http://www.mayoclinic.org/diseases-conditions/hypothyroidism/expert-answers/hypothyroidism-diet/faq-20058554

There's no evidence that eating or avoiding certain foods will improve thyroid function in people with hypothyroidism.

I have Hashimoto's (autoimmune thyroid disease), and my endocrinologist told me to eat whatever I want—just eat less of it than when I was gaining. I eat soy, seaweed, carbs, gluten, all the vegetables… I lost the weight—and kept it off.

If you find you react to something then it is probably best avoided. As with all things, do what is right for yourself.

If you start restricting foods you will be reducing the spectrum of necessary substances contained within them. I react to soy in general and as lecithin in particular, it can sneak into a chocolate bar, when you would think this presence would by minuscule. Sunflower lecithin is available. Links are also being made between a person not being able to take maize as a possible indicator of thyroid problems, (think pill binder/common in low fat foods)(its me as well).

If you know you have many food related reactions it may be worth while looking into this closer. Salicylate can be one of the umbrella problems, it is present in non animal foods but not all (blue cheeses do) and as aspirin and associated medications which caused inflammation within me. There are now some indications "inflammation" within the body can set up an autoimmune response or responses. To investigate this by blood and or urine testing is a personal decision best done with an appropriately trained person, doctor or nutritionist or what ever.

Because something "can" happen does not mean it will in your or every personal situation.

My concern with soy is its overuse in food products. It is so commonly used as a filler for a variety of reasons. I don't avoid it at all and I have Hashi's as well.

Soy contains phytoestrogens which act the same as oestrogen and can interact with the uptake of levothyroxine/synthroid that said i don't avoid it if it is added as an ingredient such a soy lechitin and i use soy sauce when i cook chinese or indonesian food. I don't have any products where the main ingredient is soy though and won't eat soy beans as a whole food either but that is because from experience they make my hypo symptoms worse. You have to really see and try what works for you by listening to your body its the only way to find out.

I have Hashimoto's disease. I drink Soy milk everyday and eat foods that contain soy during the week. There has been no issue at all with my Thyroid levels. Been on the same dose of Synthroid for years. My doctor has never told me avoid any types of foods.

I dont do soy or gluten. I cut out both about a month ago and feel 100x times better. I found for myself the combination of the diet change and my medication makes me feel alot better than just the medication alone. Not to mention im going on 20lbs lost in a months period of time. You need to expierenment and figure out what works best for you.

for what it's worth, doc told me to limit soy and not to eat any within 4 hours of taking levothyroxine.