9 Essential Amino Acids: Benefits & Food Sources

There are more than 500 amino acids found in nature. Amino acids are the smallest unit of protein and indispensable nutrients for the human body.

There are 20 amino acids that the human body requires, both essential and non-essential amino acids. This article explores the health benefits of nine essential amino acids and their food sources.

From the nine essential amino acids to the non-essential amino acids, they can be synthesized by a process called transamination, which takes place in the liver. Synthesis by the body requires vitamin A, and high protein intakes require concomitant vitamin A intake. Vitamin B6 (pyridoxine) is also required for protein synthesis, as are vitamins K and B12.

What are essential amino acids?

Essential amino acids are amino acids that cannot be synthesized by humans in sufficient amounts or at all and therefore must be included in the diet. There are nine essential amino acids (also called indispensable amino acids): histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

Eating a balanced diet can supply us with both the essential and non-essential amino acid building blocks needed to maintain good health. Both nonessential and essential amino acids are present in foods that contain protein. If you don't eat enough essential amino acids, your body first struggles to conserve what essential amino acids it can. However, eventually, your body progressively slows the production of new proteins until, at some point, you break down proteins faster than you can make them. When that happens, health deteriorates.

Adults need only about 11% of their total protein requirement to be supplied by essential amino acids. Typical diets supply an average of 50% of protein as essential amino acids.

The estimated needs for essential amino acids for infants and preschool children are 40% of total protein intake; however, in later childhood, the need drops to 20%.

Essential amino acids play a crucial role in various physiological functions, including protein synthesis, enzyme production, and neurotransmitter regulation. They are essential building blocks for the body, contributing to the structure and function of tissues, organs, and systems.

List of functions and facts about nine essential amino acids

Leucine and Isoleucine

• two of the amino acids known as the branched chain amino acids(BCAA)
• both are commonly deficient in the amino acid profiles of chronically sick individuals
• isoleucine is useful in the formation of haemoglobin

Valine

• needed for normalizing the nitrogen balance in the body
• vital for mental function, muscle coordination, and neural function
• helpful in cases of inflammation
• a branched-chain amino acid

Histidine

• helps to remove toxic metals from the body
• effective in treating ulcers in the digestive tract
• has been successfully used in the treatment of rheumatoid arthritis
• helps maintain the myelin sheaths, which insulate the nerves and are required by the auditory nerve for good function
• stimulates the production of red and white blood cells

Lysine

• often low in vegetarian diets
• important in children's growth and development
• helps in the formation of antibodies to fight disease
• effective in the treatment of the herpes simplex virus, especially when combined with Vitamin C
• enhances concentration

Methionine

• an essential amino acid containing sulfur
• a powerful antioxidant that prevents free radical damage to body tissues
• acts to detoxify heavy metals from the body
• strengthens hair follicles
• assists gallbladder function through the synthesis of bile salts

Phenylalanine

• required by the thyroid for normal function
• needs Vitamin C to be metabolized
• acts as an anti-depressant
• may improve memory, concentration, and mental alertness

Threonine

• prevents the accumulation of fat in the liver
• required for digestive and intestinal tract function
• deficient in grains but abundant in pulses, making a combination of grains and pulses a complete source of protein for vegetarians
• suggested being essential for mental health

Tryptophan

• needed for the synthesis of Vitamin B3 in the body and the precursor of the neurotransmitter serotonin, which is a calming, sedating substance essential for normal mood and sleep patterns
• has powerful painkilling effects
• useful in weight control
• acts as a mood adaptogen—it calms agitation and stimulates depressed individuals

Health benefits and food sources of essential amino acid

1. Isoleucine

Isoleucine is a branched-chain amino acid that plays a key role in regulating blood sugar and energy levels. Plus, it's a vital player in muscle protein synthesis, helping your muscles recover and grow after hitting the gym.

Muscle Repair and Recovery: Isoleucine plays a crucial role in muscle protein synthesis, promoting the repair and recovery of muscle tissues after exertion or injury.

