Proteins perform highly specialized functions in our body. They do most of the work in cells and are required for the structure, function, and regulation of the body’s tissues and organs. Basically, proteins are long chains of amino acids.
Essential and non-essential amino acids
There are twenty different amino acids, and these amino acids can be combined into many different types of proteins. Nine of these amino acids the human body either cannot make at all or cannot make in sufficient quantity to meet its needs.
These nine amino acids are called essential amino acids because they must come from food.
The non-essential amino acids are just as important as the essential amino acids, but the body can make them from other amino acids. However, sometimes a non-essential amino acid can become conditionally essential if , for example, the diet doesn’t provide enough of the amino acid it is made from, or if the body cannot make the conversion.
Proteins have numerous functions in the body. Some proteins function as building materials for body structures. The structure of all body cells require protein.
Protein is used to build skin, body tissues, muscles, hair, and fingernails. Protein collagen forms the matrix for bones, teeth, ligaments and tendons. Protein collagen also repairs tissues.
Proteins function as enzymes.
Enzymes are smaller proteins that catalyze or speed up chemical reactions. Enzymes are responsible for most of the chemical reactions in body cells. Enzymes often need vitamins or minerals for activation.
About half of the protein we eat every day is used to make new enzymes. Some hormones are proteins. Hormones act like messengers turning on and off body processes in response to the body’s needs. Some hormones that are protein include insulin, thyroid hormone, histamine, adrenaline, and serotonin.
Proteins are also carriers or transporters.
Some carriers help nutrients cross cell walls, others are in the body fluids and carry nutrients and other compounds throughout the body, for example the protein hemoglobin carries oxygen from the lungs to the body cells. Proteins help maintain the body’s fluid and electrolyte balance.
By accepting and releasing hydrogen proteins act like buffers to help maintain the body’s acid-base balance. Antibodies are proteins that function to defend the body against disease. Proteins also function in blood clotting and vision, wound healing.
Even though protein has vital functions in the body, if glucose is limited the body can metabolize amino acids for energy. One gram of protein provides 4 calories. The body will break down body tissues in order to provide the amino acids for energy, which can lead to wasting of lean body tissue.
The body is constantly breaking down and repairing body tissues, making hormones, enzymes and other body protein compounds. Therefore, the protein must be replaced by new protein.
For your body to use the proteins from the foods you eat, it must do two things. First, the body breaks down the proteins in the digestion process to amino acids. The cells lining our digestive tract absorb single amino acids or small chains of two or three amino acids, which are broken down in the intestinal wall cells.
Second, the cells in the body take up those amino acids and rearrange them to build the body proteins it needs. One common misconception is to take enzyme supplements.
Enzymes are proteins and the digestive enzymes will breakdown the enzyme into single amino acids, and it will not loner be an enzyme. Then the body will use these amino acids to build the proteins it needs, not necessarily will the original enzyme be reformed by the body.
We get dietary proteins from both animal and plant foods. Proteins from animal sources are called complete proteins, because they contain all the essential amino acids in amounts large enough to meet the body’s needs. Proteins from vegetable sources are called incomplete proteins, because they are low in one or more of the essential amino acids. Some plant proteins such as soy protein are complete.
The quality of vegetable proteins can be improved by combining different plant proteins. Combine one plant protein that is low in one amino acid, with another plant protein that is high in that amino acid complement each other.
Another way to complement a plant protein is to combine it with a small amount of animal protein. When complementary proteins are eaten together or within the course of the day all essential amino acids are provided.
Wheat and rice are low in lysine, an essential amino acid. Beans are low in methionine, another essential amino acid. Since both contain reasonable amounts of the other essential amino acids, rice and beans, or peanut butter and bread complement each other to make a complete protein.
Combining either plant protein with an animal protein source such as macaroni and cheese also makes a complete protein mixture. For example, corn is low in two amino acids; lysine and tryptophane.
Combining beans or other legumes with corn adds these two amino acids to corn and makes a complete protein. Pinto beans and corn bread, beans and corn tortillas are complementary protein mixtures.
If more protein is consumed than the body needs to build or repair body tissues or to provide energy they are converted by the body into fat and stored for later use. In this process nitrogen groups are removed from the amino acids which are converted into urea and removed from the body by the kidneys.
How much protein do we need
Most Americans do not suffer from a lack of protein. The Recommended Dietary Allowance for adults for protein is 0.8 grams protein per kilogram body weight. The Dietary Guidelines for Americans recommend that about 12 to 15% of our daily calories is recommended to come from protein. Adequate protein needs can easily be met by following the Food Guide Pyramid.
For athletes and people performing other intense physical activities the protein requirements are higher.
For example, six bread, cereal, rice or pasta servings provide about 18 grams of protein; 3 vegetable servings provide 6 grams of protein; 2 milk servings provide 16 grams of protein; and 2 meat or meat alternative servings provide about 35 grams of protein. This totals to 75 grams of protein which is higher than recommendations for most people.
Many individuals limit meat and dairy foods to lower fat and cholesterol or for weight loss. However, lowering fat in the diet doesn’t mean omitting meat and dairy products. These foods are part of a well balanced diet.
Protein and amino acid supplements are promoted for a variety of reasons. Protein and amino acid supplements don’t perform miracles and they can cause harm.
For example many claims are made regarding protein or amino acid supplements building muscles; however, using muscles builds muscles, not taking supplements. Supplements are here just to help you reach your macronutrient needs, depending on the activity you are performing.