Animal products are excellent sources of protein.
Protein is a critical component of all living cells and serves many biological and chemical roles in the body. The manufacture of red blood cells, collagen, enzymes, hormones and antibodies requires protein. The body needs protein to generate new cells, transport molecules and maintain fluid, chemical and electrolyte balance. Protein is also a source of energy, providing 4 calories per gram. Deficiencies can lead to muscle wasting, poor immune function, fatigue and altered body chemistry.
Amino acids are the building blocks of protein. Twenty different amino acids form protein, each with a unique biological function. Essential amino acids cannot be produced in the body and must be supplied through food. Complete proteins, also termed high-quality proteins, are present in the foods that contain all the essential amino acids. Incomplete proteins contain only some of the essential amino acids and can be combined with other foods to create complete protein. Protein should comprise 10 to 30 percent of total calorie intake, with an average of two to three servings a day.
Meat, Eggs and Dairy
Animal products such as beef, poultry, fish, eggs and dairy are complete proteins. One egg, 2 egg whites and one ounce of meat, fish, poultry and cheese supply 7 grams of protein. A typical 3-ounce serving has 21 grams of protein. Milk and yogurt supply 8 to 11 grams of protein per cup. Meats are also rich in iron, B vitamins, zinc with dairy products offering additional calcium and vitamin D. A healthy eating plan should emphasis leaner meats and low-fat or fat-free dairy products.
Plant foods are incomplete lean proteins that provide additional vitamins, nutrients and fiber. Legumes such as lentils, peas, black, kidney and pinto beans along with soy products such as tofu offer 9 grams of protein per 1/2-cup serving. Two tablespoons of peanut butter, nuts or seeds average 7 grams of protein. Legumes are also rich in most B-complex vitamins, iron and magnesium, and contain little to no fat, cholesterol, sugar or sodium.
Other Plant Foods
Grain foods including rice, pasta, cereal, whole-grain breads and cereals contain on average 3 grams of protein per serving. When combined with plant proteins and dairy products, grains form a complete protein. Examples are rice and beans, cereal and milk and peanut butter on whole-grain bread. Vegetables contain a small amount of protein. Fruits have none, but this food group is an excellent source of vitamins A, C and K, plus folate, potassium and iron.