Just how safe is soy? Are the fears justified?
We’ll answer very simply: soy is an excellent food to include in one’s diet.
The good news is that not only is soy safe when properly processed, it’s actually beneficial when used in moderation—meaning you should get a good variety of nutrients by varying your diet. Soy is actually an ideal protein source. Plant-based protein does not carry with it any of the negative consequences that animal-based protein does. Soy’s protein content is not a strong argument for eating soy, though, because people get enough protein just by eating a varied diet of whole foods.
A better argument for soy, and one that has caused quite a bit of confusion, is that soybeans contain phytoestrogens. Phytoestrogens are plant estrogens, which are not to be confused with human estrogens, although they frequently are.
Phytoestrogens have numerous benefits. Professor Walter Veith, in his health DVD Your Health Your Choice, cites some benefits of soy phytoestrogens. For example, new bone is built by cells called osteoblasts; older, more fragile bone is dissolved by osteoclasts. Phytoestrogens “make bone-dissolving osteoclasts less active…They stimulate the bone-building cells [osteoblasts] to build new bone…Genestein suppressed the activity of the bone-dissolving cells…Several studies have confirmed that the phytoestrogen genestein is almost as effective in preventing bone loss…as Premarin, the most commonly prescribed form of HRT (hormone replacement therapy)…But HRT causes cancer; genestein doesn’t.”
How do we get enough phytoestrogens such as genestein? Ground flax seed has the highest genestein content.
Professor Veith continues, “A Danish study…found that soy milk containing naturally high levels of phytoestrogens actually stops the bone loss that would otherwise occur in women after menopause. Women who consumed two glasses of soy milk daily, delivering 50 mg. of isoflavones over the 20 years [of the study] did not lose bone from their spines.” Yet “cow’s milk will cause bone loss.”
“In an Australian study conducted at the Royal Women’s Hospital in Melbourne, postmenopausal women experienced a 5% increase in bone mineral content when they ate 45 grams of soy grits every day for three months.” He pointed out we should be encouraged by the fact that the estrogen receptors most favored by phytoestrogens are those in the brain, bone, and breast. It is those areas where soy’s benefits are greatest, but one should not discount its positive effect in other areas, as well.
Finally, Professor Vieth notes that “rats fed carcinogens and complex carbohydrates show lower incidence of breast cancer than rats fed carcinogens and simple sugars.” Soybeans are among the many complex carbohydrates available to us.
Koreans, among others, have been eating soy for centuries. However, it is not eaten in the quantities consumed by those looking to replace meat in their diets with equal amounts of something else. Soy is an integral but small part of the Korean diet. Interestingly, Korean women don’t experience menopausal symptoms as Western women do.
Regarding soy specifically, one doctor pointed out:
“Rarely will you find billions of people embracing a food for centuries only to find they have been wrong.”
Pertaining to soy’s benefits, he cited research that found that “soy consumption rather than animal protein significantly decreased serum concentrations of total cholesterol, LDL and triglycerides in hypercholesterolemic individuals [those with high bad cholesterol levels], but not in normolipidemic individuals.” His journal article debunks many of the myths about soy.i
So does the research of John McDougall, MD, who points out the “Soy-food consuming populations of people, like the Chinese and Japanese, have a much lower incidence of heart disease, osteoporosis, and cancer of the breast and prostate.”
Regarding “the dark side to the soy story that warns that these foods may increase your risk for cancer, impair your thyroid, immune, and brain function, and cause you bone loss and reproductive problems,” he said that “fortunately, these worries are relevant mostly for people lured into consuming ‘fake foods’ synthesized from manmade components of soy and other foods, and high potency soy supplements—not for those who consume traditional soy foods as a small portion of their diet.
Therefore, he recommends “that you use traditional soy foods, like soy milk and tofu, only as a small part of your diet, at most 5% of your daily calories. Synthetic soy foods like meats, cheeses, and soy bars should rarely, if ever, be consumed. Examples of sensible uses might be soy milk to moisten cereal, not glassfuls as a beverage; tofu pieces in a stir-fry rice dish, not as a soy burger entrée; and an occasional tofu-based dessert, not daily soy ‘candy’ bars.”ii
It bears repeating that the closer the food is to the original condition it was in when harvested, and, when dealing with fresh fruits and vegetables, the sooner it’s eaten after it’s harvested, the better the food is for the body.
Tofu and other soy products are partially processed; we do not discourage their consumption, but we do suggest variety in foods and increasing the use of whole foods. As always, it is wise to read labels to see if any additives would make purchase of a processed food inadvisable. Some soy milks, for example, have sugar and other “flavor enhancers” added.
