funny that's part of the problem isn't it! the latest diet always has the 'best' theories and they change all the time. The truth is there probably is no perfect healthy diet and each of us will do better on different food and that too will change during different points in our lives. The 5:2 makes great claims for health and obviously works, weight control wise, for many, but there are also studies that show, for women in particular, that it can actually have negative impact on health, especially wrt fertility. The tests they shout about were done mostly on men, so it's early days with that one.
So what to eat...for me, it seems clear that the traditional food pyramid, with carbs at the bottom, is wrong. I think there should be a much more even split between the ratio of carbs, fat and protein we consume. Other than that, if I gave any rules - to follow 80% of the time - they would be to avoid sugar, white and processed carbs and anything containing trans fats. As much as possible eat whole, unprocessed foods, preferably organic. Experiment with how you feel if, say, you give up dairy for a week or two, then maybe try the same with wheat. You may feel better, you may feel worse, you may feel worse but decide that you just miss yoghurt/toast so much it's not worth giving up 
, but then you know to have such things as an occasional thing, rather than a staple item. I think if we learn to tune into how our body feels (not necessarily looks) and listen to it then long term you will end up eating a healthy diet and your weight will find its healthy balance. You can also give yourself the freedom to have a bit of chocolate every day or a cake once a week. Hopefully you will end up seeing food as a friend rather than something to battle with? This is all notwithstanding more psychological issues of course, where someone is comfort/binge eating for example, that would usually indicate other issues in their life that would need to be looked at - boredom, depression, relationship issues etc - separately .