If it suits you, then it suits you. My sister likes it and it works worked well for her, no thyroid problems there though. It seems to me as if you have light days, not to be confused with no eat days and normal days and over the course of say a week you have a deficit which should give a weight loss. Thyroid playing properly please. All anyone can do is what suits them. My only thought is, will this form a regular structure for you when you start to maintain? You should be no more at risk of not achieving a good balanced diet than anyone else trying to reduce by a regular calorie intake. I think most criticism comes from those who do not see this as a sustainable way of life.

Go with what works for you

This is my third week of eating 5:2 and each week I have seen the numbers on the scale move down. I had a Tirosint dosage change a couple of months ago as I was starting to go hypo again. Prior to 5:2, I had been on WW for 6 months and played with the same 5 pounds the entire time. 5:2 seems to be getting my weight loss moving again. There is a 5:2 board that may be able to provide some additional information.

Whatever you decide, good luck!