Soy

Check out Eco Salon's recent eye opening article "Debunking the Most Popular Soy Myths." I was surprised to find out that soy is among the 8 most common food allergens, "with reactions to be particularly common among children" and that goat's milk is second best to breast milk.
http://www.ecosalon.com/10-things-you-must-know-about-soy-before-you-eat-it-again/