Amino Acids Explained: Types, Benefits & Food Sources

Amino Acids: The Building Blocks of Life

What Are Amino Acids? 

Amino acids are the building blocks that the body uses for protein synthesis (protein production). In other words, proteins are made up of long chains of amino acids. There are 20 standard amino acids (basic amino acids) in the human body — 9 essential amino acids from food and 11 nonessential amino acids produced by the body. 

Amino acid metabolism is the process by which the body breaks down and uses these molecules to produce proteins, hormones, enzymes, and other chemicals required for proper bodily functions.

Each protein is made up of a sequence of many amino acids, which give it a unique structure and function in the body. There are thousands of proteins in the body, each with a unique amino acid composition. You can think of amino acids as letters of the alphabet and proteins as different words. 

Structure of Amino Acids

Amino acids are organic chemicals made up of carbon-hydrogen bonds. The basic structure of all amino acids is similar, consisting of a central carbon atom attached to an acidic carboxyl group, a hydrogen atom, and an R group (a side chain). The amino acid glycine is the simplest amino acid. 

Each amino acid has a unique R group, which determines its chemical nature and overall function. The unique characteristic of each R group influences the chemical reactions between a specific amino acid and other molecules in the body. Two amino acids can link together through peptide bond formation. Peptide bonds between amino acids lead to the creation of three-dimensional functional groups called proteins.

There are various types of amino acid molecules, such as alpha amino acids (α-amino acids), where the amino groups and carboxylic acid group are attached to the α-carbon; β-amino acids, where the amino group is attached to the β-carbon; and gamma amino acids (γ-amino acids) which are amino acid residues containing three carbon atoms as a backbone between the amino and carbonyl groups.

The Role of Amino Acids in the Body

The specific functions of the nine essential amino acids in the body are broadly listed below:

• Histidine: Formation of the brain chemical (neurotransmitter) histamine, immune system function, sleep, digestion, and sexual function.

• Leucine: Biosynthesis of protein and growth hormones, muscle tissue repair, wound healing, and blood sugar regulation.

• Isoleucine: Immune function, muscle metabolism, hemoglobin formation, energy regulation. 

• Lysine: Hormone production, calcium metabolism, immune system functioning. 

• Methionine: Tissue regeneration and growth, detoxification, metabolism, nutrient absorption.

• Phenylalanine: Formation of dopamine, epinephrine, norepinephrine (neurotransmitters), and synthesis of other amino acids.

• Threonine: Elastin and collagen synthesis, formation of blood clots, fat metabolism, and immunity.

• Tryptophan: Nitrogen balance, serotonin formation. 

• Valine: Tissue regeneration, muscle growth, energy production. 

What Are the 5 Main Amino Acids?

Essential Amino Acids

Amino acids that the body cannot make are called essential amino acids. These amino acids must be obtained from dietary sources. The nine essential amino acids (indispensable amino acids) are:

• Histidine

• Leucine

• Isoleucine

• Lysine

• Methionine

• Threonine

• Phenylalanine

• Tryptophan

• Valine

Non-Essential Amino Acids

Nonessential amino acids are the 11 amino acids that the body can produce. They are:

• Arginine

• Alanine

• Aspartic acid

• Asparagine

• Cysteine

• Glycine 

• Glutamine

• Glutamic acid

• Serine

• Proline

• Tyrosine

Others: What Are Conditional Amino Acids?

Conditional amino acids are semi-essential amino acids that are partially synthesized in the body but not in sufficient amounts. They are also called conditionally essential amino acids (CEAA). Semi-essential amino acids are needed for growth and are essential for growing children, pregnant women, and lactating women. They may also be needed in increased amounts during illnesses and injuries. Three amino acids are considered semi-essential or conditional amino acids—arginine, histidine, and glycine.

What Are Branched Chain Amino Acids?

Branched-chain amino acids (BCAAs are three essential amino acids—leucine, isoleucine, and valine—that the body uses for muscle energy. BCAAs can be found in dairy, meat, and legumes; they are also available as supplements.

The Requirement for Amino Acids

As noted, the body needs to obtain essential amino acids from food sources. The recommended dietary allowances for the essential amino acids are listed below in milligrams (mg) per 2.2 pounds (lbs) or about 1 kilogram (kg) of body weight per day:

• Leucine: 42 mg

• Lysine: 38 mg

• Phenylalanine: 33 mg

• Valine: 24 mg

• Threonine: 20 mg

• Isoleucine: 19 mg

• Methionine: 19 mg

• Histidine: 14 mg

• Tryptophan: 5 mg

Recommended Dietary Protein Intake

The recommended dietary allowances (RDA) for protein in different age groups, in grams of protein per kilogram of body weight per day, are as follows: 

