Atkins won't cause a thyroid problem, thyroid problems are due to autoimmune diseases (usually), or iodine deficiency, which are most likely due to a lifetime of eating bad stuff and/or genetics.

What Atkins, and any low calorie diet, will do is cause the amount of RT3 your body makes to go up. People who do calorie restricted diets as well as low carbers get this effect. It's simply the body's way of making sure you don't starve to death. It is temporary and should stop when you stop dieting.

There have been some information posted that as little as 50g of carbs is needed to avoid that in Atkins, but that assumes you're not low calorie too.

I can't lose on 50g of carbs. In fact, I can't even maintain my weight on that much carb. So I stick with lower carbs than that.

A lot of thyroid patients have found that the hCG diet works well for us. I posted something here not too long ago bout that.