Isoleucine: Definition, Structure, Function, Benefits, Deficiency, Supplements and Toxicity

It is an amino acid that is found in most proteins and is essential in the human diet.

Along with threonine, isoleucine is one of the two common amino acids that has a chiral side chain; that is, one that is not superimposable in its mirror image.

With a hydrocarbon side chain, isoleucine is classified as a hydrophobic amino acid.

Isoleucine is similar to leucine and valine in being a branched chain amino acid and whose accumulation in the blood and urine, due to a particular deficiency of the enzyme, causes the serious metabolic disorder, known as the urinary tract disease. Maple syrup .

In humans, the L isomer of isoleucine is one of the 20 standard amino acids common in animal proteins and is required for normal functioning in humans.

Valine is also classified as an “essential amino acid”, since it can not be synthesized by the human body from other compounds through chemical reactions and, therefore, must be absorbed with the diet.

People have a personal responsibility to show discipline in their eating habits to obtain adequate amounts of the essential amino acids.

In the case of isoleucine, this means including in the diet foods such as eggs, chicken, soy, cottage cheese, milk, piyal seeds, cashews, cereals, etc.

The importance of diet is particularly important in the case of those suffering from metabolic deficiency disorder (maple syrup urine disease), in order to obtain the minimum levels of isoleucine without consuming too much to avoid the symptoms of the illness.

The precision and complex coordination in the universe is revealed in the role of isoleucine in proteins.

The structure of isoleucine makes it important for the correct folding of proteins, whose functionality depends on the ability to fold in a precise three-dimensional shape.

The three-letter isoleucine code is Ile, its one-letter code is I, and its systematic name is 2-amino-3-methylpentanoic acid (IUPAC-IUB 1983).


In biochemistry, the term amino acid is often used to refer specifically to alpha amino acids, those amino acids in which the amino and carboxylate groups are attached to the same carbon, the so-called α-carbon.

The general structure of these alpha amino acids is:

  • R | H2N-C-COOH | H

Where R represents a specific side chain for each amino acid.

Most amino acids are found in two possible optical isomers, called D and L.

The L amino acids represent the vast majority of the amino acids found in proteins. They are called proteinogenic amino acids.

As the name “proteinogenic” (literally, protein building) suggests, these amino acids are encoded by the standard genetic code and participate in the process of protein synthesis.

However, isoleucine is one of the two common amino acids (along with threonine) that has a chiral side chain.

Four stereoisomers of isoleucine are possible, including two possible diastereomers of L-isoleucine.

However, the isoleucine present in nature exists in a specific form, (2S, 3S) -2-amino-3-methylpentanoic acid.

Only this form is involved in the synthesis of proteins.

A stereoisomer has molecules with the same chemical formula and whose atomic connectivity is the same, but whose atomic arrangement in space is different.

A diastereomer are two stereoisomers that are not mirror images of each other.

The chemical formula of isoleucine is CH2-CH3-CH (CH3) -CH, or more generally C6H13NO2 (IUPAC-IUB 1983).

Isoleucine is an isomer, which has the same chemical formula but with a different arrangement of atoms.

Like leucine and valine, isoleucine has large hydrophobic aliphatic side chains.

Its molecules are rigid, and their mutual hydrophobic interactions are important for the correct folding of proteins, these amino acids tend to be located within the protein molecule.

Generally, isoleucine is attracted by similar hydrophobic side chains, such as leucine, valine, tryptophan and phenylalanine.

The functionality of the protein is determined by its folding in a precise three-dimensional configuration.

Maple syrup urine disease

Maple syrup urine disease (MUSD) is an autosomal recessive (hereditary) metabolic disorder of amino acid metabolism.

It is also called branched chain ketoaciduria.

This amino acid acidopathy is due to a deficiency of the branched-chain metabolic enzyme α-ketoacid dehydrogenase that leads to an accumulation of the branched-chain amino acids isoleucine, leucine and valine in the blood and urine.

MSUD is characterized by sweet-smelling urine similar to that of maple syrup.

Babies with this disease appear healthy at birth, but if they do not receive treatment they suffer severe brain damage and eventually die.

Due to a genetic bottleneck effect, MSUD has a much higher prevalence in children of Amish and Mennonite descent.

From early childhood, the condition is characterized by poor nutrition, vomiting, lack of energy (lethargy), seizures and mental health problems.

The urine of the affected babies has a distinctive sweet smell, much like the burnt candy that gives the condition its name.

Treatment of MSUD, such as diabetes, requires careful control of blood chemistry and includes both a special diet and frequent tests.

A diet with minimum levels of the amino acids isoleucine, leucine and valine must be maintained to prevent neurological damage.

In general, patients or parents of patients are assisted by a doctor or dietitian. This diet must be strictly and permanently complied with.

However, with proper treatment, those affected can live a healthy and normal life and not suffer the severe neurological damage that characterizes the disease when it is not treated.



One of the main functions of isoleucine is proteinogenesis in the body, which means that it is a building block for the proteins that your body’s cells produce.

It can not make the structural and functional proteins on which your body depends (including the protein that makes up the muscle, the antibodies used by your immune system and a variety of hormones) without isoleucine.

Isoleucine is an essential amino acid, which means you must consume it, since the body can not make it from other molecules.


Another important use of isoleucine in the body is the production of energy.
Isoleucine is broken down into a molecule called acetyl-CoA, which is the same molecule that is formed as it breaks down sugars.

