Hi, I have had an underactive thyroid for fourteen years and been on Levothyroxine for all of that time. Even on the levothyroxine I still have very low energy. I have tried every diet going, and managed to lose a few lbs on WW and SW, although it was very slowly at half a pound a week. I have just discovered the 5 2 diet and I love it. I have only been doing this for two weeks, but I have lost 4.5lb in the two weeks, eating 500 calories on a Monday and Thursday and on the other five days, I have not counted calories at all, just ate what I wanted. I feel much more energetic, and can even stay awake after 9pm! just wondered if anyone else had tried this diet, and did it help in the long term? I am really enjoying this way of eating and would like it to be a new way of life, just hoping that it is okay with underactive thyroid. Many thanks in advance.