Thyroid hormones are responsible for the conversion of stored body fat into free fatty acids -- the only form of fat the body can use for fuel. Neither thermogenesis, nor loss of excess body fat, can occur without adequate thyroid hormone, making sufficient free fatty acids available for fuel. Thyroid hormones make the body more sensitive to norepinephrine -- the neurotransmitter (chemical messenger) responsible for activating the fat burning process (thermogenesis). This means that less norepinephrine is required to utilize free fatty acids for energy -- reducing unsightly body fat stores in the process.
 
Can a Lack of Thyroid-Specific Nutrients Trigger "Borderline" Thyroid Malfunction?

Inadequate nutritional support is one of the established causes of poor thyroid health. Common sense dictates that if you indiscriminately reduce caloric consumption, in an effort to quickly shed excess body weight, you also reduce the nutritional support necessary to maintain "borderline" thyroid function.