Proteins play a role in almost every structure and function in your body. Proteins are the basis for forming enzymes, hormones, neurotransmitters, skin, muscle, bones and blood cells. Twenty percent of the human body is composed of protein. Your dietary habits, including your protein intake, can influence the way your body functions. Certain amino acids, the components that form a protein, cannot be synthesized by the body and must be consumed through diet.
Essential Amino Acids
Your body links certain combinations of amino acids together to form different proteins. There are 20 amino acids that your body uses to make all the proteins it needs. Your body can synthesize 10 of these amino acids, but the other 10 must be obtained through the diet. The 10 amino acids your body cannot produce are termed essential amino acids, because they are an essential part of the diet. Your body is unable to produce arginine, histidine, isoleucine, tryptophan, valine, phenylalanine, threonine, lysine and methionine.
Choosing a Protein
Not all sources of protein are equal. Some dietary proteins are better sources of the essential amino acids than others. Your body can digest and absorb some proteins better than others as well. A system of rating protein is known as the protein digestibility corrected amino acid score, or PDCAAS. This score indicates the usefulness and quality of a protein, taking into consideration protein lost during digestion. Foods are given a score of zero to 100, or more if the protein is of high quality. High quality sources of protein include eggs, milk, beef and soy. Eggs rate at a 118; milk is given 121; beef scores a 92; and soy is rated 91.
Significance
Protein deficiency is rare in developed countries, but when it does occur it can lead to serious health problems, including a reduction in IQ and even mental retardation. Symptoms of a protein deficiency include growth problems, muscle atrophy, vulnerable immune system, swelling of the abdomen and legs, fatty liver, apathy, diarrhea and anemia.
Intake Recommendations
Your required protein intake varies depending on age, gender, activity level, body composition, health and weight. For specific protein requirements, consult your doctor or a nutritionist. In general, adult men should consume approximately 56 g of protein per day, while adult women need about 46 g per day. During pregnancy or breastfeeding, women should take in 71 g of protein each day.
References
- Medical News Today: What Are Proteins?; Christian Nordqvist; July 2010
- University of Arizona: Amino Acids; September 2003
- "American Journal of Clinical Nutrition"; Protein Quality Assessment: Impact of Expanding Understanding of Protein and Amino Acid Needs for Optimal Health; D. Joe Millward, et al.; 2008
- "Prinicipals of Nutritional Assessment"; Rosalind S. Gibson; 2005
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