The studies I've seen appear to show that most people don't lash out on the unhealthy stuff on non-fast days

Not true for everyone! I have tried every diet going, including 5:2. I start off being very good and lose weight as expected. Then slowly, slowly, my "eat what you want on the non-fast days" increases until I am undoing all the good work of the fast day. My mind then becomes fixated on how to stop this - even to the point of changing 5:2 to 4:3 (which I have done at sometime). Fixation is a big problem. What happens if your fast day coincides with a special occasion where you know you will be eating. Do you skip it? Bring it forward? Shift the whole cycle back one day? Add an extra fast day to compensate? It's not long before your diet is occupying all your thoughts.

..... it's not a long dreary slog with no end in sight.

The amount of weight I need to lose means that it is, inevitably, a long dreary slog with moments of despair when I plateau out for a week or more, before restarting the weight loss. There is no end in sight. I have lost 3 stone many times, only to put 3 stone 2 pounds back on again. My weight has followed a saw-tooth upward trend. I am now on the way down again but, this time, even losing 3 stone will leave me overweight. I know I can win the battle but, inevitably, I will lose the war.

I eat very little processed food, rarely have take-aways, drink only moderately and my taste for sweet things has decreased over the years. I eat a well balanced diet - I just eat too much. In my effort to get my five-a-day, I can demolish the fruit bowl. Eating too much meat means that I have to eat too much dessert to maintain the balance. My biggest problem is comfort eating through boredom

Steve has it right, upthread. Exercise, portion control and avoiding snacking are better than fad diets.

DC