There's not a "healthiest food". You just need to work out how many calories you can eat in a day, depending on your weight, measurements, and what you're willing to get (maybe muscle, maybe lose fat...)
Then (what I do) is to use a application called MyFitnessPal and record what you eat in a day so you know exactly whether you are eating more than you should or not. The app also tells you about macronutrients such as protein and carbohydrates, which is really good as well.
However, try to avoid added sugar foods like crisps, biscuits, fizzy drinks...
I'm free to be your motivation buddy if u want. Just let me know and we'll get to know each other.