Your thyroid is that butterfly shaped organ sitting at the front of your neck. Your thyroid is responsible for your body temperature control, hormonal system, metabolism and that affects the amount of fats you keep.
The most common pathology test for thyroid is the thyroid stimulating hormone. Your thyroid stimulating hormone is secreted by the hypothalamus, that sits in the brain. When your thyroid stimulating hormone is high, you are working hard to produce thyroid hormones, which means the thyroid is underactive, not the reverse, as many might think!
An underactive thyroid makes metabolism sluggish, hence the accumulation of body fats. The person also feels tired, may have persistent elevated cholesterol, experience cold hands and feet, have intolerance to cold, suffer from constipation, feel depressed, and have dry skin and suffer hair loss. But, the thyroid stimulating hormone is not the only test for thyroid health! More often than not, thyroid problems arise from the conversion of T4 to T3. Your thyroid produces T4, and T4 is converted to T3.
You can have perfectly “normal” TSH and still have a problem with the thyroid if your body if producing a lot of reverse hormones or if there is excess antibodies, i.e. a situation of autoimmunity (you attack your thyroid cells, hence destroying it).