The body needs 20 different amino acids to maintain good health and normal functioning. People must obtain nine of these amino acids, called the essential amino acids, through food. Good dietary sources include meat, eggs, tofu, soy, buckwheat, quinoa, and dairy.

Amino acids are compounds that combine to make proteins. When a person eats a food that contains protein, their digestive system breaks the protein down into amino acids. The body then combines the amino acids in various ways to carry out bodily functions.

A healthy body can manufacture the other 11 amino acids, so these do not usually need to enter the body through the diet.

Amino acids build muscles, cause chemical reactions in the body, transport nutrients, prevent illness, and carry out other functions. Amino acid deficiency can result in decreased immunity, digestive problems, depression, fertility issues, lower mental alertness, slowed growth in children, and many other health issues.

Each of the essential amino acids plays a different role in the body, and the symptoms of deficiency vary accordingly.

Types of essential amino acids
High protein foods, such as tofu and quinoa, contain amino acids.
There are many types of essential amino acids, including:

Lysine
Lysine plays a vital role in building muscle, maintaining bone strength, aiding recovery from injury or surgery, and regulating hormones, antibodies, and enzymes. It may also have antiviral effects.

There is not a lot of research available on lysine deficiency, but a study on ratsTrusted Source indicates that lysine deficiency can lead to stress-induced anxiety.

Histidine
Histidine facilitates growth, the creation of blood cells, and tissue repair. It also helps maintain the special protective covering over nerve cells, which is called the myelin sheath.

The body metabolizes histidine into histamine, which is crucial for immunity, reproductive health, and digestion. The results of a study that recruited women with obesity and metabolic syndrome suggest that histidine supplements may lower BMI and insulin resistance.

Deficiency can cause anemia, and low blood levels appear to be more common among people with arthritis and kidney disease.

Threonine
Threonine is necessary for healthy skin and teeth, as it is a component in tooth enamel, collagen, and elastin. It helps aid fat metabolism and may be beneficial for people with indigestion, anxiety, and mild depression.

A 2018 study found that threonine deficiency in fish led to these animals having a lowered resistance to disease.

Methionine
Methionine and the nonessential amino acid cysteine play a role in the health and flexibility of skin and hair. Methionine also helps keep nails strong. It aids the proper absorption of selenium and zinc and the removal of heavy metals, such as lead and mercury.

Valine
Valine is essential for mental focus, muscle coordination, and emotional calm. People may use valine supplements for muscle growth, tissue repair, and energy.

Deficiency may cause insomnia and reduced mental function.

Isoleucine
Isoleucine helps with wound healing, immunity, blood sugar regulation, and hormone production. It is primarily present in muscle tissue and regulates energy levels.

Older adults may be more prone to isoleucine deficiency than younger people. This deficiency may cause muscle wasting and shaking.

Leucine
Leucine helps regulate blood sugar levels and aids the growth and repair of muscle and bone. It is also necessary for wound healing and the production of growth hormone.

Leucine deficiency can lead to skin rashes, hair loss, and fatigue.

Phenylalanine
Some diet sodas contain sweeteners with phenylalanine.
Phenylalanine helps the body use other amino acids as well as proteins and enzymes. The body converts phenylalanine to tyrosine, which is necessary for specific brain functions.

Phenylalanine deficiency, though rare, can lead to poor weight gain in infants. It may also cause eczema, fatigue, and memory problems in adults.

Phenylalanine is often in the artificial sweetener aspartame, which manufacturers use to make diet sodas. Large doses of aspartame can increase the levels of phenylalanine in the brain and may cause anxiety and jitteriness and affect sleep.

People with a rare genetic disorder called phenylketonuria (PKU) are unable to metabolize phenylalanine. As a result, they should avoid consuming foods that contain high levels of this amino acid.

Tryptophan
Tryptophan is necessary for proper growth in infants and is a precursor of serotonin and melatonin. Serotonin is a neurotransmitter that regulates appetite, sleep, mood, and pain. Melatonin also regulates sleep.

Tryptophan is a sedative, and it is an ingredient in some sleep aids. One study indicates that tryptophan supplementation can improve mental energy and emotional processing in healthy women.

Tryptophan deficiency can cause a condition called pellagra, which can lead to dementia, skin rashes, and digestive issues.

Essential amino acids and exercise
Many studies show that low levels of protein and essential amino acids affect muscle strength and exercise performance.

According to a 2014 study, not getting enough essential amino acids may cause lower muscle mass in older adults.

An additional study shows that amino acid supplements can help athletes recover after exercise.