Going to the gym and pounding the weights six days a week can give you negative affects unless you feed your muscles with the food it needs to rebuild.

Protein is made of Amino acids and your body needs protein to build muscles. If you are really serious about building muscle you will need to take in 1 2 grams of protein for every pound of weight. For example I weigh 198 pounds (90kg) so I need to take 198 to 396 grams of protein a day to really build muscle mass quickly and efficiently.

Naturally your body can only take in about 40 grams of protein in one meal, any more will result in the excess becoming a waste product. There are many different types of protein like Whey, Egg, Soy and Casein. These types of protein take different times to be digested by the body, for example

Whey Takes only about 30 mins to be digested by the body

Egg Takes between 1.5 to 3 hours to be digested

Casein Takes between 2 to 7 hours to be digested

Soy Is a good overall protein that is perfect for vegetarians as it is derived from plants.

Casein (a milk protein) is normally taken at night before bed so you have the benefit of protein being digested in the body while you sleep.

Muscle building is not a science but eating correctly will give you better results.