Personal trainers, fitness magazines and websites have different opinions on what is the best pre-workout meal. Your personal trainer may suggest eating protein to build muscle, but your marathon runner friend may tell you to eat carbohydrates for energy. Other people think that working out on an empty stomach is the best way to burn fat stores; however, this approach will only be successful if you are working out at a low intensity, such as walking, for less than 30 minutes. If you are planning to perform high-intensity aerobic activity or weight train for more than 45 minutes, you may consider eating a high carbohydrate, low fat, low fiber meal with some protein.