Yeah, its more complex than this but the basic idea is having your food intake match your exercise habits. There are lots of people who drink protein shakes, eat lots of protein, etc, but don't work out enough for it to do anything, and they end up gaining fat because their intake is way over the top for what they need. Like I said I work out 5 days a week, but if I have a light week I won't drink protein shakes. In my opinion they aren't necessary unless doing heavy lifting workouts or cross-fit where muscle recovery determines performance in the next workout. Getting enough rest is just as important.