We warn concerning hexane, a neurotoxin used in the production of soy meal (flour), soy grits, soy oil, and soy protein (as in TVP, or in soy protein isolate or soy protein concentrate). Hexane can be found in soy bars, health food bars, many vegetarian products, some soy milks (many Silk soy products, for example), and even in baby formula. These products are made with soy bean flour, which is chemically treated with hexane. Enough traces of hexane remain to cause health warnings.
One can find conflicting information about the effect of soy on thyroid function. Mark Messina, PhD, and Virginia Messina, MPH, RD, in “Is It True What They Say About Soy?”iii wrote that “one study suggested that soy protein supplements can interfere with the absorption of thyroid medications. Other research tentatively showed that soy foods may actually interfere with normal thyroid function, perhaps leading to goiter (swelling of the thyroid gland, located in the neck). But there’s no risk of goiter in healthy people consuming soy who are not deficient in iodine. Strict vegetarians, who eat no iodine-rich fish or dairy products, might be at risk— and eating lots of soy might boost the risk. The answer is not to give up soy, but to increase iodine intake. One way is to use a small amount of iodized salt. One can also take iodine supplements or take kelp capsules or granules. And vary your diet as much as possible.”
In another article, Dr. Mark Messina stated that “as many as 10 percent of post-menopausal women may have subclinical hypothyroidism. This group may be sensitive to the adverse effects of weak goitrogens. The iodine status of the U.S. population is considered adequate, although there is a downward trend in iodine intake and subsets of the population may have marginal intakes. Any concerns about the effect of soy on thyroid levels can be definitively addressed by having thyroid hormone levels measured. Even this step is not unordinary, since the American Thyroid Association recommends that all people have their thyroid hormone levels checked every five years beginning at the age of 35.”iv
Drs. Messina also reported that the Mayo Clinic found that soy has not been shown to fuel breast cancer cells nor be linked to Alzheimer’s. They did caution against eating soy if one has had calcium-oxalate kidney stones, as “many soy foods are rich in oxalates and thus may promote the formation of such stones in those at risk….” On the plus side, they reported that the FDA has even “okayed a ‘heart healthy’ claim for soy foods because they reduce the risk of heart disease when eaten as part of a healthy diet. Soy helps lower high blood cholesterol and may work in other ways to benefit blood vessels and the heart. So far, of all the potential health benefits of soy, this one has the most solid evidence.”
There’s also confusion as to whether soy phytochemicals cause dementia. A closer look at the research on which such claims are based can resolve that issue in a way that is consistent with other research findings in this report.
A study that investigated the quality of the research study that came up with that warning reported that Dr. Messina found that “in this study [the one claiming a link to dementia], tofu consumption 2 to 4 times per week was classified as high intake. However, the HAAS had several design weaknesses. For example, the intake of only 26 foods was assessed. Nowadays, it is common for epidemiologic studies of this type to assess the intake of at least 100 foods. By assessing the intake of so few foods it is very difficult to control for potentially confounding variables. Perhaps tofu intake was associated with cognition because of dietary habits common to tofu consumers and not because of tofu consumption per se. Also, the intake questions pertaining to tofu differed from one time point to the next so the authors had to devise a somewhat convoluted method for classifying men based on different intake responses.”
The author’s report continues as follows:
There were just too many design flaws to take the HAAS study as gospel. So what about other research that examines the possible connections between soyfoods and dementia? Dr. Messina describes another study that indicated tofu to be the cause of cognitive problems, but the real culprit was probably formaldehyde. “One other recently published epidemiologic study raised questions about soy and cognition. This was a small Indonesian study carried out in 2 rural sites (Borobudur and Sumedang) and 1 urban site (Jakarta) among mainly Javanese and Sundanese elderly (n = 719, 52 to 98 years of age). High tofu consumption (at least 9 times/week) was associated with worse memory. The authors speculated that isoflavones might be responsible for the association. However, high tempeh (a fermented whole soybean product) consumption was independently related to better memory particularly in participants over 68 years of age. Tempeh is also very high in isoflavones. The paradoxical findings (two soyfoods high in isoflavones having opposite effects) are likely due to the fact that according to the Departments of Public Health at the Universities of Jakarta and Yogyakarta, formaldehyde is added to tofu (but not tempeh) to preserve its freshness. Formaldehyde causes memory problems in animals. Of course, formaldehyde is not used as a food preservative in the United States.”
