Your body uses amino acids to build the proteins that make up your tissues and organs and regulate the vast majority of physiological functions. Many of these amino acids the body produces on its own, but there are 9 essential amino acids that the body cannot make. Your body depends on YOU to feed it these critical nutrients via diet and supplementation.
How Many Essential Amino Acids Are There?
The 9 essential amino acids are:
Don’t be confused if you’ve heard there were just 8 essential amino acids. Experts used to think infants were the only humans that couldn’t make histidine in the body. Modern research shows that adults also rely upon dietary sources of this amino acid, making it 9th on the list. Some sources cite 10 essential amino acids, listing arginine as the final player. I like to classify arginine as a conditionally essential amino acid, which means it’s necessary to get this amino acid from your diet under certain conditions, such as times of illness. Premature infants likewise need arginine because they cannot yet make their own. Let’s briefly summarize what each of the 9 essential amino acids do in your body.
What Do Essential Amino Acids Do?
- Histidine: Children require dietary sources of histidine, while adults can produce some histidine but not enough to meet requirements. Histidine is involved in the synthesis of hemoglobin, tissue repair, and the strengthening of the immune system. In the central nervous system, it helps maintain myelin sheaths that protect nerve cells. Histidine is also metabolized to the neurotransmitter histamine, which influences immunity, gastric function, and sexual function. You don’t want to take an anti-histamine before a romantic interlude!
- Isoleucine: The second of three branched-chain amino acids, isoleucine is a vital component of hemoglobin, the protein in red blood cells that transports oxygen. We need isoleucine for proper blood clotting, muscle repair, and blood sugar regulation, so we can recover faster from strenuous exercise.
- Leucine: One of three branched-chain amino acids, leucine is the most abundant essential amino acid in muscle. It promotes muscle recovery after vigorous workouts and enhances stamina and endurance. Leucine also acts as a signal to activate various cellular functions, including initiating the process of protein synthesis.
- Lysine: Like all the other essential amino acids, lysine is needed to make new body proteins, but it is also a critical agent in the intestinal absorption of calcium. Lysine is a standout nutrient for the immune system because it helps produce antibodies and has important antiviral properties. As a nutritional supplement, lysine seems to be active against herpes simplex viruses (HSV). While lysine is abundant in many animal proteins (red meats, fish, and dairy products), it is typically the limiting amino acid in plant proteins. Vegetarians and especially vegans must be diligent in choosing proteins or opt for supplements to ensure adequate lysine intake.
- Methionine: This sulfur-containing amino acid is a safe dietary approach to ensure adequate sulfur intake. Methionine occupies a unique position among the essential amino acids, because without it, the synthesis of protein never gets started. Methionine also promotes the formation of collagen and cartilage tissue, and has anti-inflammatory, antioxidant, and analgesic properties. Methionine is essential for the absorption and bio-availability of selenium and zinc, aids in detoxification and excretion of chemicals such as lead and mercury, and helps the liver metabolize fats.
- Phenylalanine: Important in the structure and function of many proteins and enzymes, phenylalanine is also a precursor of another amino acid, tyrosine. Tyrosine is converted into a number of brain chemicals that affect mood, focus, and other facets of cognitive function, so different forms of phenylalanine have been proposed to treat mood disorders, stress, anxiety, and pain.
- Threonine: This blood-sugar-regulating amino acid helps keep connective tissues and muscles throughout the body strong and elastic. Threonine also builds robust bones and tooth enamel, and may speed wound healing or recovery from injury. Threonine plays an important role in fat metabolism and prevents fat accumulation in the liver.
- Tryptophan: Tryptophan is necessary for normal growth in infants and for maintaining a balance between protein synthesis and breakdown in adults. Tryptophan is widely recognized as a precursor of the neurotransmitter serotonin; hence, its use as an antidepressant and sleep aid.
- Valine: The third branched-chain amino acid, valine assists in tissue repair, muscle metabolism, and blood sugar control. It also helps regulate nitrogen balance and determine the three-dimensional structure of proteins.