What causes thyroid imbalance? And what causes weight gain with a thyroid imbalance?

Many causes,low met. There are many causes of thyroid imbalances but our growing exposure to toxins including Fluoride (yes, fluoridated water causes it), bromine ; mercury is likely the most common cause. See http://bit.Ly/1doksyi ; http://bit.Ly/1ddkbiq for details. Thyroid hormone controls our metabolic rate like the rate an engine idles. The resultant slow metabolism in hypothyroidism causes weight gain.