notspaghetti I found for the 5:2 to work I had to be circumspect about how much I ate on non-fast days. I tried to stay around 1200 calories.
I tend to feel, at the end of day that the best diet is the one that suits you best and from Day 1, I felt comfortable on the 5:2.
However there have been unexpected side advantages. I have had far more control over my eating than I had before I went on it, which is a mental control rather than just eating less control. I can now look at a table of food and be indifferent whether I eat or not, I can hold a plate beside the food and just not bother to put food on it.
To be fair I never really had a weight problem until the menopause. I think the weight gain was mainly hormonal. But 5:2 was effective post menopause when everything else (calorie counting, and, briefly, the Atkins Diet - now that diet actively made me ill) was ineffective.