It should take into consideration the intended duration of the exercise, the type of exercise, for example, if it is a weight-training workout or does it consist only of cardiovascular work.
As far as pre-workout eating, the appropriate choices would be foods low on the glycemic index (GI). These foods provide sustained and prolonged release of glucose into the bloodstream.
Foods that are low on the glycemic index will keep carbohydrate levels elevated throughout your workout. They will also minimise insulin surges and this is important because high insulin levels and exercise in combination can lead to low blood sugar and possibly hypoglycemia.
Apples, oranges and lentils are example of good pre-workout snacks.
For endurance athletes, in days leading up to events, for example a marathon, they often engage in carbohydrate loading. This is to ensure that their muscles’ glycogen stores are maximised. When glycogen in the muscles is insufficient, muscles become excessively fatigued and the athlete’s performance and ability to last will be less than optimal.
Foods that are high on the GI are foods that will cause more rapid entry of glucose into the bloodstream. As such, these are good to have post exercise because they will help your body and muscles to recover and refuel more quickly.
Pasta and baked potatoes are good options. You may be tempted to put something fatty, such as butter on these items. Please don’t, as fat will slow down the release of sugar into the bloodstream. Bananas and low-fat yogurt are good choices because they contain sodium, calcium and potassium, which are necessary minerals in the recovery process.
For a bodybuilder whose body would require more protein after a workout than, say, someone who simply uses a treadmill, a shake containing whey protein would be a primary option for a post-workout meal.
Take the time to make sure that what you put in before undertaking the workout will benefit you and not hinder you, and that what you put in afterwards will help you to recover from the rigour your body underwent and will not undo your hard work.