Nutrition Facts - Diet And Nutrition - Free Diet Plans

Proteins

July 21st, 2005

How Important is Protein?

Protein is necessary for the growth, maintenance, and repair of every cell in the body. It is present in countless forms throughout the body—as part of enzymes, hormones, antibodies, oxygen carriers, bones, muscle, hair, and skin, to name a few. Unlike the fuel­providing carbohydrates, proteins are the building blocks that provide structure and perform vital functions. However, when needed, proteins can break down to provide energy—4 calories per gram.

Small units called amino acids unite to form the structure of proteins. Altogether there are 20 common amino acids. They mix and match in thousands of different combinations to make up specific proteins. Since your body cannot manufacture nine of these amino acids, you must get them from your diet. Proteins in your food provide them, with the most concentrated sources coming from animal products—meat, chicken, fish, dairy products, and eggs. However, it is also possible to get protein from plants such as beans, nuts, and grains. In fact, most of the people in the world get their protein from vegetable sources for either cultural or economic reasons.

Animal versus Plant Proteins

Proteins from meat, poultry, fish, and dairy foods are called complete proteins because they furnish all the amino acids needed for growth. Most plant proteins, on the other hand, are incomplete: Except for the soy bean, no single plant provides all nine essential amino acids. (Soy, though complete, is still considered inferior to animal proteins.) You can, however, meet your daily requirements by consuming a variety of plant proteins over the course of each day. For example, the amino acids from beans taken at one meal can complement the amino acids from rice eaten at another meal that day. Other examples are peanut butter and wheat bread, or macaroni and cheese. (In the latter case, the essential amino acids from the animal product, cheese, allow the body to better use the amino acids in the macaroni.)

Dietary protein deficiencies in this country are relatively rare. When they do occur, they are usually the result of a disease that causes loss of appetite or loss of large amounts of protein from the body.

Excess dietary protein is a much more common problem. Government surveys estimate that the average American consumes about 100 grams of protein per day—almost twice the recommended daily allowance (RDA) of 50 grams for women and 63 grams for men. Excess protein taxes the body physiologically. Once it’s digested and absorbed, end products of protein metabolism are excreted in the urine; so any excess places extra burden on the kidneys. Nor does excess protein build muscles. It is either burned as energy or stored—not as muscle, but as fat. Many athletes, particularly those involved in strength training, believe that to build muscle you need more protein. In fact, Americans already get more than enough; and exercise, not extra protein, is the only way to increase muscle size and strength.

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