Isoleucine amino acid supplement by Ray Sahelian, M.D.

L Isoleucine is one of the branched-chain amino acid which also include leucine and valine. I have not come across any human studies with isoleucine supplement taken orally by itself. Therefore, I am not sure why anyone would take an isoleucine supplement. You can purchase a combination of leucine, isoleucine and valine branched chain amino acids, a BCAA supplement. BCAA also has glutamine amino acid. If you wish to increase muscle mass, consider creatine powder.

Isoleucine health benefit
I have not seen human research regarding the health benefits of taking oral isoleucine supplements alone. An animal study shows improved blood sugar control.

Isoleucine in liver disease
Isoleucine infusion during "simulated" upper gastrointestinal bleeding improves liver and muscle protein synthesis in cirrhotic patients.
Hepatology. 2007. Department of Surgery, Academic Hospital, Maastricht University, Maastricht, The Netherlands.
Upper gastrointestinal (GI) bleeding in cirrhotic patients has a high incidence of mortality and morbidity. Postbleeding catabolism has been hypothesized to be partly due to the low biological value of hemoglobin, which lacks the essential amino acid isoleucine. The aims were to study the metabolic consequences of a "simulated" upper GI bleed in patients with cirrhosis of the liver and the effects of intravenous infusion of isoleucine. The present study investigated hepatic and portal drained viscera protein metabolism selectively in humans. The data show that hepatic and muscle protein synthesis is stimulated by improving the amino acid composition of the upper GI bleed by simultaneous intravenous isoleucine administration.

Readers ask
I saw your note about why anyone would need to take an isoleucine supplement. What about this study?
Isoleucine, a Blood Glucose-Lowering Amino Acid, Increases Glucose Uptake in Rat Skeletal Muscle in the Absence of Increases in AMP-Activated Protein Kinase Activity. The American Society for Nutritional Sciences J. Nutr. September 2005. Division of Pharmacology, Drug Safety and Metabolism, Otsuka Pharmaceutical Factory Incorporated, Naruto, Tokushima and * Department of Animal Science, Utsunomiya University, Utsunomiya, Tochigi, Japan
Leucine and isoleucine were shown to stimulate insulin-independent glucose uptake in skeletal muscle cells in vitro. In this study, we examined the effects of leucine and isoleucine on blood glucose in food-deprived rats and on glucose metabolism in skeletal muscle in vivo. Furthermore, we investigated the possible involvement of the energy sensor, 5'-AMP-activated protein kinase, in the modulation of glucose uptake in skeletal muscle, which is independent of insulin, and also in leucine- or isoleucine-stimulated glucose uptake. Oral administration of isoleucine, but not leucine, significantly decreased the plasma glucose concentration. This is the first report of isoleucine stimulating glucose uptake in rat skeletal muscle in vivo, and these results indicate that there might be a relation between the reduction in blood glucose and the increase in skeletal muscle glucose uptake that occur with isoleucine administration in rats. The alterations in glucose metabolism caused by isoleucine may result in an improvement of the availability of ATP in the absence of increases in AMP-activated protein kinase activity in skeletal muscle.
    Thanks for sending this, but I prefer seeing an actual study in humans with dosages that are reasonable to take by an average person before recommending an isoleucine supplement.