Dear T.,
I too have thyroid disease, and thyroid issues are not like elevated cholesterol or diabetes that can be controlled or maintained through diet - at least not to my knowledge.
However, loosing weight can help with the dosage of synthroid you need to take.
After my diagnosis of Hyperthyroidism, Graves disease, I did the Radioactive Iodine treatment which left my thyroid 'useless' and I was put on Synthroid too. I gained an enormous amount of weight while we tried to get my levels under control... it was a long process.(several years!) Once I made up my mind to loose weight, (I lost 40+ lbs) I was able to lower my dosage of synthroid & feel soooooo much better. Apparently, weight can play a major role on how much of the synthetic thyroid hormone your body needs. Here's how I did it. GIVE UP ALL SOFT DRINKS! regular and Diet, and replace them with ICE water. Take a brisk walk for 15 mins each day.
You will see results in a short time, which will help keep you motivated.
Good luck and have a very Merry Christmas!!!
S.