What is Isoleucine? High and low values | Lab results explained

Isoleucine is one of the three branched-chain amino acids (BCAAs) alongside both leucine and valine.

Isoleucine is a common component of proteins, peptides and hormones. Leucine is catabolized as a source of carbon for energy production during exercise in skeletal muscle.

Relative to the other two BCAAs, isoleucine is intermediate for its ability to induce muscle protein synthesis (stronger than valine, but much weaker than leucine) but is able to significantly increase glucose uptake and the usage of glucose during exercise. Isoleucine does not promote glycogen synthesis, however.

BCAAs are used for the synthesis of enzymes, transport proteins, and structural components of cells. Unlike other amino acids, BCAAs do not serve as precursors for bile acids or neurotransmitters, but are involved in control mechanisms for neurotransmitters, muscle development and repair, and blood-sugar regulation.

Isoleucine is a part of carbohydrate and fat metabolism. 

Lower levels:

– Low BCAAs are an indication of chronic depletion from low protein intake, poor digestion, or increased utilization from chronic over-exercising.

– Studies have shown that low levels of isoleucine in plasma indicate an increased need for niacin. Chronic deficiency can cause hypoglycemia, loss of muscle mass, or inability to build muscle.

– Isoleucine and the other branched chain amino acids can be low as a result of zinc deficiency (zinc dependent intestinal peptidase), protein malnutrition or other gastrointestinal dysfunctions.

– A chronic deficiency of this AA can cause hypoglycemia and related problems and loss of muscle mass or inability to build muscle.

Higher levels:

– High fasting levels may be caused by a deficiency of vitamin B6, elevated insulin levels, or excessive BCAA intake.

– Studies found that plasma BCAA levels can be associated with animal protein consumption. Dairy products and red meat contain the greatest amounts of BCAAs, although they are present in all protein-containing foods. Whey protein and egg protein supplements are other sources of BCAAs. Lowering the intake of these foods can lower the isoleucine plasma levels.

Possible treatment:

Lower your BCAA intake by focusing on a whole foods plant-based diet. Check also for sufficient vitamin B6 intake to aid metabolism.

References:

– https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6356602/

– https://www.ncbi.nlm.nih.gov/pubmed/24682914

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