Guys I can only talk about this from personal experience, my own and my athletes.
I use the 5:2 diet when trying to lose weight when training and trying not to ruin my training. The 5:2 diet for anyone who has not heard of it, is 2 days a week 600 calories on your fasting day and no real restrictions on other days.
I split the 2 days up, so I do Monday, as I’m normally sure I have eaten and drunk to well over the weekend and normally Thursday, as Friday tends to be a lighter day, before weekend training. On these days I tend to follow the recipes in Michael Mosley’s books, just to make it simple.
The three things I get out of the diet are, not having to count calories every day, better hydration on the days I do the diet (as I drink a lot to keep my stomach full) and weight lose, normally around a kg (2.2lb) a week.
Once I reach my target, whether 66kg for cycling or 68kg for triathlon then I go to either none or one day, depending on the sort of week.
B