Amino Acid Basics Protein always seems to receive its fair share of attention in the news. Amino acid buzzwords often are used, but taken out of context, this information often is misleading. This article provides a frame of reference as to what the news actually means about amino acids and protein. Role of protein Carbohydrate, fat, alcohol, and protein are all composed of three elements—carbon, hydrogen, and oxygen. However, protein also has an additional element of nitrogen, and that is what makes it unique. The nitrogen is responsible for the role of protein—to build and repair body tissues, produce hormones and digestive enzymes, and provide immune functioning. Protein is not efficiently used for energy production, but in certain circumstances it is used for energy. Protein is made up of amino acids. Twenty-two amino acids are known to have a role in building and repairing body tissues and forming enzymes. Amino acids are found in foods in different concentrations and combinations. It is possible for the human body to synthesize (break down and reconfigure) most amino acids; these are called nonessential or dispensable amino acids. It is not possible to synthesize some amino acids, so these essential or indispensable amino acids must come from foods. Amino acids often are referred to as “building blocks,” because they build tissue. Essential amino acids (indispensable amino acids) The following are essential amino acids: Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine Nonessential amino acids (dispensable amino acids) The following are nonessential amino acids: Alanine Arginine Asparagine Aspartic acid Cysteine Cystine Glutamic acid Glutamine Glycine Hydroxyproline Proline Serine Tyrosine Conditionally essential (indispensable) amino acids Certain amino acids are needed under certain conditions when synthesis becomes limited or the body cannot meet its needs, such as when the body is under stress. These are referred to as conditionally essential amino acids. Sources vary as to which amino acids are considered conditionally essential. Both cysteine and tyrosine fall on all lists of conditionally essential amino acids from various sources, but some lists also include arginine, glutamine, glycine, ornithine, proline, and serine. Not enough protein In the average American diet, it is extremely rare to have a protein deficiency. Vegetarian and vegan diets require some extra attention to protein, but nuts, beans, many starches, soy, and dairy products and eggs (for individuals who eat dairy products and eggs) can more than adequately provide for protein needs. Kwashiorkor refers to a condition resulting from not having enough protein, but in the presence of adequate caloric intake. If the diet does not have enough protein and calories, the condition is termed marasmus or protein-energy malnutrition. This condition is common in third-world countries, in hospital settings, and with conditions of extreme physiological stress. Too much protein Excess protein in the diet sometimes is taxing to the kidneys and limits calcium absorption. Because protein often is present in high-fat foods, excess protein may lead to excess fat intake, which may promote obesity, cardiovascular disease, and cancer. Protein recommendations For the average adult, 0.8 gram (g) of protein/kilogram (kg) body weight is recommended. Average requirement is between 45 to 60 g/day. Protein needs are higher and are individualized for: Children Convalescent patients Individuals with medical conditions such as: – Burns – Hemorrhage – Protein malnutrition – Surgery – Wounds Infants Pregnant women Bodybuilding Taking large doses of amino acids will not make muscles bigger or stronger. To date, no scientific evidence exists to prove that individual amino acids have a bodybuilding effect. The same is true for protein supplementation. Athletes need more protein than sedentary adults: Power athletes (strength or speed): 1.2 to 1.7 g/kg/day Endurance athletes: 1.2 to 1.4 g/kg/day Most athletes can get the recommended amount of protein through diet alone, without the use of supplements. Protein powders and protein supplements are great for convenience, but are not necessary, even for elite athletic performance. References and recommended readings Caspero A. Protein and the athlete—how much do you need? EatRight.org Web site. http://www.eatright.org/Public/content.aspx?id=6442477918. Accessed May 29, 2014. Mathews DE. Proteins and amino acids. In: Ross AC, Cabellero B, Cousins RJ, Tucker KL, Ziegler TR, eds. Modern Nutrition in Health and Disease. 11th ed. Baltimore, MD: Lippincott Williams and Wilkins; 2014:3-35. MedlinePlus. Amino acids. US National Library of Medicine, National Institutes of Health Web site. http://www.nlm.nih.gov/medlineplus/ency/article/002222.htm. Updated February 18, 2013. Accessed May 29, 2014. Review Date 5/14 G-1001