A hormone-like compound found in soy products, including soy-based infant formulas and menopause remedies, may impair immune function.
When mice were injected with the "plant estrogen" genistein, which is found in soy products, levels of several immune cells dropped and the thymus, a gland where immune cells mature, shrank.
Of course, people eat rather than inject soy products, but the thymus also became smaller in mice that consumed genistein in their diet. This is particularly concerning, researchers say, since the resulting blood levels of genistein in the mice were lower than those reported in human babies fed soy formula.
A few reports from the late 1970s and early 1980s suggested that a soy-based diet impaired infants' immune functions. About 15% of infants in the US, or roughly 750,000 children, consume soy-based formula each year.
Proceedings of the National Academy of Sciences May 21, 2002;99:7616-7621
It is quite amazing that this study was actually published as the findings were quite negative for soy and yet it was funded by the United Soybean Board and the Illinois Council on Food and Agricultural Research.
Amazing, it seems that eventually the truth on soy does reach the service, despite the massive funding by the edible oil industry to convince the public that soy is the greatest thing that ever hit the planet to improve your health.
A 1997 Lancet study showed that soy has glycosides of genistein and daidzein or plant based chemicals that mimic estrogen. They possess a wide range of hormonal and non-hormonal activities. The daily exposure of infants who consume soy formulas was 6-11 times higher than adults consuming soy foods.
The blood concentration of these hormones was 13,000 to 22,000 times higher than estrogen in the blood. The authors of this article speculate that this concentration may be sufficient to exert biological effects, whereas the contribution from breast-milk or cow-milk is negligible.
Soy formula is one of the worst foods that you could feed your child. Not only does it have profoundly adverse hormonal effects as discussed above, but it also has over 1000% more aluminum than conventional milk based formulas.
I don't recommend either, but if one, for whatever reason, cannot breast feed, then Carnation Good Start until six months and Carnation FollowUp after that seem to be the best commercial formula currently available. The milk protein is hydrolyzed 80% that tends to significantly decrease its allergenicity.
It is also important to note that when breast-feeding it is wise to avoid drinking milk as it has been shown for several decades that the milk will pass directly into the breast milk which can cause potential problems in the infant.