I'm pretty sure it's soy. There's a popular brand of meatless burgers that I can't tolerate but their sausage links and black bean burgers are fine. There's another popular brand that I have no problem with at all. And like I said I love the Gardein meatballs but I don't care for their other plant-based products. I took some Gas-X (sorry, TMI I know) last night and I'm a little better but nauseated today. I know now not to buy that brand of "sausage".