Are you sure you are eating enough? Once I went on a diet for a long time, and when I got frustrated at how long it was taking to get the last ten pounds off, I started really starving myself (about 800 calories a day). One day I started getting very chilled. It was 95 degrees outside, but I found myself shivering all the time and wearing long sleeve sweatshirs (even outdoors) to stay warm. I would walk down the street in my long sleeve winter sweatshirts and people would look at me like they were shocked. When I started reading about why I was so cold, I learned that when the body does not get enough calories, it begins to feel its survival is threatened and shuts down all functions it considers not absolutely necessary for survival. One of those functions is keeping the body warm (other than keeping its core around vital organs warm.) I don't know how this translates as far as thyroid or matters other posters have raised, but I thought I would let you know about my experience.