Amino Acids Introduction

Living in today’s modern society, where skinny is “in”, one cannot not ignore the high protein, low, or no-carbohydrate diets that are sweeping the nation in growing popularity. But to truly understand the reasoning behind this growing weight-loss trend, one must first realize what he/she is consuming. So, what exactly is protein?

Protein is a complex organic substance and is the building block for the majority of all of all biochemical processes taking place in the body. It’s primary responsibility lies within the formation of vital body tissues, antibodies, and the creation of important enzymes and hormones. Protein is second to only water in regards to its overall abundance and availability in our bodies. It is distinguished from the other organic substances we consume (carbohydrates and fats), by nitrogen - containing nearly 17%. With the exception of certain fluids, bile, and urine, every living cell contains protein.

Protein is a vital nutrient. It consists of polymers that form amino acids and contains the elements: Carbon, Hydrogen, Oxygen, Nitrogen, and Sulfur. Amino acids are also the end product of hydrolysis, or protein digestion. Amino acids bind together in peptide bonds to form a given protein. They can be thought of as separate train cars on a train track. Each individual car represents a different amino acid and defines the formation of a specific protein. There are 28 primary amino acids commonly referenced to define a given protein. A particular sequence of amino acids defines a given protein and translates to its action in the human body. A different chemical arrangement = different protein. [1]

Amino acids are categorized as essential or nonessential subunits of protein. Our liver produces nearly 80% of the amino acids needed for sustaining life. These amino acids are considered nonessential (dispensable) because our body manufactures these if they are not obtained from the diet. There are approximately eleven nonessential amino acids produced by our own body’s cells, including;

Nonessential Amino Acids

• Alanine
• Arginine
• Asparagine
• Aspartic Acid
• Cysteine
• Glutamic Acid
• Glutamine
• Glycine
• Proline
• Serine
• Tyrosine

Other amino acids often classified as nonessential include; Carnitine (which is derived from B-Vitamin compounds), Citrulline, Cystine (the N-acetyl from of cysteine), GABA (Gamma-Aminobutyric Acid), Glutathione, Homocysteine, Ornithine, and Taurine.

The remaining 20% of amino acids needed to build specific proteins must be obtained from diet and are defined as essential (or indispensable). In stark contrast to the nonessential form, these critical amino acids cannot be produced within the body and it is essential that our diet provides adequate supplies of these nutrients. Because of the possible inadequacies of the essential variety of amino acids, some 9 - 11 aminos may be considered essential in making up the composition of certain proteins. These amino acids include;

Essential Amino Acids

• Histidine
• Isoleucine
• Leucine
• Lysine
• Methionine
• Phenylalanine
• Threonine
• Tryptophan
• Valine

Arginine and Glutamine are nonessential amino acids that may become essential during periods of disease and/or stress (e.g. premature infancy). These two amino acids define the tenth and eleventh amino acids that may be converted for essential use, due to their varying characteristics and overall importance.

The digestion of nonessential and essential amino acids is very efficient. After ingestion, each peptide bond of amino acids defines a certain protein and its given function. The function of a given protein is often dependant upon our bodies needs at a particular moment, and will be used accordingly. This is truly an amazing metabolic process. Due to efficiency of this nutrient, we digest nearly 97% of all animal sources of protein, as well as up to 85% of protein obtained from cereals, fruits, legumes, and vegetables. The only foods that do not contain any protein in our diets are pure fats and sugars. [2]

Animal proteins are considered complete proteins. These proteins are of exceptional quality and contain all 9 essential amino acids. A recent survey indicated that nearly 65% of the consumed daily protein in the United States is of the animal variety. Vegetable products, with the exception of soybean, are considered incomplete proteins because they lack one or more essential amino acids. Vegetarians are the demographic at greatest risk for the development of a protein deficiency due to inadequate intake. Because of this, vegetarianism requires the individual to complement two incomplete proteins together to fulfill essential protein needs.

The majority of amino acids consist in two different forms; Dextro and Levo forms, commonly referred to as the D- and L-forms. These forms are consistent with each amino’s unique biochemistry. Humans benefit from the compatibility of the L-form amino acids rather than the aforementioned D-form. L-form amino acids are available for supplementation in their purest form, and are also called free-form amino acids. In this form, they are immediately ready for use via the bloodstream and do not require digestion. This may prove especially beneficial for individuals suffering from digestive disorders, or allergenic food sources. One must, however, be cautious and aware of the potentially dangerous effects of mega-dosing amino acids over a extended period of time. [3]

Because of the availability of amino acids in a balanced diet, protein deficiencies are rare. Inadequate intakes of proteins may be seen in individuals who are neglecting indispensable amino acids, or the classified essential aminos (i.e. Vegetarians). A protein deficiency can result in the reduced growth in children, muscle wasting in adults, and often times bears the accompaniment of an increased susceptibility to a myriad of diseases.

Protein deficiencies are categorized by two specific forms:

1. Maramus- defines a deficiency of both protein and energy
2. Kwashiorkor- characterized by edema (swelling of the extremities), and a diminished capacity in the quantity and quality of bodily proteins

1. Emmert, J.L. & Baker, D.H. (1995) Protein quality assessment of soy products. Nutr. Res. 15; 1647-1656.

2. Fuller, M.F. & Garlich, P.J. (1994) Human amino acid requirements: can the controversy be resolved. In: Annual Review of Nutrtion (Olson, R.E., Bier, D.M., & McCormick, D.B., eds.), vol. 14, pp. 217-241. Annual Reviews, Inc. Palo Alto, CA.

3. Hammock, Delia A. “Protein.” Total Nutrition Ed. Victor Herbert, M.D., Genell J. Subak-Sharpe, M.S. New York: Saint Martin’s Griffin, 1995. 94-118.