While certain animal studies have led to a misunderstanding of soy and immunity, there is, in fact, no scientific evidence showing that soy negatively impacts the immune system in humans. In animal studies, rodents exposed to very high quantities of isolated compounds found in soybeans displayed changes in immune function. However, both positive and negative changes were observed. Studies in humans suggest that soy has either no effect on the immune system, or may actually enhance immune function.1
1. Ryan-Borchers TA, Park JS, Chew BP, McGuire MK, Fournier LR, Beerman KA. Soy isoflavones modulate immune function in healthy postmenopausal women. Am J Clin Nutr. 2006 May;83:1118-25.