Ccotta -- here's some of the argument against soy, right along with your doc:

Soy also depletes and interferes with iodine levels. Iodine comes from foods like seaweed and wild fish. Since a vegetarian diet doesn’t include fish and is usually high in soy, vegetarians can quickly run into imbalances that affect the delicate thyroid gland. Thyroid health is so important for a robust metabolism, as well as for maintaining lean muscle mass and day-to-day energy.