Amino acids are the building blocks of proteins and play an important role in body functions. They are needed for vital processes like the cell building and synthesis of hormones and neurotransmitters (brain chemicals). They may also be taken as supplements. There 20 different amino acids required for the body to function properly, of which nine are considered essential. The essential amino acids are not synthesized in the body and must be obtained externally, through diet or supplements. The nonessential amino acids are synthesized by the body.
The nine essential amino acids are tryptophan, histidine, isoleucine, leucine, methionine, lysine, phenylalanine, threonine, and valine. When protein is consumed, it’s broken down into amino acids in the gut, which is used for various body processes, such as fueling the body, building muscle, tissue repair, boosting the immune system, synthesis of hormones, functioning of neurotransmitter and enzymes, and other biological processes. The best sources of essential amino acids are animal proteins like meat, eggs, and poultry. Soya and tofu are good vegan protein options. The nonessential amino acids are synthesized by the body. Though they are called nonessential, they are still involved in several body functions. Some non-essential amino acids are categorized as conditionally essential. They are considered essential only in specific circumstances, such as stress or illnesses. For example, arginine is nonessential but considered essential when the body is fighting certain diseases like cancer. Hence, arginine would have to be supplemented through diet or supplements during an illness.
The roles of essential amino acids in the body
The nine essential amino acids perform several important and varied jobs in your body:
- Phenylalanine: Phenylalanine is a precursor for brain chemicals like dopamine, epinephrine, and norepinephrine. These chemicals are brain messengers. It also helps in forming the structure and functioning of proteins, enzymes, and synthesis of other amino acids.
- Valine: Valine helps in muscle growth, tissue regeneration, and is required for energy production.
- Threonine: Threonine is an important part of structural proteins, such as collagen and elastin, which provide structure to the skin and connective tissue and help in the formation of blood clots, thus preventing bleeding. Threonine also helps in fat metabolism and boosting immune function.
- Tryptophan: Tryptophan helps maintain proper nitrogen balance. It helps in the synthesis of serotonin, a neurotransmitter. Serotonin regulates mood, appetite, and sleep.
- Methionine: Methionine helps in tissue growth, metabolism, and detoxification of the body, as well as absorption of essential minerals, such as zinc and selenium.
- Leucine: Leucine helps in protein synthesis, muscle repair, muscle growth, wound healing, regulation of blood sugar levels, and synthesis of growth hormones.
- Isoleucine: Isoleucine helps in muscle metabolism, boosting immune function, synthesis of hemoglobin, and regulation of energy.
- Lysine: Lysine helps in the synthesis of protein, enzymes, hormones (collagen and elastin), calcium absorption, energy production, and immune function.
- Histidine: Histidine is involved in the synthesis of histamine, which is a neurotransmitter that helps immune function, digestion, sleep regulation, and sexual function. It also helps maintain the myelin sheath (protective barrier surrounding nerve cells).
Sources and recommended dietary intake of amino acids
Since the body cannot synthesize essential amino acids, they must be supplemented through diet or supplements.
The following foods contain all the nine essential amino acids, hence also called complete proteins:
- Dairy products
The recommended daily allowances of essential amino acids per kg body weight are:
- Histidine: 14 mg
- Tryptophan: 5 mg
- Valine: 24 mg
- Isoleucine: 19 mg
- Leucine: 42 mg
- Lysine: 38 mg
- Threonine: 20 mg
- Methionine (and the nonessential amino acid cysteine): 19 mg
- Phenylalanine (and the nonessential amino acid tyrosine): 33 mg
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Science Direct. Amino Acid. https://www.sciencedirect.com/topics/medicine-and-dentistry/amino-acid
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