Amino acids are small compounds used to build proteins. The body uses them when producing structural proteins, enzymes, hormones, neurotransmitters and other substances needed for normal biological processes. Some amino acids must be obtained through food, while others can be produced by the body. Different foods and protein supplements provide different combinations and proportions.
This guide explains what amino acids do, the difference between essential and non-essential amino acids, how they form peptides and proteins, and where they can be found in the diet.
What Are Amino Acids?
Amino acids are organic compounds containing several basic chemical components, including an amino group and a carboxyl group. Their different side chains give each amino acid its individual characteristics. These differences influence how amino acids interact and how the proteins constructed from them eventually fold and function.
Around 20 standard amino acids are commonly used by the body to build proteins. They can be arranged in an enormous number of combinations, allowing the body to produce proteins with very different structures and purposes.
Amino acids can come from:
- Protein-containing foods
- The breakdown and recycling of proteins already in the body
- The body’s own production processes
- Protein or amino-acid supplements
What Do Amino Acids Do in the Body?
The most familiar role of amino acids is forming proteins, but they also participate in a wider range of biological processes.
They Build Proteins
Amino acids connect through chemical bonds known as peptide bonds. The order in which they are joined is important. A change in the sequence can affect how the chain folds and how the resulting protein behaves.
Proteins produced from amino acids include:
- Collagen
- Keratin
- Haemoglobin
- Enzymes
- Antibodies
- Muscle proteins
- Transport proteins
- Some hormones
The body does not send every amino acid from a particular food to one specific tissue. Dietary protein is digested, and the released amino acids enter a shared metabolic pool that can be used according to the body’s requirements.
They Help Form Enzymes
Many enzymes are proteins constructed from amino acids. Enzymes help control chemical reactions throughout the body, including digestion, energy metabolism and the production or breakdown of other compounds. Their function depends on their precise amino-acid sequence and three-dimensional shape.
They Contribute to Hormones and Signalling Compounds
Some hormones are proteins or peptides made from amino-acid chains. Individual amino acids can also be used as starting materials for other signalling compounds.
This does not mean that consuming more of one amino acid automatically increases the production of a particular hormone. These processes are tightly regulated and depend on many factors.
They Form Structural Proteins
Amino acids are used to create structural proteins found throughout the body. Collagen, for example, contains an unusual concentration of glycine, proline and hydroxyproline. Keratin has a different composition suited to its own structure.
The properties of a structural protein come from the amino acids present, their sequence and the way the protein chains are assembled.
They Can Be Used for Energy
Amino acids can be used as an energy source when required. However, their primary nutritional role is not identical to that of carbohydrates or fats.
Unlike fat and carbohydrate, the body does not maintain a dedicated storage reserve of excess amino acids. Amino acids that are not required for protein production or other processes can be broken down.
The nitrogen-containing part is removed and processed, while the remaining components may enter pathways connected with energy production or be converted into other compounds.
Essential and Non-Essential Amino Acids
Amino acids are commonly grouped according to whether the body can produce them.
Essential Amino Acids
Essential amino acids cannot be made by the body in sufficient quantities and must therefore be obtained through food.
The nine essential amino acids are:
| Essential amino acid | Common abbreviation |
|---|---|
| Histidine | His |
| Isoleucine | Ile |
| Leucine | Leu |
| Lysine | Lys |
| Methionine | Met |
| Phenylalanine | Phe |
| Threonine | Thr |
| Tryptophan | Trp |
| Valine | Val |
A protein’s nutritional quality depends partly on the quantities and proportions of these essential amino acids, as well as how effectively the protein is digested.
The Food and Agriculture Organization’s work on protein quality considers indispensable amino-acid patterns, digestion and metabolic use rather than judging a protein by its total weight alone.
Non-Essential Amino Acids
Non-essential amino acids can normally be produced by the body.
Examples include:
- Alanine
- Asparagine
- Aspartic acid
- Glutamic acid
- Serine
The word “non-essential” does not mean these amino acids are unimportant. It only means the body is not normally dependent on food as its sole source.