Then burn more acetyl-CoA to produce carbon dioxide, oxygen and a large amount of energy.

It can also produce fat from acetyl-CoA, which means that excess isoleucine in the diet, like other nutrients that provide excess energy, can cause the storage of body fat.

Other uses:

You can also use isoleucine to create two other types of molecules: glucose bodies and ketone.

Glucose, or sugar in your blood, usually comes from carbohydrates in your diet.

However, if you have too little sugar in your blood, your cells participate in a process called gluconeogenesis.

You can not get glucose from fats, but you can do it from some amino acids, including isoleucine.

Ketone bodies are energy-providing molecules that are commonly produced in some organs of the body, including the heart.

Benefits of isoleucine

Better physical performance:

Athletes use this amino acid to reduce the degradation of muscles and proteins during intense physical exercise and to improve exercise performance.

In addition, it is used as fuel by muscle cells, preventing other essential amino acids from burning.

This is one of the important reasons why it is recommended to eat certain foods before your training.

Promotes healthy growth:

This amino acid is good for teenagers and children who are growing because it is essential for healthy growth.

More importantly, supplemental doses of this amino acid can be very useful in promoting tissue repair after trauma or surgery.


Soy products:

Soy products offer a unique source of protein because they are the only plant-based foods that contain nutritionally complete proteins.

All soy proteins provide all the essential amino acids that your body can not produce on its own and must obtain from your daily diet.

Soy protein isolate, a concentrated form of soy protein found in protein supplements and in meat and cheese substitutes, provides 1.9 g of leucine and 1.5 g of isoleucine for every 1 oz. , making this soy product one of the richest food sources of branched chain amino acids.

However, soy milk and tofu, each contain less than 0.2 g of leucine and isoleucine per ounce.

Fish and meat:

Meats and sins contain many branched chain amino acids since they are nutritionally complete proteins.

At 1 ounce a serving of steak provides almost 0.7 g of leucine and 0.4 g of isoleucine, and the same amount of roast pork provides a little less leucine and the same amount of isoleucine.

Tuna is also abundant in these amino acids, with 0.5 g of leucine and 0.3 g of isoleucine per ounce.

Roast chicken and roast turkey contain 0.4 g of leucine and almost 0.3 g of isoleucine in 1 oz.

Eggs and dairy products:

The content of these amino acids in cheddar cheese is very similar to that of meat, since each contains 0.7 and 0.4 g of leucine and isoleucine, respectively, per ounce.

Another rich source of amino acids is low-fat cottage cheese, since it contains 0.4 g of leucine and 0.2 g of isoleucine in each ounce.

Ounce per ounce, the eggs contain a similar amount of branched chain amino acids like cottage cheese, with most of these nutrients located in the egg white.

In comparison, milk and yogurt offer 0.2 g of leucine and 0.1 g of isoleucine per ounce.


Legumes do not provide nutritionally all the proteins necessary for their diet although they are relatively rich in them.

However, they do offer moderate amounts of branched-chain amino acids.

Lentils, black beans and pinto beans provide somewhat less than 0.2 g of leucine and almost 0.1 g of isoleucine per ounce.

While most animal protein sources provide a greater amount of branched-chain amino acids than plant sources of protein, legumes contain a good amount of these nutrients in a high-fiber, low-fat package.

Isoleucine deficiency

Isoleucine has been found to be deficient in people suffering from many different mental and physical disorders.

A deficiency of isoleucine can cause symptoms similar to those of hypoglycemia , for example, in his deficiency, a person may experience confusion, irritability, fatigue, depression , dizziness, headaches, etc.


When the body shows symptoms of isoleucine deficiency and it can not be covered with protein sources, it is likely that your doctor or dietitian recommends you take supplements that contain this amino acid.

Since isoleucine is a BCAA (branched chain amino acid), it is best to take it together with leucine and valine.

Isoleucine supplements can occur in different forms, such as tablets, soft gels and even liquids.

It may take several months before you begin to notice significant changes in isoleucine deficiency.

Just take your time, eat a healthy diet and take supplements according to the instructions.

Isoleucine, speaking in practical terms, is likely to be just a good supplement to buy when you want to increase glucose absorption.

It is surpassed by leucine to induce the synthesis of muscle proteins and surpassed by HMB to reduce muscle protein degradation, but it overtakes both agents and valine in the increase of glucose uptake in skeletal muscle.

As efficacy has been observed with 0.3-0.45 g / kg in rats (the latter being the maximum dose, which increases further and does not do anything else because it is not absorbed more), the recommended dosage range is of 48-72 mg / kg (for a person of 150 pounds, that is, the dose could vary between 3.3 and 4.9 g per day).

Isoleucine can be found in branched-chain amino acids (in which case, the proportion indicated on the label should be investigated and BCAAs are dosed accordingly) and in food products.

Since isoleucine in food products is also bioactive, the supplemental doses of isoleucine taken with meals may be lower (ie, if you consume a meal with 50 g of protein containing 4 g of isoleucine, you will no longer need a dose of 10.8 g and will be enough with 6.8 g).


It is possible to experience an overdose of isoleucine if you are not careful.

There are enzymes inside your body that are responsible for breaking down the isoleucine. If they are not enough to metabolize it, then this amino acid can accumulate to dangerous levels.

This can cause a condition called branched-chain ketoaciduria , commonly called maple syrup urine disease.