A Protein is any of a group of complex organic macromolecules that contain carbon, hydrogen, oxygen, nitrogen, and usually sulfur and are composed of one or more chains of amino acids. Proteins are fundamental components of all living cells and include many substances, such as enzymes, hormones, and antibodies, that are necessary for the proper functioning of an organism.

Protein is an essential nutrient whose name comes from the Greek word "protos," which means "first." To visualize a molecule of protein, think of a very long chain with links. These links represent amino acids, the building blocks of protein, which are essential for cell regulation, growth, and repair.

Most of us recognize the term protein in a nutritional context as referring to a class of foods that includes meats, dairy products, eggs, and other items. Certainly, proteins are an important part of nutrition, and obtaining complete proteins in one's diet is essential to the proper functioning of the body. But the significance of proteins extends far beyond the dining table.

Key Functions of Protein

Protein consists of compounds of twenty amino acids. Twelve of these are the nonessential amino acids that the body can manufacture for itself. The eight essential amino acids, those the body cannot manufacture, are isoleucine, leucine, phenylalanine, valine, threonine, methionine, tryptophan, and lysine. Proteins are further broken down into three types: animal, lacto and vegetable.

* The body uses protein to build new cells, maintain tissues and regulate cell function.
* About half of the protein consumed daily is converted into enzymes, the specialized "worker proteins" that regulate the speed of biological reactions in your body and permit it to perform functions such as digesting food and assembling or dividing molecules to make new cells and chemical substances. To perform these functions, enzymes often need specific vitamins and minerals.

Food Sources of Protein

Meat used to be considered an indispensable source of protein because it contains all of the essential amino acids. Nutritionally speaking a protein is considered high or low quality depending on how many of the needed amino acids it contains. However by properly combining different sources of vegetable protein one can create a "complete" protein.

Food can be divided into high protein or low protein. High protein foods are those that contain at least 10% protein by volume. Meat is a high protein food but the problem is that the body cannot digest large amounts of meat at one time. Also meat by itself does not easily pass through the digestive tract. Even when eating meat it is still a good idea to consume a larger amount of nonstarch vegetables with it for better elimination.

It's important to pay attention to what comes along with the protein in your food choices. Vegetable sources of protein, such as beans, nuts, and whole grains, are excellent choices, and they offer healthy fiber, vitamins, and minerals; nuts are also a great source of healthy fat. The best animal protein choices are fish and poultry. If you are partial to red meat, such as beef, pork, or lamb, stick with the leanest cuts, choose moderate portion sizes, and make it only an occasional part of your diet: A major report on cancer prevention recommends consuming less than 18 ounces a week of red meat and avoiding processed meats (such as hot dogs, bacon, or ham) to lower the risk of colon cancer.

Daily Usage of Protein

The Institute of Medicine recommends that adults get a minimum of 0.8 grams of protein for every kilogram of body weight per day to keep from slowly breaking down their own tissues. That's just about 8 grams of protein for every 20 pounds of body weight. Beyond that, there's relatively little solid information on the ideal amount of protein in the diet, a healthy target for calories contributed by protein, or the best kinds of protein.

It is possible to consume too much protein. The amount of protein needed for good health varies.

* As you grow older, new proteins are synthesized less efficiently, and muscle mass (protein tissue) diminishes while fat content stays the same or rises. This is why muscle seems to "turn to fat" in old age.
* Infants, adolescents, pregnant women, individuals with injuries, and athletes may often require more protein on a daily basis.

Nutritional Safety

Several medical conditions make it difficult for people to digest and process proteins properly. As a result, waste products build up in different parts of the body. Check with your physician for individual safety concerns you may have.

The most important thing to remember in all of this is that digestion will always result in waste products and the more complete digestion is the fewer wastes produced. Since the body cannot utilize large amounts of protein and has difficulty digesting large amounts of animal protein digestibility becomes the most important factor.

My next article entitled "The Function of Fats in our Life" will examine the role of fats in good nutrition.