There are loads of theories on how to fuel your body before and after a workout. Below are the basics on how to do so. They are not gospel but a good starting point which can be minupulated to suit your own requiements.
Eating carbs before a workout and extra protein afterward provides the basic materials that your body needs for adapting to the demands of your chosen activity. Pre workout carbohydrates help ensure that your body has what it needs for rising to the challenge, and making the most of your workout. Post workout dietary protein provides aids in recovery processes in between each workout session.
Glucose is the primary fuel for all the cells in your body. Ingesting carbohydrates before a workout triggers the insulin response that your body needs to use glucose for energy. Your body releases insulin when you eat carbohydrates, and insulin carries glucose into the cells. Ingesting carbohydrates before a workout also replenishes glycogen stores, which provides muscle energy during your workout. The average adult body can store up to 500 grams of carbohydrates in the form of blood glucose and glycogen.
In addition to your continuing need for carbohydrates to fuel your body, you need to add extra dietary protein after a workout to repair cells and make new ones. Your body breaks down the protein that you eat into amino acids, which are used for repairing tissue damage that occurs during your workout. Workouts deplete cellular catalysis, which drive life-sustaining processes in your cells.
Your muscles would not work without cellular catalysts, and ingesting protein after your workout replenishes these essential components. Ingesting protein after your workout also supplies amino acids that you need for building new muscle tissue. If you don’t eat enough protein and carbohydrates after your workout, you can lose muscle tissue, because your body breaks down its own muscle proteins unless you provide sufficient nutrients in your diet.