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Proteins are substances made from combinations of amino acids. Amino acids are chemical compounds containing nitrogen, carbon, oxygen, and hydrogen in distinct arrangements. Amino acids usually contain sulfur and sometimes phosphorous, iron, or iodine.
Proteins are essential to life: they are the major source of building materials for muscle, blood, skin, hair, nails, enzymes, hormones, and antibodies. Proteins can serve as an energy and heat source for the body and are needed for proper elimination of waste materials through urine.
Proteins are broken down into amino acids by enzymes in the stomach and small intestine. Amino acids are then transported to the liver and other organs where they are resynthesized into proteins the body can use or burn as fuel. Excess protein the body cannot use and protein breakdown products are converted to urea (an ammonia compound) and excreted in the urine.
Although more than 100 different amino acids occur in nature, only 22 are needed in humans. The human body is capable of making 14 of these amino acids. Amino acids that the body makes are called nonessential because protein intake is not needed. Eight amino acids, called essential amino acids, must be obtained from dietary sources.
Essential amino acids include:
In addition to these essential amino acids infants also need arginine and histidine. Cystine and tyrosine, limited substitutes for methionine and phenylalanine respectively, are considered quasi-essential amino acids.
What foods contain protein and how much do I need?
Meat, poultry, fish, milk, eggs and cheese are considered complete sources of protein because they contain the eight essential amino acids. Nuts and legumes, including navy beans, peas, and soybeans are good sources of protein but are considered incomplete because they do not contain all 8 essential amino acids.
Vegetable combinations, such as corn and beans, do contain all essential amino acids. Although it takes a little extra work determining vegetable combinations that provide all essential amino acids such combinations provide excellent quality protein free of fat and cholesterol.
Protein requirements are not exact. Absolute protein deficiency in developed countries is extremely rare! Protein deficiency with normal calorie intake results in "kwashiorkor" resulting in gradual health deterioration with a bloated belly appearance in children. Marismus is due to deficiency of both protein and total calories and results in a typical concentration camp appearance; deterioration is quicker than with kwashiorkor. Adults with severe protein deficiency may be very weak, lacking vigor and stamina, exhibit depression, have poor resistance to infection and delayed healing. This typically occurs in rehabilitated elderly persons who are not able to eat properly for a variety of reasons.
The typical American gets between between 35 to 70 grams of protein per day without supplementing their diets. This averages between 1/2 to 1 gram of protein per kilogram of lean body weight. A kilogram is 2.2 pounds. These levels appear more than adequate for maintaining good health. Increased supplementation is not required for the average healthy person working out to maintain overall fitness.
It is believed that persons involved in very heavy physical exertion, such as competitive athletes actively training, may require between 1 to 2 grams of protein per kilogram of lean body weight. This amount is not required for the typical person working out at the gym to maintain fitness. In persons following a relatively low fat diet obtaining more than 60 grams of protein per day may require additional planning.
As the name implies, protein powders contain protein. Virtually all current protein powders contain either soy protein or whey protein along with various minerals and flavoring agents. Despite the dozens of brands available most of these powders are supplied by several huge corporations involved in food processing. Examples include subsidiaries of Dupont and ADM (Archer-Daniels-Midland).
Soy and whey are the most common constituents of infant formulas. In fact, infant formulas and protein powder supplements have many things in common. The overall quality of infant formula is more consistent and uniform than supplement powders.
One will frequently find advertisements touting individual amino acids as being the key to greater strength, size or stamina. There is no evidence that high intake of any single amino acid helps with anything. We recommend saving your money. People get all the amino acids they need by eating complete proteins and proper combinations of vegetable proteins.
Protein and calorie supplements, such as Ensure, that used to be used primarily by healthcare professionals in selected patients are even being marketed directly to the public. These products are high in protein, fats and carbohydrates and were initially intended for malnourished elderly patients and recuperating burn victims requiring temporary high calorie and protein diets. Otherwise healthy persons frequently using these products are likely to gain unintended weight.
Extremely high amounts of protein (in excess of 2.5 grams per kilogram a day) may be harmful to both kidneys and liver over a period of time. There is evidence that excessively high protein intake over a number of years may result in decreased kidney function and possible kidney failure in some individuals.
Even higher protein intake can be more immediately toxic because excessive acids that cannot be excreted cause undesirable changes in body functioning. Fortunately the human body has developed an effective mechanism against excessive protein intake in that people lose the desire to eat proteins when intake is too high. There appears to be no such satiety limit for carbohydrates.
Protein powders and amino acid supplements may have a place under certain circumstances for the individual who is involved in a rigorous weight training program or other highly demanding physical activity. Likewise, these products can be a useful supplement for vegetarians. [ Vegetarians avoiding milk products would not use whey supplements.]
Soy and whey protein are certainly acceptable sources of protein; however, neither source is needed in adults with normal protein intake from other sources such as vegetables and meats. Whey and soy are no better (actually not as good) than high quality meats.
Protein powders may be more convenient and as economical on a gram per gram basis as lean meats such as chicken or fish. Although they certainly do not taste as good alone they can be blended with fruits and dairy products. Quality may not be uniform. Protein in excess of what the body requires is simply excreted or converted to fuel for the body. Protein is an expensive source of calories compared to carbohydrates.
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