Soy allergies result from a reaction to the protein found in soybeans. Soy-based foods include edamame (soybeans), tofu, tempeh, soy butter, soy sauce, soymilk, and miso. It’s also an ingredient in many processed foods, including vegetarian meat substitutes. Soybeans are a legume. So if you’re allergic to soy, you could be allergic to other legumes, too.