This first appeared in my facebook news feed and I really didn't think much of it at the time. As a breastfeeding advocate and a lactation educator, it's sometimes hard to filter the anti-formula rhetoric through the lens of critical thinking, and since I work predominantly with breastfeeding mothers and not formula feeding mothers, I usually don't need to do that. But then someone asked me, point blank, if soy formula contained the equivalent of 3 birth control pills. I got to thinking and I realized that on the surface, that claim sounded ludicrous. But is it?
Tracking down the origins of this claim was incredibly difficult, and there are a couple different versions, ranging from "3 pills per day" to "3 pills per serving". I still cannot find a single reputable source of that claim. In fact, the original post that showed up in my newsfeed seemed to attribute it to calculations by the Swiss Federal Health Service, but didn't provide a reference for those calculations.
Finally, I was able to isolate a similar statement to the Weston A Price Foundation (specifically one of their honorary board members, Mike Fitzpatrick). According to the 2004 article published by WAPF:
"The most serious problem with soy may be its use in infant formulas. "The amount of phytoestrogens that are in a day’s worth of soy infant formula equals 5 birth control pills," says Mike Fitzpatrick, a New Zealand toxicologist." [2]
In a previous 2002 piece titled "Soy Formula: Birth Control Pills for Babies", WAPF said:
"According to a Swiss report, 100 mg isoflavones taken by adult women provide the estrogenic equivalent of a contraceptive pill.10 This means that 10 mg provides the estrogenic equivalent of a contraceptive pill to a baby of 6 kg. Thus, the average amount taken in by a child on soy-based formula provides the estrogenic equivalent of at least 4 birth control pills." [1]
So let's take a look at both of those sources.
Mike Fitzpatrick, New Zealand Toxicologist
Mike Fitzpatrick is a New Zealand toxicologist and campaigns against soya foods. He is an honorary board member of the Weston A Price Foundation. The quote attributed to him did indeed come directly from him in 1995, but has been clarified by him in later years.
"When I first did my review, I did compare the estrogenic equivalents of the contraceptive pill with how much soy infants and adults would be consuming. It’s at least the equivalent of one or two estrogen pills a day, on an estrogenic basis. I’ve been criticised that it’s not the same form of estrogen, but in terms of estrogenicity, it’s a crude but valid and alarming statistic." [6]
So not exactly 5 pills, but he still maintains that it's the equivalent of 1 or 2.
The Swiss Report
This one is much harder to verify and I have not been able to completely verify it. It was originally published in the Swiss Government's Bulletin de L'Office Federal de la Santé Publique, in 1992. [7] Unfortunately that was before the wide availability of online publications, and the government of Switzerland only has online access to their official bulletins from the last 13 years.
But on the note of this study, I disagree with the way the WAPF interpreted and applied the calculations. The bulletin referred specifically to the birth control equivalent of a soy isoflavone supplement taken by adult women. Without knowing which specific isoflavone or combination of isoflavones in the supplement, it's hard to apply that research to all soy-containing products. Different species of soy plants have different levels of Genistein and Daidzein isoflavones, and even crops harvested at different times of the year can have up to 50% variability in their isoflavone content.
According to the USDA Database for the Isoflavone Content of Selected foods (2008), the isoflavone content of Similac Isomil ready-to-feed soy formula is:
Those figures are represented in mg per 100 g of food consumed. [3] If we adjust them based on the daily intake of soy formula per day we end up with 936 grams (33 ounces) of infant formula, leading to daidzein intake of 6.83 mg, Genistein intake of 12.82 mg, a Glycitein intake of 1.12 mg, resulting in daily total isoflavone intake of 20.69 mg/day.
On the surface, that would look to line up correctly with (and be even higher than) the WAPF's assertion that 10 mg of isoflavones is the equivalent of 1 birth control pill in a 6 kg infant. But it's complicated by the realization that just having a certain isoflavone content does not mean it will have an exact effect on the body the way synthetic estradiol in birth control pills does.
