I’ve never been advised about soy, caffeine or other foods. I do not eat or drink anything but water for 30 mins after taking it. You may have special circumstances or a particularly conservative doctor while I’m just under the care of a primary Dr. I am not the healthiest vegan, so I do enjoy soy based replacement foods.
Quick search on Mayo site: https://www.mayoclinic.org/diseases-conditions/hypothyroidism/expert-answers/hyperthyroidism/faq-20058188
Is it true that people who have hypothyroidism should avoid soy?
Answer From Juan Brito Campana, M.B.B.S.
For most people with hypothyroidism, it's okay to have some soy. But the timing of when you have it makes a difference.
Treatment for hypothyroidism usually includes taking the thyroid hormone medicine levothyroxine (Levo-T, Synthroid, others) every day. Research has shown that soy can make it harder for the body to absorb that medicine. But people who have hypothyroidism don't need to avoid soy completely.
If you have hypothyroidism, follow your health care professional's directions for how to take thyroid hormone medicine. In general, it's best to take the medicine on an empty stomach. And take it at the same time every day. Many people take this medicine first thing in the morning.
Wait at least one hour after taking thyroid medication before you eat or take other medicines. That includes food or drinks that have soy in them. There also are other ingredients in food, drinks, medicines and some dietary supplements that can affect the body's ability to absorb thyroid medication. Examples include iron, calcium and fiber, among others.
If you have questions, talk to your health care professional about how and when to take your thyroid hormone medicine.
Good luck! 
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