at Birmingham reports a case in which consumption of a soy protein dietary supplement decreased the absorption of thyroxine. The patient had undergone thyroid surgery and needed to take thyroid hormone. Higher oral doses of thyroid hormone were needed when she consumed soy--she presumably used iodized salt so iodine intake did not prevent the goitrogenic effects of soy (Endocr Pract 2001 May-Jun;7(3):193-4).

SOY AND ENDOCRINE DISRUPTION

Scientists at the National Institute of Environmental Health Sciences in North Carolina treated newly born mice with the soy phytoestrogen genistein for the first five days after birth. They found that significant alterations occurred in the ovaries. Their conclusion: "Given that human infants are exposed to high levels of genistein in soy-based foods, this study indicates that the effects of such exposure on the developing reproductive tract warrant further investigation" (Biol Reprod 2002 Oct;67(4):1285-96).

SOY INCREASES ANXIETY AND STRESS

A new report on a fascinating isoflavone study begins with the following statement: "Isoflavones form one of the main classes of phytoestrogens and have been found to exert both oestrogenic and anti-oestrogenic effects on the central nervous system. The effects have not been limited to reproductive behaviour, but include effects on learning and anxiety and actions on the hypothalamo-pituitary axis." Noting that most rat chow contains soy, investigators compared the behavior of rats given isoflavones in their diets with those on an isoflavone-free diet. Rats fed isoflavones spent significantly less time in active social interaction and had significantly elevated stress-induced corticosterone concentrations. The conclusion: "Major changes in behavioural measures of anxiety and in stress hormones can result from the soya isoflavone content of rat diet. These changes are as striking as those seen following drug administration and could form an important source of variation between laboratories" (Psychopharmacology (Berl) 2003 Mar 5).

WHITEWASH

With researchers continuing to find reasons to avoid soy--thyroid problems, endocrine disruption, reduced tolerance for stress and a variety of pathologies in animals exposed to soy in utero and during growth--the cautionary principle calls for warning labels on soy foods designed to be consumed in all but minimal amounts. Instead a review of studies headed by Ian C. Monro comes to the following conclusion: "Whereas results in some studies are limited or conflicting, when viewed in its entirety, the current literature supports the safety of isoflavones as typically consumed in diets based on soy or containing soy products [emphasis ours]." "The current literature" means those studies the group chose to include in its review. Many were of very short duration and described in a way that glossed over negative findings. The review was funded by a grant from the United Soybean Board.

Sidebars

LISTING OF STUDIES SHOWING
ADVERSE EFFECTS OF SOY

As part of our ongoing efforts to keep the public up-to-date on the problems with modern soy foods, we have compiled two lists of studies showing adverse effects of soy: one lists studies showing the toxicity of soy isoflavones (estrogen-like compounds in soy) and the other lists studies showing problems with consumption of soy foods in general. We looked only at studies published in scientific journals--the total was over 150! Very often, the conclusions posted in the abstracts of these studies glossed over negative findings, or even presented these findings as beneficial. Most interesting to us was the large number of recent studies showing carcinogenic and mutagenic effects of soy isoflavones. (We have been accused of citing only older studies and ignoring more recent "positive" findings.) These two lists were submitted to the COT in the UK, and the USDA in the US.

This page was posted on 12/13/03