A review of the literature was published in the Annual Review of Nutrition in 2004. Entitled "Isoflavones in Infant Formula: A Review of Evidence for Endocrine and Other Activity in Infants," [4] the study specifically calculated the amount of soy isoflavones consumed per day by infants in relation to actual birth control pills.
"Estrogen intake from modern oral contraceptive pills ranges from 20µg/day to 50µg/day. If we assume the average weight of women taking such pills is 50 kg, the daily estrogen intake is 0.4–1µg/kg/day. As for infants fed with soy formula exclusively, the total daily genistein intake is about 5 mg/kg/day (70% of total isoflavones). Because the estrogenicity of genistein relative to estradiol varies widely depending on the method used, the relative quantitative estimation of bioactive dose of genistein is also variable. A 10−3 or 10−5 relative estrogenicity of genistein to estradiol would yield a relative intake of 5µg/kg/day or 0.05µg/kg/day estradiol for these infants."
In other words, the actual estrogenicity of genistein and soy isoflavones is not equivalent to the estrogenicity of actual estradiol. These isoflavones exert a much lower estrongenic effect than actual estrogen, and on an actual molecular level in the human body that estrogenic effect can be quite variable.
Another important point mentioned by the authors was that most infants who consume soy formula do not do so from the start. The switch to soy formula is usually undertaken in older infants after colic, gas, or allergy has been suspected from cows milk formula.
From a purely symptomatic angle, it's reasonable to expect that if infants were consuming the equivalent of 3-5 birth control pills per day from soy formula, that we would see more clinically significant effects, with regards to these hormonal side-effects. In women, just consuming 1 birth control pill per day can regulate menses, prevent pregnancy, and cause other hormonal effects. Soy formula has seen about 50 years of use, with no major clinically significant effects in infants. It's well known that infants do respond to estrogens, and it's also generally accepted that infants fed soy formula consume the largest concentrations of soy isoflavones than all the other soy-eating groups. But what is not well known is what effect, if any, it's actually having.
What we can deduce, based on this information, is that the claim of soy formula being 3-5 birth control pills is likely overblown and does not represent the actual estrogenic effects of the amount of isoflavones consumed from soy formula. That does not mean that soy formula does not have it's own set of unique risks. There are additional concerns about the affect of the isoflavones on thyroid function, risk of allergy, and the fact that soy formula contains higher amounts of aluminum than cows milk formula. For some infants, consuming soy formula is unavoidable, such as in the case of galactosemia. But recognizing the risks and implications of a soy-based diet in infancy does not need to involve overblown claims of giving infants birth control pills.
References:
1. Weston A Price Foundation, 2002, "Soy Infant Formula: Birth Control Pills for Babies" http://www.westonaprice.org/soy-alert/soy-formula-birth-control-pills-for-babies
2. Weston A Price Foundation, 2004, "Soy and the Brain"
http://www.westonaprice.org/soy-alert/soy-and-the-brain
3. US Department of Agriculture, 2008, "USDA Database for the Isoflavone Content of Selected Foods" http://www.ars.usda.gov/SP2UserFiles/Place/12354500/Data/isoflav/Isoflav_R2.pdf
4. Annual Review of Nutrition, 2004 24:33-54, "Isoflavones in Infant Formula: A Review of Evidence for Endocrine and Other Activity in Infants" http://courses.biology.utah.edu/carrier/3320/Endocrine%20disruptors/soy%20and%20infants.pdf
5. Food Renegade, 2013, "Soy Infant Formula: A Formula for Disaster"
http://www.foodrenegade.com/soy-infant-formula-formula-for-disaster/
6. "In Unusual Letter, FDA Experts Lay out Concerns", 2002, Daniel Sheehan, Danial Doerge
7. Bulletin de L'Office Fédéral de la Santé Publique, no. 28, July 20, 1992.
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