Amino acids are organic compounds composed of nitrogen, carbon, hydrogen and oxygen, along with a variable side chain group.
Your body needs 20 different amino acids to grow and function properly. Though all 20 of these are important for your health, only nine amino acids are classified as essential (1Trusted Source).
These are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.
Unlike nonessential amino acids, essential amino acids can’t be made by your body and must be obtained through your diet.
The nine essential amino acids perform a number of important and varied jobs in your body:
Phenylalanine: Phenylalanine is a precursor for the neurotransmitters tyrosine, dopamine, epinephrine and norepinephrine. It plays an integral role in the structure and function of proteins and enzymes and the production of other amino acids (4).
Valine: Valine is one of three branched-chain amino acids, meaning it has a chain branching off to one side of its molecular structure. Valine helps stimulate muscle growth and regeneration and is involved in energy production (5).
Threonine: Threonine is a principal part of structural proteins such as collagen and elastin, which are important components of the skin and connective tissue. It also plays a role in fat metabolism and immune function (6).
Tryptophan: Though often associated with causing drowsiness, tryptophan has many other functions. It’s needed to maintain proper nitrogen balance and is a precursor to serotonin, a neurotransmitter that regulates your appetite, sleep and mood (7).
Methionine: Methionine plays an important role in metabolism and detoxification. It’s also necessary for tissue growth and the absorption of zinc and selenium, minerals that are vital to your health (8).
Leucine: Like valine, leucine is a branched-chain amino acid that is critical for protein synthesis and muscle repair. It also helps regulate blood sugar levels, stimulates wound healing and produces growth hormones (9).
Isoleucine: The last of the three branched-chain amino acids, isoleucine is involved in muscle metabolism and is heavily concentrated in muscle tissue. It’s also important for immune function, hemoglobin production and energy regulation (10).
Lysine: Lysine plays major roles in protein synthesis, hormone and enzyme production and the absorption of calcium. It’s also important for energy production, immune function and the production of collagen and elastin (11).
Histidine: Histidine is used to produce histamine, a neurotransmitter that is vital to immune response, digestion, sexual function and sleep-wake cycles. It’s critical for maintaining the myelin sheath, a protective barrier that surrounds your nerve cells.
Since your body cannot produce essential amino acids, they must be provided through your diet.
Fortunately, many foods are rich in essential amino acids, making it easy to meet your daily needs.
The US recommended daily allowances per 2.2 pounds (1 kg) of body weight for the nine essential amino acids are (29):
Histidine: 14 mg
Isoleucine: 19 mg
Leucine: 42 mg
Lysine: 38 mg
Methionine (+ the non-essential amino acid cysteine): 19 mg
Phenylalanine (+ the non-essential amino acid tyrosine): 33 mg
Threonine: 20 mg
Tryptophan: 5 mg
Valine: 24 mg
9 Important Functions of Protein in Your Body
Protein is crucial to good health.
In fact, the name comes from the Greek word proteos, meaning “primary” or “first place.”
Proteins are made up of amino acids that join together to form long chains. You can think of a protein as a string of beads in which each bead is an amino acid.
There are 20 amino acids that help form the thousands of different proteins in your body.
Proteins do most of their work in the cell and perform various jobs.
Here are 9 important functions of protein in your body.
1. Growth and Maintenance
Your body needs protein for growth and maintenance of tissues.
Yet, your body’s proteins are in a constant state of turnover.
Under normal circumstances, your body breaks down the same amount of protein that it uses to build and repair tissues. Other times, it breaks down more protein than it can create, thus increasing your body’s needs.
This typically happens in periods of illness, during pregnancy and while breastfeeding (1Trusted Source, 2Trusted Source, 3Trusted Source).
People recovering from an injury or surgery, older adults and athletes require more protein as well (4Trusted Source, 5Trusted Source, 6Trusted Source).
SUMMARY
Protein is required for the growth and maintenance of tissues. Your body’s protein needs are dependent upon your health and activity level.
