I lost no weight on the scales and was hyperthyroid for a year. I had severe insulin resistance (fat storing mode!) already but when I was hyperthyroid this condition worsened and I also develeped pre diabetes (impaired glucose intolerance).
Due to fast metabolism, I also depleted my stomach acid, my tooth enamel cracked off in various places, muscle atrophy (the body eating away my muscle and plenty of it!) and just near the end of that year a small dip of fat (looked very weird lol) showed up on the side of my abdomen (finally the body somehow managed to accessed a small section of fat). It's very difficult for the body to access the fat stores when insulin is high. VERY difficult.