problem with 5:2, is it will drop your overall calorie intake over a 7 day period but it won't address poor dietary habits, so mate loses weight when he does it but gains it back when he stops, this is of course due to no change in the normal eating days which for him consist of beer, wine and lots of roast like meals, high fat pasta etc, he's doomed to calorie overload.
so what's going to work is a reduction overall in your calorie intake everyday .... and of course remove alcohol, processed meats and processed foods generally. we all know this replace with complex carbs, lean meats, fruit and veg, water.
so initially I looked at my overall calorie requirement, and you have 3 options put on weight, lose and maintain. For me I want to lose then maintain whilst training up and keeping fit. You'd think the 'lose' part of your intake would mean loss of energy, nope it hasn't, as I think body is now burning fat as fuel source so not a bad thing.
have to remember that Rome wasn't built in a day so it's going to take time.