i eat clean 6 days a week and Fridays i junk out and i pay for it digestive wise- but for ME it keeps me on track.
The trick for me to transition was finding replacement whole foods for the junk i was eating. I knew i HAD TO have chocolate in my daily diet so i ditched the M&M's for hot cocoa made with vanilla almond milk, stevia and dark cocoa powder and it actually does the trick for 1,000's of calories less.
Lunch is usually a huge bowl of non fat unsweetened Greek yogurt with stevia, lots of fresh strawberries, blueberries and a small handful of walnuts and almonds and that seems to satisfy everything! So find foods that you will love and work them consistently into your diet