Proteins are the building blocks for everything that helps us grow. Think of carbs and fats as energy and proteins as the framework. Proteins are made up of 20 amino acids, nine of which are essential, which we need to get from our food. The others are nonessential, meaning that the proteins we do eat can be transformed, like Lego that can be restructured to make another protein.
The 9 essential amino acids are: lysine, histidine, threonine, methionine, valine, isoleucine, leucine, phenylalanine, and tryptophan.
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.
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 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 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 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 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 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 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.
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. Tryptophan deficiency can cause a condition called pellagra, which can lead to dementia, skin rashes, and digestive issues.
The foods in the following list are the most common sources of essential amino acids:
- Lysine is in meat, eggs, soy, black beans, quinoa, and pumpkin seeds.
- Meat, fish, poultry, nuts, seeds, and whole grains contain large amounts of histidine.
- Cottage cheese and wheat germ contain high quantities of threonine.
- Methionine is in eggs, grains, nuts, and seeds.
- Valine is in soy, cheese, peanuts, mushrooms, whole grains, and vegetables.
- Isoleucine is plentiful in meat, fish, poultry, eggs, cheese, lentils, nuts, and seeds.
- Dairy, soy, beans, and legumes are sources of leucine.
- Phenylalanine is in dairy, meat, poultry, soy, fish, beans, and nuts.
- Tryptophan is in most high-protein foods, including wheat germ, cottage cheese, chicken, and turkey.