2. Causes Biochemical Reactions
Enzymes are proteins that aid the thousands of biochemical reactions that take place within and outside of your cells (7Trusted Source).
The structure of enzymes allows them to combine with other molecules inside the cell called substrates, which catalyze reactions that are essential to your metabolism (8Trusted Source).
Enzymes may also function outside the cell, such as digestive enzymes like lactase and sucrase, which help digest sugar.
Some enzymes require other molecules, such as vitamins or minerals, for a reaction to take place.
Bodily functions that depend on enzymes include (9Trusted Source):
Digestion
Energy production
Blood clotting
Muscle contraction
Lack or improper function of these enzymes can result in disease (10Trusted Source).
SUMMARY
Enzymes are proteins that allow key chemical reactions to take place within your body.
3. Acts as a Messenger
Some proteins are hormones, which are chemical messengers that aid communication between your cells, tissues and organs.
They’re made and secreted by endocrine tissues or glands and then transported in your blood to their target tissues or organs where they bind to protein receptors on the cell surface.
Hormones can be grouped into three main categories (11Trusted Source):
Protein and peptides: These are made from chains of amino acids, ranging from a few to several hundred.
Steroids: These are made from the fat cholesterol. The sex hormones, testosterone and estrogen, are steroid-based.
Amines: These are made from the individual amino acids tryptophan or tyrosine, which help make hormones related to sleep and metabolism.
Protein and polypeptides make up most of your body’s hormones.
Some examples include (12Trusted Source):
Insulin: Signals the uptake of glucose or sugar into the cell.
Glucagon: Signals the breakdown of stored glucose in the liver.
hGH (human growth hormone): Stimulates the growth of various tissues, including bone.
ADH (antidiuretic hormone): Signals the kidneys to reabsorb water.
ACTH (adrenocorticotropic hormone): Stimulates the release of cortisol, a key factor in metabolism.
SUMMARY
Amino acid chains of various lengths form protein and peptides, which make up several of your body’s hormones and transmit information between your cells, tissues and organs.
4. Provides Structure
Some proteins are fibrous and provide cells and tissues with stiffness and rigidity.
These proteins include keratin, collagen and elastin, which help form the connective framework of certain structures in your body (13Trusted Source).
Keratin is a structural protein that is found in your skin, hair and nails.
Collagen is the most abundant protein in your body and is the structural protein of your bones, tendons, ligaments and skin (14Trusted Source).
Elastin is several hundred times more flexible than collagen. Its high elasticity allows many tissues in your body to return to their original shape after stretching or contracting, such as your uterus, lungs and arteries (15Trusted Source).
SUMMARY
A class of proteins known as fibrous proteins provide various parts of your body with structure, strength and elasticity.
5. Maintains Proper pH
Protein plays a vital role in regulating the concentrations of acids and bases in your blood and other bodily fluids (16Trusted Source, 17Trusted Source).
The balance between acids and bases is measured using the pH scale. It ranges from 0 to 14, with 0 being the most acidic, 7 neutral and 14 the most alkaline.
Examples of the pH value of common substances include (18):
pH 2: Stomach acid
pH 4: Tomato juice
pH 5: Black coffee
pH 7.4: Human blood
pH 10: Milk of magnesia
pH 12: Soapy water
A variety of buffering systems allows your bodily fluids to maintain normal pH ranges.
A constant pH is necessary, as even a slight change in pH can be harmful or potentially deadly (19Trusted Source, 20Trusted Source).
One way your body regulates pH is with proteins. An example is hemoglobin, a protein that makes up red blood cells.
Hemoglobin binds small amounts of acid, helping to maintain the normal pH value of your blood.
The other buffer systems in your body include phosphate and bicarbonate (16Trusted Source).
SUMMARY
Proteins act as a buffer system, helping your body maintain proper pH values of the blood and other bodily fluids.
6. Balances Fluids
Proteins regulate body processes to maintain fluid balance.
