Your body burns fuel of some sort all day long for energy. It doesn't matter if you feed it properly or not, your body is still going to use something for fuel all throughout the day. What your body uses as fuel determines how you look (and feel for that matter). If the body is not fed properly, given the proper macro nutrients it needs, it can burn muscle for fuel which then slows the metabolism. So its important that you feed your body properly all throughout the day if you want to develop and keep your body looking its best.
It's also just as important to understand that a particular kind of exercise or workout also requires the proper kind of nutrition for fuel. You should know by now from previous articles that muscle is the absolute key to developing and keeping a fast metabolism (and reducing your body fat). So its important that you give your muscles the proper kind of fuel depending on what type of exercise you are doing.
Without going into a ton of detail, you basically have fast twitch muscle fibers and slow twitch muscle fibers. Slow twitch muscle fibers contract more slowly but they can hold their contractions for long periods of time without fatiguing (think cardio or aerobic activity). Slow twitch fibers get most of their fuel/energy from burning fat, a process that requires oxygen. Fast twitch muscle fibers are different. They contract rapidly but fatigue more easily (think weight training or resistance training). Their fuel/energy comes from burning glycogen (carbohydrates).
So you can see that it is more important to do cardiovascular training when carbohydrate stores are very low (so that the favorite energy source of body fat can be used for its fuel). The two best times to do cardio would be first thing in the morning, immediately upon rising and before eating, when carb stores are very low...or immediately after a resistance training session (again, when carb stores are very low).
And obviously, since fast twitch muscle exercise/resistance training likes to use carbs for fuel, it is important to do resistance training when you have carb stores available. So to sum it all up, eat some starchy complex carbs to fuel your resistance training workouts, but try to do your cardiovascular workouts with little or no carb stores present.