Amino acids are building blocks of protein, which is required in your body to make enzymes, muscle tissue, skin, hair and fingernails, among other things. Of the 22 amino acids used by humans, eight are considered essential for adults, meaning that the human body cannot synthesize them. Children have different requirements for amino acids, not only because of their smaller size and faster growth rates, but because they are unable to make additional amino acids while young.
Function of Amino Acids
Amino acids are usually consumed as protein, either from animals or plant sources, then broken down into amino acids within your gastrointestinal system. Some amino acids are used immediately, while others are combined to make additional amino acids. Amino acids are used individually for a variety of biochemical reactions in your body and are also combined to form protein-based substances and structures, such as muscle fiber and connective tissues. A deficiency of amino acids, usually caused by inadequate dietary protein, leads to stunted growth, lack of energy, muscle weakness, poor immune response and unhealthy looking hair and skin, as described in "Human Biochemistry and Disease."
Essential Amino Acids
The eight amino acids considered essential for healthy adults are isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. According to "Biochemistry of Human Nutrition," four additional amino acids are essential for infants and small children because of their underdeveloped digestive system and they include cysteine, tyrosine, histidine and arginine. Cysteine, tyrosine and histidine become nonessential amino acids for children as they grow older depending on physical maturity, so a child by the age of 10 or so may need only nine amino acids from dietary sources. As most children become teenagers, their amino acid requirements become the same as adults.
Arginine
Although considered an essential amino acid for infants and young children, arginine is actually made by your body during all stages, but at a much slower rate in the early years. Arginine plays an important role in cellular division, wound healing, protein synthesis, immunity, hormonal secretion and ammonia removal, according to "Biochemical, Physiological and Molecular Aspects of Human Nutrition." Like all amino acids, arginine is found in a wide variety of foods such as dairy products, beef, chicken, pork, seafood, fish, wheat, most nuts, many seeds, some legumes and cooked soybeans.
Phenylketonuria
Phenylketonuria, or PKU, is a genetic disease that disables the use of the amino acid phenylalanine. Children with PKU must dramatically reduce their dietary intake of phenylalanine to prevent mental retardation and other metabolic complications resulting from buildup, according to "Advanced Nutrition and Human Metabolism." However, they cannot synthesize tyrosine from phenylalanine, so tyrosine becomes an essential amino acid in children and adults with PKU.
References
- "Human Biochemistry and Disease"; Gerald Litwack; 2008
- "Biochemistry of Human Nutrition"; George Gropper; 2000
- "Biochemical, Physiological and Molecular Aspects of Human Nutrition"; Martha Stipanuk; 2006
- "Advanced Nutrition and Human Metabolism: 5th Edition"; Sareen S. Gropper and Jack L. Smith; 2009
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