How can eating healthy be a disease at the same time? How can two object occupy the same space at the same time? IT CAN'T. We are looking at a contradictio in terminis so don't be fooled.
Of course one could argue that some people obsess over food, are too fanatical about it but that has NOTHING to do with the difference between healthy and unhealthy food.
Roughly there are 4 types of food, from 'good' to 'bad':
Now go figure which food items belong to which category, decide if you want to live healthy or not and determine your diet accordingly. Simple.