Your body needs the proper type of fuel to build and maintain muscle mass when you strength train. According to the 2010 Dietary Guidelines for Americans, an active woman needs 2,200 to 2,400 calories a day, depending on age, while a man needs 2,800 to 3,000 calories a day. However, the types of foods that make up those calories matter, too.
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Importance of Protein
Out of the three macronutrients -- fat, carbohydrates and protein -- protein plays the biggest role in building and maintaining muscle mass. Recreational exercisers who lift weights need about 0.36 gram of protein per pound of body weight, while athletes looking to maintain muscle mass need 0.53 to 0.63 gram per pound of body weight. Athletes trying to build mass need 0.68 to 0.81 gram per pound of body weight. Good sources of protein include low-fat or fat-free dairy products, lean proteins such as chicken or fish, vegetarian proteins such as quinoa or beans, and nuts or nut butters.
Carbohydrates and Fat
Your body can't live on protein alone, so fill out your diet with complex carbohydrates and healthy fats. Eat Right recommends around 2.3 to 3.6 grams of carbohydrates per pound of body weight; choose whole-grain sources and vegetables. Your body also needs healthy sources of fat such as fish, nuts, nut oils and seeds. Aim to eat about 20 to 35 percent of your calories from these fats.