This holds true for me 100%. I was eating really well, at least a gallon of water a day, salad for lunch every day, fresh fruit, little to no dairy/sugar/junk, and my skin was looking good. Then I went on 2 really bad junk food binges in the last few months...fast food, soda, candy, chips, ice cream, you name it. I had a horrible breakout each time. Then when I got back on track, and ate healthy again my skin improved.
Everyone reacts differently, but for me it's obvious that when I put junk in my body, it comes out my skin.