❓What should vegetarians who are allergic to soy do — where does their protein come from?

Soy products really are an important protein source for vegetarians, so once you're allergic, you need to be more deliberate about getting enough protein from other places. Options include: grains like quinoa (decent protein content and quality, and it's a complete protein) and oats; other beans besides soy (some people allergic to soy aren't actually allergic to red beans, mung beans, chickpeas, or lentils, since the allergenic proteins aren't identical — but if you're allergic to legumes as a category, you'd need to avoid all of them, so it's worth getting detailed allergy testing done to confirm exactly what range applies to you); nuts and seeds (if you're not also allergic to those), like pumpkin seeds, sunflower seeds, or almond butter; if you eat eggs and dairy, eggs, cheese, and Greek yogurt are all good-quality protein sources; and seitan/kaofu (if gluten isn't an issue for you) is a solid option too. How far a soy allergy extends really varies from person to person, so it's best to get a clear evaluation from an allergist rather than guessing at how wide or narrow to make your avoidance list.