Blood Sugar Balance: Isoleucine assists in regulating blood sugar levels, promoting insulin function, and contributing to glucose metabolism.

Mental Well-being Promoter: Isoleucine is implicated in the synthesis of neurotransmitters, potentially playing a role in mood regulation and cognitive function.

Food Sources: eggs, soy protein, seaweed, turkey, chicken, lamb, cheese, and fish.
Recommended Dietary Allowances: for adults 19 years and older, 19 mg/kg body weight/day.

2. Leucine

Acting as a catalyst for muscle growth, leucine signals the body to unleash its anabolic prowess, fostering the development of lean muscle mass.

Post-exercise, leucine expediting muscle recovery, reducing fatigue, and fortifying the resilience of the muscular framework.

Leucine plays a role in regulating blood sugar levels and enhancing insulin sensitivity, contributing to overall metabolic health.

Food sources: whey protein, soy products, beef, peanuts, salmon, almonds, chicken, and eggs.
Recommended Dietary Allowances: for adults 19 years and older, 42 mg/kg body weight/day.

3. Valine

Valine helps supply energy to your muscles, particularly during endurance activities or when the body is in need. Valine can be converted into glucose, serving as an energy source for your muscles. This is particularly handy during intense workouts or times when your body needs an extra energy kick.

Muscle Repair: Like its BCAA buddies, valine is involved in muscle protein synthesis. This means it helps repair and rebuild muscle tissue, keeping your muscles in tip-top shape.

Nitrogen Balance: Valine plays a role in maintaining nitrogen balance in the body, which is crucial for various physiological functions, including the synthesis of other important molecules.

Food sources: meats, dairy products, soy products, beans and legumes.
Recommended Dietary Allowances: for adults 19 years and older, 24 mg/kg body weight/day.

4. Histidine

Histidine serves as an essential amino acid for the growth of children, while for adults, it falls under the category of non-essential amino acids.
During the rapid growth phase of childhood, the body's demand is substantial, surpassing its endogenous production capacity, necessitating intake from dietary sources.

Precursor to Histamine: Histidine is a precursor to histamine, a neurotransmitter involved in various physiological processes, including immune response and regulation of stomach acid.

Metal Binding: Histidine is a metal-binding amino acid, playing a role in the structure and function of metalloproteins. These proteins are involved in processes like oxygen transport and DNA repair.

pH Regulation: Histidine can act as a buffer, helping to regulate the pH balance in your body.

Muscle Tissue Repair: Histidine is involved in the formation of carnosine, a dipeptide that's abundant in muscle tissues. Carnosine plays a role in buffering lactic acid during exercise and may contribute to muscle endurance.

Neurotransmitter Regulation: Apart from histamine, histidine is involved in the synthesis of other neurotransmitters, contributing to proper nervous system function.

Food Sources: Meat, poultry, fish, dairy products, and whole grains.
Recommended Dietary Allowances: for adults 19 years and older, 14 mg/kg body weight/day.

5. Lysine

Lysine plays several roles in humans, most importantly proteinogenesis, but also in the crosslinking of collagen polypeptides, uptake of essential mineral nutrients, and in the production of carnitine, which is key in fatty acid metabolism.

Due to its importance in several biological processes, a lack of lysine can lead to several disease states including defective connective tissues, impaired fatty acid metabolism, anaemia, and systemic protein-energy deficiency. In contrast, an overabundance of lysine, caused by ineffective catabolism, can cause severe neurological disorders.

Collagen Formation: Lysine plays a crucial role in the formation of collagen, the protein that provides structure to your skin, bones, and connective tissues. It's like the architect ensuring everything stays firm and resilient.

Calcium Absorption: Lysine helps your body absorb calcium, supporting bone health.

Virus Inhibition: Lysine has been associated with inhibiting the replication of certain viruses, particularly those that cause cold sores.

Carnitine Production: Lysine is involved in the production of carnitine, a molecule essential for converting fatty acids into energy. It's like the energy manager, ensuring a smooth fuel conversion process.

