You need to eat before and after you exercise; it is necessary to eat before workout in order to have a better performance, and also you need to eat post workout so you can recover faster.   Timing is crucial, so take advantage of the following advices:

Eating before workout:

You should try to eat something, carbohydrate focused, 90 to 60 minutes before you exercise; this way you will not be too full, you will elevate your blood sugar, and you will have energy to perform better.   Water should always be part of your meals, you should also hydrate during and after workout.

I usually eat a bowl of oatmeal with low fat milk, plus few raspberries, 90 minutes before my exercise; this gives me the right energy to perform well and it won’t upset my stomach.  It depends on preferences, some people like to eat fruits like berries, bananas, kiwi; others prefer to eat cereal bars, or drink a glass of juice, etc; it all depends on how well your body reacts to food.   What is recommended is to give at least one hour of digesting time for every 200 to 300 calories consumed.  

There are two common mistakes: some people don’t eat anything at all before exercising; this will make them feel weaker and tired, since blood sugar level is low. I recommend, first thing in the morning to consume a meal, carbohydrate focus (carbohydrates have a direct effect on blood sugar), before your workout, which would elevate your blood sugar and help you perform well during your workout.  Gels are also effective for this purpose.  The second mistake is eating too much before training; in this scenario the person will be too full to perform.  If our stomach has a lot of food, then it will take longer for it to get empty.

On a race day, the meal should be more substantial; and should be consumed at least 2 to 3 hours  (500 to 900 calories) before the race starts.

Eating after workout:

It is recommended to eat post exercise in order to better recover.   The longer we wait to eat something, the longer our body takes to recover.   Most people refuel with low fat chocolate milk, which works very well, since it has sugar and protein.  We need sugar to recover our blood sugar level.   Protein shakes are recommended after strength training to help build muscle tissue; it is always better to drink it 15 to 30 minutes post workout.

Enjoy and work hard!