The Soy-ling of America: Second-Hand Soy from Animal Feeds

People who are allergic to soy may also react to eggs, dairy and flesh foods. This is usually chalked up to multiple allergies, but the cause might well be soy residues from the soy-based chows fed to poultry, cows, sheep and fish.

Since 2005, when The Whole Soy Story:The Dark Side of America’s Favorite Health Food was published, many readers have shared stories of allergic reactions to eggs, dairy and meat from soy-fed animals. Not a lot of science supports the premise that soy feed is the culprit just yet, but four studies indicate phytoestrogens end up in egg yolks, and one shows their presence in chicken liver, heart, kidney and muscle meat.

In a 2001 article in Bioscience, Biotechnology and Biochemistry,1 researchers from the Food Research and Development Laboratories of the Honen Corporation, of Shizuoka, Japan, described feeding hens a diet containing a high concentration of soy isoflavones, and then measured the isoflavones in plasma and egg yolk. Over an eighteen-day period, the concentration of isoflavones peaked on the twelfth day with isoflavone levels in the egg yolk at 65.29 μg per 100 g. This value remained constant throughout the rest of the experiment.

The researchers announced a lowering of cholesterol in the egg yolk on day three, the point at which the isoflavone concentration in the yolk jumped up, but were disappointed to find the cholesterol returned to the basal level soon after. With the soy industry champing at the bit at the prospect of selling high-isoflavone chicken feeds so hens could produce low-cholesterol eggs, this finding was not good news. However, all was not lost, since the findings do support a profitable future of selling high-isoflavone eggs to health-conscious consumers who perceive soy as a miracle food for easing menopause and preventing heart disease, cancer, osteoporosis and other ills.

In 2004, the researchers followed up with a second study published in Biochimica et Biophysica Acta.2 This time they reported the “good news” that they had not only found plenty of the soy isoflavone daidzin but the more active form known as equol “preferentially accumulated” into egg yolk. This was pleasing news for the soy industry indeed as it would “raise the possibility that feeding domestic animals soy-based fodder produces animal-based foods rich in a more active form of phytoestrogens.” The assumption, of course, is that once again health-conscious consumers will jump at the chance to buy premium-priced super eggs not only rich in phytoestrogens, but in the active form of equol.

In 2004, University of Maryland researchers published their findings in the Journal of Agriculture and Food Chemistry.3 This team fed Japanese quail rations supplemented with the soy isoflavone genistein, and reported the isoflavone genistein and its metabolites in the egg yolk, but not in the white. Although trace amounts of genistein also showed up in the controls, those quail fed the genistein-enriched diet showed much higher concentrations in their eggs after three days of supplementation and for two days past the special feeding. Previously this team had focused on the impact of endocrine disrupting chemicals, including pesticides, herbicides, industrial products and plant phytoestrogens, on reproductive and neuroendocrine function in Japanese quail.

In 2009, grad student Dante Miguel Marcial Vargas Galdos at Ohio State University completed a master’s thesis entitled “Quantification of Soy Isoflavones in Commercial Eggs and their Transfer from Poultry Feed into Eggs and Tissue.”4 Forty-eight laying hens were fed three types of chicken feed: a soy-free feed, a regular feed containing 25 percent soybean meal or a special feed that packed 500 mg soy isoflavones per 100 grams.

Vargas Galdos succeeded in his goal of proving the transfer and accumulation of isoflavones from chicken feed into hen eggs and tissues. Chickens fed the special chow with the extra 500 mg isoflavones per 100 grams laid eggs with yolks containing 1000 μg isoflavones per 100 grams. Chicken livers, kidneys, hearts and muscles contained 7162 μg per 100g, 3355 μg per 100g, 272 μg per 100g and 97 μg per 100g, respectively. He found no soy isoflavones in the eggs laid by hens fed soy-free Cocofeed obtained from Tropical Traditions. Although these chickens had grown up on the regular 25 percent soy protein feed, no trace of soy isoflavones remained in their eggs ten days after switching to the soyfree alternative.

Vargas Galdos’s research also included measuring the isoflavone content, including equol, of eighteen brands of eggs currently on the market. Not surprisingly, all brands of commercial or organic eggs, whether free range or caged, contained soy isoflavones, with the total isoflavone content per egg ranging from 33μg to 139μg per 100g of egg yolk. These samples were all from hens fed a soy-based feed as is typical of eggs now sold both in supermarkets and health food stores.