Another study showed no effect of soy on brain function at all. “In contrast to the Hawaiian and Indonesian studies, a cross-sectional study, which included 3999 men and women aged 65 years and older from Hong Kong, found that isoflavone intake was unrelated to cognitive function as assessed by the cognitive part of the Community Screening Instrument for Dementia.”
So no published studies successfully back up the claim that soy shrinks your brain or causes dementia. Rather than being harmful, could there possibly be cognitive benefits from eating soy? Maybe for some women. Dr. Messina continues, “Finally, and even more importantly, the 10 clinical trials that have examined the impact of isoflavone-rich products on cognitive function actually suggest that at least in younger postmenopausal women, isoflavones favorably affect several aspects of cognitive function.”
“At this point, it is not possible to draw conclusions about the impact of soy or isoflavones on cognitive function although generally speaking, intervention studies – which are suggestive of benefit – carry more scientific weight than epidemiologic studies, which show mixed results.”v
The primary originator of warnings about soy seems to come from the Weston A. Price Foundation and, in lesser degree, smaller organizations which rely on the same flawed information. It is wise to investigate what the foundation advocates, and the basis for their advocacy. What is the credibility level? Sally Fallon is the founder of that foundation, having been impressed with the nutrition research of dentist Dr. Price. She is also author of Nourishing Traditions, in which she recommends animal fats and cholesterol, among other things, as necessary elements of a healthy diet.
In her book and lectures, Fallon also recommends “traditional” fermented foods, yet every mention of fermentation in the considerable health writings of Ellen White is in the context of warning due to harmful impact to the digestive system, not commendation.
In addition to the Weston Price Foundation’s specific warnings not to eat soy products, the foundation advocates fermented foods, liberal use of animal fats, “full-fat milk products,” meats from pasture-fed animals, and regular intake of cod liver oil.vi However, the foundation’s credibility is questioned in print and online by a significant number of scientific researchers and investigative websites such as www.quackwatch.org and navigator.tufts.edu. The latter site states that the Weston Price Foundation “‘appear[s] to select obscure studies, take study results out of context, and use undocumented “facts” from their own publications to forward their agenda.’ They go on to point out that the promotion of raw milk presents a food safety risk and that the practice of feeding whole cow’s milk to babies, as promoted by WPF, is discouraged by the American Academy of Pediatrics.” The Tufts Nutrition Navigator scored the Weston Price website as “unacceptable,” with an accuracy rating of 1 out of 10 possible points. Quack Watch cites Dr. Price’s research on so-called “natives” as founded on “poorly designed studies” that jump to “simplistic conclusions.”vii
Most telling, perhaps, is that much of the Weston Price Foundation’s recommended diet is in stark opposition to the conclusions drawn from The China Study, which is the largest, the most comprehensive study ever done on the correlations between diet, disease, and mortality. It was carried out in China, where there is up to a one-hundredfold difference in cancer incidence among different locales. Cancer is a localized disease in rural China, present in one village but totally absent in another village. Diet is the differentiator. In the US, however, where we tend to eat the same things nationwide, cancer is regarded as a national affliction. Indeed, in the US we have only a twofold difference in cancer incidence between different areas.
The New York Times called The China Study the “Grand Prix” of scientific investigation into nutrition and disease. Its findings are almost impossible to refute. T. Colin Campbell, the project’s coordinator and author of the book The China Study,viii reports the study’s startling finding of a linear relationship between consumption of animal foods and disease states. As the consumption increases—even in small amounts—so does disease. But the higher the level of antioxidants in the blood, which is obtainable only from plants, the less disease there was.
Dr. Campbell reports the study’s findings about “controlling cancer through nutrition.” Casein, a protein from milk, was used in lab experiments, and the question was raised, “Did it make a difference what type of protein was used in these experiments?” Would wheat or soy protein, for example, cause the same effect? It was found that “plant protein did not promote cancer growth, even at the higher levels of intake.”xi
The point being made here is that the main opponent of soy and soy products is a foundation whose dietary recommendations, which emphasize significant consumption of full-fat animal and dairy products, leave much to be desired and often run markedly contrary to predominant research findings indicating the deleterious effects of consuming a diet rich in foods of animal origin. One must be most cautious before embracing any other nutritional advice they might offer.
In summary, soy is a beneficial nutrition source for both humans and animals. The cautions revolve primarily around genetic modification, hexane use in processing, the importance of dietary variety, and highly-processed soy products.
vi “Dietary Guidelines,” from brochure “The Weston A. Price Foundation for Wise Traditions in Food, Farming, and the Healing Arts.”
vii T. Colin Campbell, The China Study (Dallas: Benbella Books, 2005).
viii Ibid: 59-60.
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