Food sources: eggs, meat, soybeans and peas, cheese, cod, and sardines.
Recommended Dietary Allowances: for adults 19 years and older, 38 mg/kg body weight/day.

6. Methionine

Methionine as the precursor of other non-essential amino acids such as cysteine and taurine, versatile compounds such as SAM-e, and the important antioxidant glutathione, methionine plays a critical role in the metabolism and health of many species, including humans. Methionine is also involved in angiogenesis and various processes related to DNA transcription, epigenetic expression, and gene regulation.

Antioxidant Properties: Methionine provides sulfur for the synthesis of other sulfur-containing molecules like glutathione, a powerful antioxidant.

Detoxification Support: Methionine is involved in the methylation process, a key player in detoxification pathways.

Collagen Formation: Methionine contributes to collagen formation, supporting the health of your skin, hair, and nails.

Fat Metabolism: Methionine is essential for the metabolism of fats, helping prevent the buildup of excess fat in the liver.

Food sources: eggs, cheese, meat, fish, sesame seeds, and Brazil nuts.
Recommended Dietary Allowances: for adults 19 years and older, 19 mg/kg body weight/day.

7. Phenylalanine

Phenylalanine is a precursor for tyrosine, the monoamine neurotransmitters dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline), and the skin pigment melanin.

Phenylalanine is found naturally in the milk of mammals. It is used in the manufacture of food and drink products and sold as a nutritional supplement for its analgesic and antidepressant effects. It is a direct precursor to the neuromodulator phenethylamine, a commonly used dietary supplement.

Precursor to Neurotransmitters: Phenylalanine is a precursor to key neurotransmitters like dopamine, norepinephrine, and epinephrine.

Mood Regulation: Thanks to its role in neurotransmitter production, phenylalanine is linked to mood regulation.

Pain Relief: Phenylalanine has been associated with pain relief, particularly in conditions like chronic pain and migraines.

Skin Pigment Production: Phenylalanine is involved in the production of melanin, the pigment responsible for skin, hair, and eye color. It's like the artist adding the hues to your natural canvas.

Food sources: eggs, chicken, liver, beef, milk, and soybeans.
Recommended Dietary Allowances: for adults 19 years and older, 25 mg/kg body weight/day.

8. Threonine

Collagen and Elastin Production: Threonine is involved in the formation of collagen and elastin, essential proteins for skin elasticity and connective tissue health.

Immune System Support: Threonine plays a role in the production of antibodies and immune system proteins, contributing to your body's defense against infections.

Central Nervous System Function: Threonine is a precursor to glycine and serine, both of which play important roles in the central nervous system.

Fat Metabolism: Threonine is involved in the metabolism of fats, helping your body process dietary fats efficiently.

Foods sources: cheese, poultry, fish, meat, lentils, black turtle bean and sesame seeds.
Recommended Dietary Allowances: for adults 19 years and older, 20 mg/kg body weight/day.

9. Tryptophan

Serotonin Production: Tryptophan is a precursor to serotonin, a neurotransmitter that regulates mood, appetite, and sleep. Insufficient tryptophan may precipitate mental tension, giving rise to symptoms such as insomnia.

Melatonin Synthesis: Tryptophan is also a precursor to melatonin, the hormone that regulates sleep.

Niacin (Vitamin B3) Conversion: Tryptophan can be converted into niacin, an essential B vitamin important for energy metabolism, skin health, and nerve function.

Reducing Anxiety and Stress: Through its role in serotonin production, tryptophan may help reduce symptoms of anxiety and stress.

Regulating cholesterol levels and ameliorating symptoms of menopause.

See the full benefits of tryptophan for more information.

Food sources: chocolate, oats, dried dates, milk, yogurt, cottage cheese, red meat, eggs, fish, poultry, sesame, chickpeas, almonds, sunflower seeds, pumpkin seeds, hemp seeds, buckwheat, spirulina, and peanuts.
Recommended Dietary Allowances: for adults 19 years and older, 5 mg/kg body weight/day.