Although variations occurred from egg to egg, there was no significant difference in isoflavone content among the different brands with the exception of those eggs high in omega-3 fatty acids. A premium brand that claimed an omega-3 concentration of 600 mg per egg showed a significantly lower isoflavone content, presumably because flax seed or fish rations replaced some—though not all—of the regular soy feed.

The takeaway? In the words of Vargas Galdos, “The results showed that diet can be altered to modulate isoflavone content in hen eggs and tissues.”

“Modulate” indeed! In plain English, these researchers hope to push more soy on an unsuspecting public. For our own good, of course! The idea is farmers should feed their poultry and other animals more soy — particularly isoflavone-enriched soy. That way all of us foolish people who don’t choose a soy milk shake or “Tofu Scramble” for a healthy breakfast can experience the miraculous health benefits of soy from eating scrambled eggs. We can thus eat soy that does not look like soy, taste like soy or is required to be labeled as soy. Labels on such “designer eggs” will not be required to name soy, any more than current cartons do.

This represents a clear and present danger for individuals with soy allergies, and for anyone who wants to avoid over-estrogenization (such as growing boys and women prone to breast cancer). And a Food Rights/Freedom of Information issue for the rest of us.




Odwalla’s Chocolate Protein Monster, deceptively described as a “dairy-based beverage,” made the news last April when four consumers experienced severe allergic reactions. This set off a “nationwide allergy alert”, a product recall and a lot of speculation about what might have caused the reactions. Although all four of the victims were allergic to peanuts, and two were also allergic to tree nuts, the drink contained neither peanuts nor tree nuts. There was also no evidence of accidental or malicious cross contamination at the manufacturing plant.
With the possibility of contamination from peanuts unlikely, detectives are considering the potential for cross reactivity. Cross reactivity refers to a reaction that occurs when people allergic to one class of proteins react to another similar in structure. A good example is soy and peanuts, members of the grain-legume botanical family. In fact, scientists have known for years that people allergic to one are often allergic to the other. Food safety experts say they are clueless as to what might have happened in the Odwalla case, but given that the Chocolate Protein Monster drink contained soy protein, and the victims all suffered from peanut allergies, the likely culprit is soy.
Severe reactions to soy were once rare. Today they are increasingly common, and pose especially high risks to children already afflicted with peanut allergies. In 1999, the journal Allergy reported that four children in Sweden died after eating a minuscule amount of soy “hidden” in hamburgers. The Swedish National Food Administration promptly warned parents and pediatricians of the soy-peanut link, and stated that children suffering from both peanut allergy and asthma are at very high risk. Additional risk factors reported included other food allergies, a family history of peanut or soy allergies, a diagnosis of asthma, rhinitis or eczema, and/or a family history of those diseases. The researchers found it took only a tiny, almost indiscernible, amount of soy to create a severe and even life-threatening reaction in susceptible individuals. Even more surprising, they discovered severe allergic reactions could happen suddenly and unexpectedly to people with no known soy allergies. In fact, the reactions documented by the Swedes were very similar to the reactions to the Odwalla Chocolate Protein Monster drink.
Tragically, the Swedish National Food Administration warning has not been publicized much in the U.S. Indeed, the Soyfoods Association of North America – and even many allergy support groups – recommend soy nut butter and soy nuts for children allergic to peanuts and tree nuts. As a result, few people have heard of the deadly soy/peanut connection, and numerous adverse reactions have been reported.
Worse, there have also been several deaths. Six years ago, 13-year-old Emily Van Der Meulen died on April 13, 2006. Emily had a severe peanut allergy and assiduously avoided peanuts, but did not know she should also have avoided soy. She died after eating a meal that was apparently peanut free but contained a tiny amount of soy. Just as in the Swedish study, she had not previously reacted to soy.
On February 22, the Weston A. Price Foundation learned the sad news of the death of a nine-year-old girl who was allergic to peanuts but died after drinking soy milk: “My cousin’s daughter passed yesterday after having soy milk for the first time. She was known to have peanut allergies and asthma. My cousin watched what she ate but he was not aware of the relationship between the peanut allergy and soy. She had an asthma attack and did not respond to treatment.” Hundreds of other mystery deaths may also have been caused by the soy-peanut connection. Indeed, it’s a question that needs to be asked whenever we hear someone with peanut allergies dies suddenly after eating a hamburger, a burrito or some other food that did not contain peanut ingredients. The obvious question is, why so many reactions, and why now?
The main reason appears to be the increased number of allergenic proteins found in genetically modified (GMO) soy. As reported by Robyn O’Brien on the AllergyKids website: “According to previously undisclosed research and the Peanut Genome Initiative, it appears that in the genetic engineering of soy, a soy allergen was created that is 41 percent identical to a known peanut allergen, ara h 3. This new allergen, now found in soy, is recognized by 44 percent of peanut allergic individuals. Recent studies out of the University of London conducted by Gideon Lack support this undisclosed research and highlight the role that conventional soy (and soy formula) play in the development of the peanut allergy. . . In the United States, 90 percent of soy now contains these new proteins, chemicals and allergens.”
Why hasn’t this news gotten out? Why do so many allergy support groups neglect to issue warnings? Given the fact that soy ingredients are in more than 60 percent of processed or packaged foods and nearly 100 percent of fast foods, this is simply irresponsible. Not surprisingly, the reason appears to be the usual principle of profits over people. According to Robyn O’Brien, “Leading pediatric allergists and researchers have been funded by the agrichemical corporation responsible for engineering these proteins, chemicals and toxins into soy.”
Will the Odwalla case bring this lifesaving information into the mainstream media? As yet, the culprit hasn’t been identified as soy. Until then, we can only hope, pray, and make a concerted grassroots effort to share this information with as many people as possible.




