Keep in mind that the duration and intensity of your activity will dictate how often and what you should eat and drink. For example, you'll need more energy from food to run a marathon than to walk around the block.

When it comes to eating and exercise, everyone is different. So pay attention to how you feel during your workout and to your overall performance. Let your experience guide you on which pre- and post-exercise eating habits work best for you. Consider keeping a journal to monitor how your body reacts to meals and snacks so that you can tweak your diet for optimal performance.

Source: http://www.mayoclinic.org/healthy-living/fitness/in-depth/exercise/art-20045506/