Conditionally Essential Amino Acids
Some amino acids may be described as conditionally essential. This means the body can normally make them, but requirements may exceed production under particular circumstances, such as periods of rapid growth, illness or physiological stress.
Amino acids sometimes placed in this category include:
- Arginine
- Cysteine
- Glutamine
- Glycine
- Proline
- Tyrosine
The classification can depend on age and individual circumstances. It should not be interpreted as evidence that everyone needs supplements containing these amino acids.
What Is the Difference Between Amino Acids, Peptides and Proteins?
Amino acids, peptides and proteins are related but are not interchangeable terms.
| Term | Basic meaning |
|---|---|
| Amino acid | An individual building block |
| Peptide | A relatively short chain of amino acids |
| Protein | One or more longer amino-acid chains folded into a functional structure |
There is no single universally applied chain length separating a long peptide from a small protein. The words also describe more than size because a protein’s folded structure and biological role matter.
Collagen peptides provide a useful example. Native collagen is a large structural protein composed of three chains arranged into a triple helix. Hydrolysis breaks those long chains into smaller peptides.
The resulting peptides remain constructed from amino acids, but they no longer retain the complete triple-helix structure of native collagen.
What Happens to Protein During Digestion?
Dietary proteins are too large to be absorbed intact in significant quantities. Digestion begins in the stomach and continues in the small intestine. Enzymes break proteins into progressively smaller chains, producing:
- Larger peptide fragments
- Short peptides
- Individual amino acids
These digestion products can then be absorbed through the intestinal wall.
Most dietary protein is broken down extensively, although certain dipeptides and tripeptides can also be absorbed. Once absorbed, amino acids become available for protein production and other metabolic processes.
This is why claims suggesting that an intact dietary protein travels directly to one particular body part are misleading.
What Foods Have Amino Acids?
Any food containing protein provides amino acids.
Common animal sources include:
- Meat
- Poultry
- Fish
- Eggs
- Milk
- Yoghurt
- Cheese
Common plant sources include:
- Soya beans and tofu
- Lentils
- Chickpeas
- Beans
- Peas
- Nuts
- Seeds
- Oats
- Wheat
- Quinoa
The amount and balance vary between foods. Animal proteins generally contain all nine essential amino acids in favourable proportions. Soya is also considered a complete protein, while many other individual plant proteins contain lower proportions of one or more essential amino acids. People following vegetarian or vegan diets can obtain the essential amino acids they need by consuming sufficient protein from a varied selection of plant foods. Those foods do not usually need to be carefully combined within each meal. The balance across the wider diet is more important.
What Is a Complete Protein?
A complete protein provides all nine essential amino acids in adequate proportions.
Examples commonly include:
- Eggs
- Dairy products
- Meat
- Fish
- Soya
- Quinoa
An incomplete protein provides a limited amount of one or more essential amino acids.
“Incomplete” does not mean useless or unhealthy. It describes the amino-acid profile rather than the overall quality of the food.
Eating varied protein sources can help provide a more balanced intake of essential amino acids.
What Are BCAAs?
BCAAs are branched-chain amino acids. The three BCAAs are:
- Leucine
- Isoleucine
- Valine
All three are essential amino acids.
They are commonly discussed in sports nutrition because of their involvement in muscle protein metabolism. However, muscle protein contains all the essential amino acids rather than BCAAs alone. A product containing BCAAs is not automatically a complete protein. The entire essential amino-acid profile must be considered.
Do You Need Amino-Acid Supplements?
Most people can obtain the amino acids they need from a varied diet containing sufficient protein.
Amino-acid supplements may be marketed for exercise, sleep, recovery or general wellness. However, evidence supporting one application cannot automatically be applied to every ingredient, dose or person.
Potential disadvantages of focusing on isolated amino acids include:
- Overlooking total protein intake
- Creating an unbalanced intake
- Taking more than has been studied
- Interactions with medicines or medical conditions
- Paying for something already supplied adequately by the diet
Someone with a diagnosed deficiency, restricted diet or medical condition may have different needs. In those circumstances, individual advice from a registered dietitian or qualified healthcare professional is more appropriate than selecting a supplement based on broad marketing claims.
