Proteins are compounds that are made up of carbon, hydrogen, oxygen, and nitrogen which are arranged into strands of amino acids. Amino acids are commonly known as the building blocks of protein, and specific bodily functions are dependent upon how strands of amino acids are arranged.
How the Body Uses Protein
Protein is found throughout the body in hair, nails, outer layers of skin, muscle tissue, the inner structure of bones, and red blood cells. Protein is used by the body to perform many functions in the body including:
- Fighting illness and disease
- Building and repairing body tissues
- Producing enzymes
- Carrying nutrients throughout the body
- Hormone production
- Creating new cells
- Maintaining fluid balance
- Transporting oxygen throughout the body
- Source of energy
Complete vs. Incomplete Proteins
Protein quality is determined by the presence or lack of essential amino acids. Essential amino acids must come from food because the body cannot manufacture these amino acids on its own. High-quality proteins, which are derived from animal sources, are considered complete proteins because animal proteins contain ample amounts of all the essential amino acids needed for the body to function properly and are absorbed more efficiently by the body. Sources of complete proteins include meat, fish, poultry, eggs, milk, and cheese.
Low-quality proteins are derived from plant sources and are incomplete proteins because they are missing one or more of the essential amino acids. Sources of incomplete proteins include grains, fruits, vegetables, beans, nuts and seeds. Even though these foods are considered incomplete proteins, they still have many health benefits because they are good sources of complex carbohydrates and fiber. Their quality can be improved either by pairing them with a complete protein in a meal or eating other complete proteins throughout the day.
Recommended Daily Intake of Protein
According to the American College of Sports Medicine, protein should make up 12 to 15 percent of total calories, and how many grams per day that should be consumed is based on body weight (in kilograms):
Infants: 2.2 grams per kg of body weight
Children: 1.0 to 1.6 grams per kg of body weight
Average Adults: 0.8 grams per kg of body weight
Athletic Adults: 1.5 to 2.0 grams per kg of body weight
Those adults who are endurance athletes have a slightly higher requirement than those who are strength athletes.
Common sources of high-quality proteins include: tuna canned in water, roasted chicken breast, roasted turkey breast, baked salmon, broiled halibut, beef steak, peanut butter, yogurt, and cheddar cheese. Those who are vegetarian may look to tofu, nuts, seeds, lentils, and soy foods to meet adequate daily protein intake.
Sources:
American College of Sports Medicine. (2007). ACSM's Resources for the Personal Trainer, Second Edition. Baltimore: Lippincott Williams & Wilkins.
Bauer, Joy. (2005). Total Nutrition. New York: Penguin Group.
Jennifer Murray - Jennifer Murray is a freelance writer specializing in nutrition, weight loss and fitness.
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