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