Clean Living is life without toxins.  Ingesting foodstuffs that hasn't had a whole heap of processing done to it before it reaches your mouth.  Receiving food in its raw state is the best way to indulge in a clean lifestyle.  Additives such as preservatives, sugars, flavourings and the like, all have toxic elements contained within them.  Some of these are processed within the body and some stay around in fat deposits after the body has dealt with them.  Now you aren't going to have a toxic system by eating a bowl of factory produced microwaved french fries.  But consistent ingesting of this type of food is going to build up levels of toxins in your system which is going to raise issues over a sustained period.