Hypothyroidism includes a lot of different ailments. If it's Hashimoto's, it's an immune system disorder, for example. If it isn't an immune system disorder, it's most likely an iodine deficiency, which can be treated with seaweed, usually bladderwrack and kelp or kombu or hijiki. Every vegetarian should be eating seaweed anyway, since it's a good source of minerals. But the unsaid truth is, some people do great as vegetarians, and some don't.