1. Saitoh, S.; Sato, T.; Harada, H.; Takita, T. Transfer of soy isoflavone into the egg yolk of chickens. Biosci. Biotechnol. , Biochem. 2001, 65, 2220-2225.

2. Saitoh, S.; Sato, T.; Harada, H.; Matsuda, T. Biotransformation of soy isoflavone-glycosides in laying hens: intestinal absorption and preferential accumulation into egg yolk of equol, a more estrogenic metabolite of daidzein. Biochim. Biophys. Acta 2004, 1674 (2) 122-130.

3. Lin, F.; Wu, J.; Abdelnabi, M.; Ottinger, M.; Giusti M.M. Effects of dose and glycosylation on the transfer of genistein into the eggs of the japanese quail (Coturnix japonica). J. Agric. Food Chem. 2004, 52, 2397-2403.

4. Vargas Galdos, Dante Miguel Marcial. Quantification of Soy Isoflavones in commercial eggs and their transfer from poultry feed into eggs and tissues. Thesis. Ohio State University, Food Science and Technology Graduate Program, 2009;


This article appeared in Wise Traditions in Food, Farming and the Healing Arts, the quarterly journal of the Weston A. Price Foundation, Summer 2012.

Kaayla T. Daniel, PhD, CCN, is The Naughty NutritionistTM because of her ability to outrageously and humorously debunk nutritional myths. A popular guest on radio and television, she has appeared on The Dr. Oz Show, ABC's View from the Bay, NPR's People's Pharmacy and numerous other shows. Her own radio show, "Naughty Nutrition with Dr. Kaayla Daniel," launches April 2011 on World of Women Radio. Dr. Daniel is the author of The Whole Soy Story: The Dark Side of America's Favorite Health Food, a popular speaker at Wise Traditions and other conferences, and recipient of its 2005 Integrity in Science Award. Her website is and she can be reached at

One Response to The Soy-ling of America: Second-Hand Soy from Animal Feeds

  1. Megan Hopkinson says:

    My 6 year old daughter who is allergic to both peanuts and treenuts, had an anaphylactic reaction after having a few sips of Shaklee’s Cinch Vanilla Soy “non GMO” soy isolate protein shake. She never had an issue w/ soy prior to this horrible reaction. A sample of the shake tested negative for peanut and treenut protein. I would love more info on this. We have been in touch w/ Dr. Taylor @ FARRP and I would love to know if their is a link between the Odwalla product and Shaklee’s soy product. Maybe they get their soy isolate protein from the same manufacturer.

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