Blood & Laboratory Values

Isoleucine – Function & Diseases


The essential amino acid isoleucine is just as important for people who are not exposed to physical stress as it is for those who have to perform at their best as competitive and endurance athletes.

Isoleucine is found in every amino acid and therefore influences many bodily functions. A deficiency or excess leads to serious health problems and, in extreme cases, even to death.

What is isoleucine?

Isoleucine is a branched-chain essential amino acid that belongs to the group of BCAAs (Branched Chain Amino Acids). It is typical for these proteins that they have a characteristic branching in their structural chain.

As an essential amino acid, isoleucine cannot be synthesized by the body itself, but must be supplied through food or as a dietary supplement . Isoleucine can react basic or acidic. It occurs in varying amounts in many other amino acids and is not metabolized in the liver but transported directly to the muscles . Since it promotes the development of muscle tissue in athletes and heavily stressed people, it is also referred to as a “stress amino acid”. The organism breaks them down via the fatty acid metabolism. It is also excreted in small amounts in the urine .

Function, effect & tasks

Isoleucine, along with the other two BCAAs valine and leucine, builds muscle tissue by promoting the synthesis and storage of proteins in the muscles. 

In addition, it regenerates and maintains muscle tissue. It supplies energy in the form of glucose during heavy physical exertion . The essential amino acid regulates hormone balance and blood sugar levels by stimulating insulin release in the pancreas . It also provides the growth hormone somatotropin in sufficient quantities. Since the branched-chain protein has a strengthening effect on the immune system , it also promotes wound healing .

In the event of severe physical stress , operations and illnesses, together with leucine and valine, it reduces the breakdown of muscle tissue. Competitive athletes and the sick should therefore also consume isoleucine, valine and leucine. The same applies to people who follow a reduction diet. In certain forms of schizophrenia , phenylketonuria and cirrhosis of the liver , isoleucine improves the clinical picture.

Formation, Occurrence, Properties & Optimal Values

Since the body cannot produce isoleucine itself, it should be obtained from food or as a dietary supplement. It also makes sense to take in sufficient amounts every day, since increased stress, illness and a lot of physical exercise lead to the breakdown of the amino acid in the body. The optimal amount of isoleucine is 1.4 g per day. The daily minimum is 0.7 grams. With intensive physical exertion, the requirement increases to 5 to 10 g daily.

In order to always provide the body with a sufficient amount of isoleucine, a balanced healthy diet with legumes, nuts and chickpeas is recommended. Salmon, beef and veal also contain a lot of isoleucine. Wheat germ (1.32 g per 100 g) has the highest content, followed by peanuts (1.23 g) and tuna (1.21 g/100 g). An accidental isoleucine overdose is immediately converted into amino acids and storage fat by a healthy body. However , patients with liver and kidney diseases should consult their doctor beforehand.

Diseases & Disorders

A lack of isoleucine can lead to muscle weakness and listlessness . If the transport of the amino acid through the cell membrane is disturbed, Hartrup’s syndrome develops: the cells in the gastrointestinal tract and in the kidneys can no longer absorb the essential amino acid. 

The Hartrup syndrome shows up in symptoms such as lupus-like eczema (pellagra), increased photosensitivity of the skin, excessive or weak skin pigmentation, paroxysmal diarrhea , tremors , spasms , double vision , headaches , depressive moods, delusions , fears , etc. A high concentration of proteins can be detected in the urine of the patients. The metabolic disorder is inherited in an autosomal recessive manner and occurs with a probability of 1 to 9 in 100,000. Patients of all ages are affected.

The daily administration of 40 – 200 mg nicotinamide and adherence to a protein-rich diet are recommended as therapy. The neurological-psychiatric symptoms are treated by the appropriate specialists. An excess of isoleucine can lead to the occurrence of hyperaminoaciduria, a metabolic disease in which there is increased excretion of amino acids in the urine. In patients with liver damage or phenylketonuria, the level of isoleucine in the blood is increased up to 10-fold. Maple syrup disease is a very rare metabolic disease also known as valine-leucine isoleucinuria or leucinosis. Patients with this disease have a genetic enzyme defect.

The enzyme alpha-keto acid dehydrogenase is no longer able to break down the amino acid in the blood. Isoleucine, leucine and valine are excreted in the urine, which smells like maple syrup because of their decomposition products. The autosomal recessive inherited disease occurs with a probability of 1:100,000 and shows up in newborns with breathing disorders, vomiting , unconsciousness , epileptic seizures and – if not treated in time – leads to the death of the child. In patients with maple syrup disease, an excessively high level of isoleucine, valine, leucine, keto and hydroxy acids can be detected in all organs and body fluids (overacidification of the organism).

For first aid, the infant is given glucose and complex sugars in an infusion solution. In addition, he does not receive protein-rich food for two days. In extreme cases, blood washing may be indicated. In order to prevent further metabolic imbalances, the patient must adhere to a lifelong low-protein diet.

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.