Amino Acids in Collagen
Collagen illustrates why the amino-acid profile of a protein matters. Its characteristic composition includes high proportions of:
- Glycine
- Proline
- Hydroxyproline
These amino acids contribute to collagen’s distinctive structure. Glycine appears at every third position in the collagen sequence, while proline and hydroxyproline frequently occupy the other positions.
Collagen also contains alanine, arginine, glutamic acid, aspartic acid and smaller amounts of several essential amino acids.
However, it provides only trace amounts of tryptophan and relatively small quantities of some other essential amino acids. Collagen is therefore not considered a complete protein.
Our detailed guide to the amino acids in collagen provides the complete Beauvyn ingredient profile and explains why glycine, proline and hydroxyproline are particularly prominent.
Do Amino Acids Support the Skin?
The skin contains many proteins, including collagen and keratin, which are constructed from amino acids. Amino acids therefore have established structural roles within skin proteins. However, that does not mean consuming one individual amino acid will automatically improve skin appearance.
After digestion, the body distributes and uses amino acids according to wider metabolic needs. Outcomes can also be affected by total diet, age, health, smoking and sun exposure.
Claims about an amino acid’s biological role should be distinguished from evidence showing that a specific oral product produces a visible cosmetic result.
Does the Body Store Amino Acids?
The body maintains a circulating and cellular pool of free amino acids, but it does not have a dedicated long-term amino-acid store comparable with body fat. Body proteins are continually being created and broken down. Amino acids released through normal protein turnover can be reused.
When amino acids are present beyond current requirements, they cannot simply be stored as additional free amino acids indefinitely. Their nitrogen is removed, and the remaining components can enter other metabolic pathways. This is another reason why consuming increasingly large amounts does not necessarily produce a greater benefit.
Frequently Asked Questions
What is the main function of amino acids?
Their best-known function is forming proteins. They are also used to produce enzymes, some hormones, neurotransmitters and other nitrogen-containing compounds.
How many amino acids are there?
Twenty standard amino acids are commonly used to construct human proteins. Other modified or non-protein amino acids also exist.
How many essential amino acids are there?
There are nine essential amino acids that must be obtained through the diet.
What is the difference between essential and non-essential amino acids?
Essential amino acids must be obtained through food. Non-essential amino acids can normally be produced by the body.
Are peptides made from amino acids?
Yes. Peptides are chains of amino acids joined by peptide bonds.
Is protein made from amino acids?
Yes. Proteins contain one or more amino-acid chains arranged and folded into particular structures.
What foods contain all nine essential amino acids?
Examples include eggs, dairy products, meat, fish and soya. A varied combination of plant foods can also provide all the essential amino acids across the diet.
Do vegetables contain amino acids?
Yes. Vegetables contain some protein and therefore provide amino acids, although the amount is generally lower than in foods such as pulses, soya, meat, fish, eggs or dairy.
Is collagen an amino acid?
No. Collagen is a protein containing numerous amino acids. Glycine, proline and hydroxyproline are particularly prominent.
Is collagen a complete protein?
No. Collagen provides only trace amounts of tryptophan and relatively low amounts of several other essential amino acids.
Are amino acids and BCAAs the same?
BCAAs are one group of amino acids consisting of leucine, isoleucine and valine. Many other amino acids are not BCAAs.
Can amino acids replace food?
Amino-acid supplements do not provide the full nutritional value of whole foods and should not be treated as replacements for a balanced diet.
The Final Say
Amino acids are the smaller compounds used to create proteins. They contribute to structural proteins, enzymes, signalling compounds and many other normal biological processes. Nine essential amino acids must be obtained from food, while the body can produce the remaining non-essential amino acids under normal circumstances.
Different foods and supplements provide different amino-acid profiles. This is why the total amount of protein does not tell the whole story. A varied diet containing suitable protein sources remains the most practical way for most people to obtain a balanced range of amino acids.