Albumin and globulin are proteins in your blood that help maintain your body’s fluid balance by attracting and retaining water (21Trusted Source, 22Trusted Source).
If you don’t eat enough protein, your levels of albumin and globulin eventually decrease.
Consequently, these proteins can no longer keep blood in your blood vessels, and the fluid is forced into the spaces between your cells.
As the fluid continues to build up in the spaces between your cells, swelling or edema occurs, particularly in the stomach region (23Trusted Source).
This is a form of severe protein malnutrition called kwashiorkor that develops when a person is consuming enough calories but does not consume enough protein (24Trusted Source).
Kwashiorkor is rare in developed regions of the world and occurs more often in areas of starvation.
SUMMARY
Proteins in your blood maintain the fluid balance between your blood and the surrounding tissues.
7. Bolsters Immune Health
Proteins help form immunoglobulins, or antibodies, to fight infection (25Trusted Source, 26Trusted Source).
Antibodies are proteins in your blood that help protect your body from harmful invaders like bacteria and viruses.
When these foreign invaders enter your cells, your body produces antibodies that tag them for elimination (27Trusted Source).
Without these antibodies, bacteria and viruses would be free to multiply and overwhelm your body with the disease they cause.
Once your body has produced antibodies against a particular bacteria or virus, your cells never forget how to make them.
This allows the antibodies to respond quickly the next time a particular disease agent invades your body (28Trusted Source).
As a result, your body develops immunity against the diseases to which it is exposed (29Trusted Source).
SUMMARY
Proteins form antibodies to protect your body from foreign invaders, such as disease-causing bacteria and viruses.
8. Transports and Stores Nutrients
Transport proteins carry substances throughout your bloodstream — into cells, out of cells or within cells.
The substances transported by these proteins include nutrients like vitamins or minerals, blood sugar, cholesterol and oxygen (30Trusted Source, 31Trusted Source, 32Trusted Source).
For example, hemoglobin is a protein that carries oxygen from your lungs to body tissues. Glucose transporters (GLUT) move glucose to your cells, while lipoproteins transport cholesterol and other fats in your blood.
Protein transporters are specific, meaning they will only bind to specific substances. In other words, a protein transporter that moves glucose will not move cholesterol (33Trusted Source, 34Trusted Source).
Proteins also have storage roles. Ferritin is a storage protein that stores iron (35Trusted Source).
Another storage protein is casein, which is the principal protein in milk that helps babies grow.
SUMMARY
Some proteins transport nutrients throughout your entire body, while others store them.
9. Provides Energy
Proteins can supply your body with energy.
Protein contains four calories per gram, the same amount of energy that carbs provide. Fats supply the most energy, at nine calories per gram.
However, the last thing your body wants to use for energy is protein since this valuable nutrient is widely used throughout your body.
Carbs and fats are much better suited for providing energy, as your body maintains reserves for use as fuel. Moreover, they’re metabolized more efficiently compared to protein (36Trusted Source).
In fact, protein supplies your body with very little of its energy needs under normal circumstances.
However, in a state of fasting (18–48 hours of no food intake), your body breaks down skeletal muscle so that the amino acids can supply you with energy (37Trusted Source, 38Trusted Source).
Your body also uses amino acids from broken-down skeletal muscle if carbohydrate storage is low. This can occur after exhaustive exercise or if you don’t consume enough calories in general (39Trusted Source).
SUMMARY
Protein can serve as a valuable energy source but only in situations of fasting, exhaustive exercise or inadequate calorie intake.
The Bottom Line
Protein has many roles in your body.
It helps repair and build your body’s tissues, allows metabolic reactions to take place and coordinates bodily functions.
In addition to providing your body with a structural framework, proteins also maintain proper pH and fluid balance.
Finally, they keep your immune system strong, transport and store nutrients and can act as an energy source, if needed.
Collectively, these functions make protein one of the most important nutrients for your health.