• Children 1–3 years old: 1.2 g/kg/day 

• Children 4–6 years old: 1.1 g/kg/day

• Children 7–14 years old: 1.0 g/kg/day

• Teenagers 15–18 years old: 0.8 to 1.2 g/kg/day

• Adults with minimal physical activity: 0.8 g/kg/day

• Adults with moderate physical activity: 1.3 g/kg/day

• Adults with intense physical activity: 1.6 g/kg/day

In addition to the above RDAs for protein, you can use the below recommendation for minimum protein intake in grams (g) per day for different age groups:

• Babies 6-11 months: 11 g/day

• Children 1-3 years old: 13 g/day

• Children 4-8 years old: 19 g/day

• Males:

  • 9-13 years old: 34 g/day

  • 14-18 years old: 52 g/day

  • 19-70 years and older: 56 g/day

• Females:

  • 9-13 years old: 34 g/day

  • 14-70 years old: 46 g/day

• Pregnant and breastfeeding individuals (at any age): 71 g/day 

Sources of Amino Acids

Foods Rich in Amino Acids: What Foods Have All 20 Amino Acids?

Animal proteins are some of the best sources of amino acids. Foods that contain all the amino acids (nine essential amino acids) are called complete proteins. Examples of complete proteins include poultry, fish, beef, eggs, dairy products, quinoa, buckwheat, and soy products (edamame, tofu). Amino acids obtained from animal proteins are easy for the body to absorb and use. 

Foods that contain certain amino acids but not all nine of the essential amino acids are called incomplete proteins. Examples of incomplete proteins include plant proteins such as beans, certain whole grains, nuts, and seeds. 

How to Eat Foods with Essential Amino Acids

You don’t have to eat every amino acid every day, but it’s important to eat a varied, balanced, healthy diet to get all nine essential amino acids from dietary sources. If you are a vegetarian or vegan, it is especially important to include a variety of plant-based proteins in your diet to ensure you get all nine essential amino acids.

Amino Acid Supplements: Is It Safe To Take Amino Acids Every Day?

Most healthy people do not need to take essential amino acid supplements. Eating a healthy, balanced diet can ensure you get all the common amino acids found in food sources. 

Some dietary supplements containing amino acids claim to improve sleep or enhance athletic performance. However, these claims are not supported by robust scientific evidence. Keep in mind that the U.S. Food and Drug Administration (FDA) does not regulate dietary supplements, including amino acid supplements. 

Talk with your healthcare provider before taking any amino acid supplements if you feel you are not getting enough essential amino acids from your diet.

Can You Be Deficient in a Specific Amino Acid?

A deficiency of individual amino acids is rare. However, people who eat certain diets may develop a deficiency of certain amino acids. For example, corn-based diets can lead to tryptophan and lysine deficiency. Peanut and soy-based diets can lead to methionine deficiency. 

As mentioned, most people get enough amino acids from dietary sources, provided they eat a healthy, balanced diet. However, people who only eat plant foods may not get all the essential amino acids because several amino acids are mainly found in animal foods (complete proteins). 

Benefits: What Does Taking Amino Acids Do To Your Body?

Hormone Regulation

Tryptophan is an essential amino acid that the body uses to make a neurotransmitter called serotonin. Serotonin plays a key role in regulating mood, appetite, and sleep. Taking amino acid supplements containing tryptophan may help people with mood and sleep disturbances by raising the levels of serotonin in the body. Some studies have found that taking tryptophan at doses of up to 3 grams per day can improve mood.

Muscle Building and Recovery

Three essential branched-chain amino acids—leucine, isoleucine, and valine—may enhance athletic performance and help muscle recovery following exercise. Small studies have shown that taking leucine, isoleucine, and valine in a 2:1:1 ratio at a dose of 0.039 grams per pound of body weight improves exercise performance and leads to less muscle soreness and faster recovery. 

Studies have also shown that branched-chain amino acids reduce muscle soreness and promote recovery after intense exercise more so than rest. In addition, taking branched-chain amino acids has been found to reduce perceived exertion (how hard you think you’re exercising).

Wound Healing

Studies have shown that people who received conditionally essential amino acids after surgery for bone fractures had fewer medical complications during recovery and a lower mortality rate. Researchers have also found that cancer patients who receive branched-chain amino acids are less likely to develop complications such as infections and fluid collection in the abdomen. Additionally, controlled clinical trials suggest that older adults recovering from knee replacement surgery have reduced loss of muscle mass if they receive essential amino acid supplements.

Weight Loss

Further research is needed, but some studies suggest that fine-tuning the quality and quantity of proteins or even specific amino acids may be beneficial in managing body composition, metabolic syndrome, and appetite regulation in obese and overweight individuals. Restrictions of specific amino acids, such as branched-chain amino acids (BCAA), methionine, tryptophan, and glutamate, could play a role in chronic weight management.