Whether you are training to better your athletic performance or just looking to slim down, acquiring lean muscles mass is a struggle for many of us. It would be nice if the BigMac could provide the right nutrition to attain the ripped physique of Taylor Lautner, but for most of us, it just won't work, hence America's growing obesity rate. In order for you to burn excess fat you're going to need to increase your metabolic rate, while providing the nutrients your body needs to build and maintain muscle mass.
Protein is needed to build muscles, and lack of it will result in substantial losses. You can work out all day but won't get results without eating right because of malnutrition. Some good sources of protein are lean meats (chicken, beef, turkey etc.), fish, beans, eggs, nuts, and lentils. It is also very important to eat good portions of carbohydrates, and fats as they are needed for your body's to function properly.