Lectins are drawn right to that lining, and your immune system retaliates. Lectins are found in all foods, but in some more than others. All seeds of the grass family - wheat, rye, rice, spelt, etc. - are high in lectins. You also find lectins in beans, dairy and in the nightshades (tomatoes, potatoes, eggplant). According to a 1991 study, dairy may be potentially more harmful in pasteurized, processed milk because of the reduction of SIgA, an immunoglobulin that binds dangerous lectins.