Proteins are often called the building blocks of life. In fact, the very word "protein" implies their importance in the body: it is a Greek word meaning "first place." Approximately fifty percent of the dry weight in animal cells is comprised of protein (Campbell 71). They play a roll in almost everything the body does and "are used for support, storage, transport of other substances, signaling from one part of the organism to another, movement, and defense against foreign substances." (Campbell 71). Proteins are essential to the proper functioning of every organism known to man.
The human genetic code holds the instructions for the making of over ten thousand different types of proteins; all with specific purposes. Additionally, "Proteins are the most structurally sophisticated molecules known." (Campbell 71). In comparison to other molecules, proteins are enormous and come in nearly every shape imaginable. However, despite their variety and size, proteins are simply polymers made up of only twenty different amino acids. What makes one protein different from another has to do with the ordering of these amino acids and the shapes that they form. "By varying the numbers of different amino acids and their sequences, the body creates proteins of skin, blood, muscle, hair, bone, and nails, as well as enzymes, the catalysts that speed up chemical reactions of cells." (Ronzio 539).
About sixteen percent of protein is nitrogen (Ronzio 539). Accordingly, a rough estimate of protein content in food can be calculated by measuring the amount of nitrogen in that food. What the body generally gets out of this food is not a full protein itself -- that is broken down during digestion -- but the amino acid ingredients to build a protein. "Digesting dietary proteins supplies essential amino acids that cannot be made in adequate amounts by the body." (Ronzio 540). The body's DNA holds the information necessary to build any given protein, and the dietary amino acids are grabbed by biological processes to make-up the protein that is being coded for.
If an individual ingests a surplus of amino acids -- more than the body requires -- they are not converted directly into proteins, but instead, can be burned off as energy or stored as fat. So, it would seem from a biological standpoint that the amount of protein, in the form of food, that is taken in by the body should be proportional to the amino acid requirements for that person. However, "Most Americans eat more than enough protein to meet their amino acid needs." (Ronzio 540).
In accordance with the observation that proteins are large and complex molecules it should not be surprising that breaking them down to their amino acid components, via digestion, is a costly endeavor in terms of energy. "Protein digestion normally begins in the stomach where the strong acid (hydrochloric acid) unfolds protein in food, rendering it more accessible to attack by the digestive enzymes of the stomach. The initial phase of protein digestion yields fragments called peptides, rather than individual amino acids." (Ronzio 540). Further on in the digestive process, the pancreas and then the intestines continue to assault the peptides until, finally, individual amino acids are freed and released into the bloodstream.
Each of the aforementioned chemical processes require energy, which ultimately detracts from the net amount of energy acquired from the food. This is probably why, through their evolutionary history, humans have developed a taste for cooked forms of protein. "Cooking foods denatures and partially breaks down proteins, making them more accessible to digestive proteins." (Ronzio 540). By cooking our foods, we have increased the net amount of energy that can be freed from them.
Over the course of any given day the proteins that are in place and allow our bodies to function eventually get worn out and degrade. This is the underlying premise for the necessity of including protein in a diet: these degraded proteins need to be rebuilt and replaced. "A steady input of essential amino acids is therefore required even when the body is at a stable weight. The recommended dietary allowance (RDA) of .75 g protein per kilogram of body weight for adults was based upon long-term and short-term studies of humans." (Ronzio 541). So, for example, a 174 pound male requires a protein intake of 63 grams daily. Obviously, this rate is different for children because they require more protein to support their rapid growth. This RDA has been established as what the average adult should ingest each day.
Yet, when individuals attempt to maximize their physical capabilities, may times they try to alter the diets recommended for average adults because they consider themselves atypical. "Historically, many athletes believed that consuming...
References Elliot, D.L., Moe, E.L., Goldberg, L., Defrancesco, C.A., Durham, M.B., & Hix-Small, H. (2006). Definition and Outcome of a Curriculum to Prevent Disordered Eating and Body Shaping Drug Use. Journal of School Health, 76(2), 67+. Retrieved February 15, 2009, from Questia database: http://www.questia.com/PM.qst?a=o&d=5028537762 Maletto, Pete. (2008, October 1). Sports nutrition: past, present and future: in order to understand where this market is headed it's important to know where it's been. Nutraceuticals
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