Isoleucine: How It Works, Benefits, Clinical Studies And Side Effects

BCAA: Valine, Leucine, Isoleucine

What is Isoleucine?


Abbreviation: I or Ile

Isoleucine is among the three BCAAs (Branched Chain Amino Acids), all of which help in recovery of muscles after exercise.

Function: It helps in increasing muscle endurance and promotes fast recovery and healing of muscular tissue.

Ingredients uses in: Sports supplements.

Isoleucine is a branched chain alpha-amino acid which is utilized by the body in the biosynthesis of proteins. It is similar in structure to leucine, and is an essential amino acid – meaning that the human body is incapable of producing isoleucine, therefore it has to be obtained from other sources such as diet or supplements. Isoleucine is naturally microorganisms (such as bacteria) and plants. It is actively utilized in the adipose (fat) and muscular tissues for muscular recovery, as well as in the clotting of blood at the site of injury.

Benefits of Isoleucine for Body Building

Isoleucine has the following benefits for muscle building:

  • Increased muscle endurance
  • Faster muscle recovery after exercise
  • Boost in energy levels of the body
  • Regulating blood sugar levels
  • Encourages blood clotting at the site of injuryisoleucine user
  • Increased glucose tolerance, leading to a leaner body
  • Increased metabolism
  • Reduced body fat

How Does It Work?

All the three BCAAs (valine, leucine, isoleucine) help in the recovery of muscles after strenuous exercise. Isoleucine being one of them, is highly important for bodybuilders and athletes, as it helps in increasing muscular endurance for exercise, as well as helps in clotting of blood. It is broken down in the muscle cells for energy and also boosts the body’s energy by regulating sugar levels in blood. A deficiency of isoleucine triggers symptoms like that of hypoglycemia, some of which include:

  • Depression
  • Fatigue
  • Dizziness
  • Irritability
  • Headaches
  • Confusion

Other Benefits

Isoleucine does not only help in muscle building, but also in the synthesis of many structural and functional proteins, such as:

  • Antibodies – which strengthen the immune system
  • Other hormones – which help in regulation of various body mechanisms

In addition to proteins, isoleucine is also used by the body to manufacture glucose and ketone bodies.

  • When your blood sugar is low, such as during exercise, the body produces glucose from other compounds, such as amino acids (one of which is leucine), through a process called gluconeogenesis
  • Ketone bodies are also broken down by the body to produce energy. They are produced in various organs of the body, such as, the heart


three eggs in a basket

Isoleucine can be obtained from diet to get the required amount for your body. However, if you have plans for muscle building, you will have to take isoleucine supplements.

Some natural food sources of leucine are meat, lentils, eggs, chicken, seeds, soy protein, peas, fish, etc. If you have a deficiency of isoleucine, consult your doctor for the dose of isoleucine supplement.

Clinical Studies

A study (source) was conducted to evaluate the effects of BCAA on muscle loss and power in people trekking at high altitudes. According to the results of the study, BCAAs supplementation synthesizes muscular tissue, and can prevent loss of muscle mass during hypoxia (low levels of oxygen in the body).

In another study (source), resistance trained participants were provided with a 14g supplement of either:

  1. Whey protein
  2. BCAAs, or
  3. Carbohydrate placebo

The study went on for 8 weeks and all the participants also took part in a strength training routine. At the end of the study, it was found that the BCAA group had significant changes as compared to others. They had a 4 kg increase in leans mass and 2% loss in body fat.


A dose of 68-144mg/kg of body weight is considered optimal for healthy adults.

Side Effects

High levels of BCAA in blood may cause:

  • Mood swings
  • Sleep problems

A word of caution

  • People who are suffering from any kidney or liver diseases, or impaired functions, should avoid taking isoleucine as unmonitored doses may worsen these conditions.
  • For people suffering from chronic alcoholism, high levels of isoleucine may lead to liver and brain damage.
  • Consuming isoleucine supplements may interfere with surgery and post-surgery recovery. It is recommended to stop the use of isoleucine supplements two weeks prior to scheduled surgery.
  • For ALS patients, it is recommended to steer clear of isoleucine as it may cause lung failure and even death.
  • In people are suffering from branched-chain ketoaceduria, high levels of isoleucine can cause seizures and severe mental retardation.


As isoleucine is one of the three BCAAs, it is crucial for muscle growth, repair and endurance. It helps in regulating blood glucose and increases the strength of muscles by increasing muscle endurance. Isoleucine is generally taken along with leucine and valine; the two other BCAAs. The ratio of BCAAs in the body needs to be maintained, and any upset or increased levels may lead to health implications and serious damage to the body. If you want to start on isoleucine or BCAA supplements, keep the contraindications in mind, and do consult your doctor to avoid any negative health consequences of this supplement.