Before going to the gym, about 2-3 hours before, you can eat a big meal. The meal should contain proteins and carbohydrates. For example you could eat a barbequed steak with rice and a salad. Also a half an hour before going to the gym you can eat a cereal bar or a protein bar. That way you are going to handle the workout better because you body has the necessary resources at his disposal.
Do not forget to drink lots and lots of water during the physical exercises. You have to replenish all the liquids you are losing by sweating during the workout. Keeping yourself hydrated. That way your work out will benefit you more and you will avoid suffering injuries to your internal organs. Your body produces a lot of toxic waste that is eliminated by sweat and other bodily functions. Water is the key component thru which the body can eliminate a lot of those toxins so that they don’t accumulate in time. Also the workout itself makes your body accelerate the production of some natural body toxins that have to be eliminated. And water is the key component.
If before the workout it is recommended for you to eat proteins and carbohydrates, after the workout you can eat a salad made out of fresh vegetables, chesses, yogurt. Something light and refreshing is recommended. After the workout you body goes in repair mode. If you gobble down a slow digesting meal a lot of the energy will go towards digesting the meal and not repairing the muscles. And muscle repair is what makes your muscle mass grow and get stronger.