That is a really good question, and I am not sure I can completely answer it. What the thyroid does is release hormones that control cellular metabolism-how fast your metabolism works. More than likely if your metabolism is slowed down due to an inadequate amount of T4 and T3 (the two hormones made by the thyroid) that also means that the amount of fat burning is slowed down. HOWEVER, any change in the ketostix means you are in ketosis-many people here believe that the darker color on the ketostix means you are dehydrated.