Isoleucine is an amino acid that is required for numerous blood-related processes; including the regulation of blood sugar and energy levels as well as hemoglobin formation. In association with leucine and valine, isoleucine is categorized as one of the branched-chain amino acids (BCAAs). All three of these amino acids are considered essential in human nutrition, and are needed to maintain the health of muscular tissues throughout the human body.
BCAAs also enhance and preserve glycogen stores in our skeletal muscles.  This is of great importance because muscle glycogen is instrumental in performing daily physical processes. Readily converted to energy by the body, glycogen is the primary carbohydrate energy source stored in muscle.
The members of the branched-chain amino acid family constitute nearly seventy percent of all bodily proteins. They provide constant structural and functional consistency within human biology.
Almonds, cashews, chicken, chickpeas, eggs, fish, lentils, liver, meat, rye, most seeds, and soy proteins are foods among the highest in isoleucine bioavailability. Serving sizes below are based upon 100 grams of a given food source and are expressed in milligrams, representing the amount of isoleucine contained.
|2180||Leavening agents, yeast, baker’s, active dry|
|Vegetables and Vegetable Products|
|3210||Seaweed, spirulina, dried|
|Nut and Seed Products|
|2160||Seeds, sesame flour, low-fat|
|1800||Seeds, cottonseed flour, low fat (glandless)|
|1770||Seeds, cottonseed meal, partially defatted (glandless)|
|Legumes and Legume Products|
|4250||Soy protein isolate|
|4250||Soy protein isolate, potassium type|
|2940||Soy protein concentrate|
|2380||Tofu, dried-frozen (koyadofu)|
|2380||Tofu, dried-frozen (koyadofu), prepared with calcium sulfate|
|2260||Soy flour, low-fat|
|1920||Soybeans, mature seeds, dry roasted|
|1840||Peanut flour, defatted|
|1770||Soybeans, mature seeds, raw|
|Finfish and Shellfish Products|
|2900||Fish, cod, Atlantic, dried and salted|
|1760||Chicken, broilers or fryers, breast, meat only, cooked, fried|
|1740||Chicken, stewing, light meat, meat only, cooked, stewed|
|1800||Pork, cured, bacon, cooked, broiled, pan-fried or roasted|
|1800||Pork, cured, bacon, cooked, pan-fried|
|Lamb, Veal, and Game Products|
|1810||Veal, leg (top round), separable lean only, cooked, braised|
|1780||Veal, leg (top round), separable lean and fat, cooked, braised|
|Sausages and Luncheon Meats|
|2210||Chorizo, pork and beef|
|Dairy and Egg Products|
|4580||Egg, white, dried|
|2580||Egg, whole, dried|
|2200||Cheese, parmesan, shredded|
|2190||Milk, dry, nonfat, regular, without added vitamin A|
|2190||Milk, dry, nonfat, regular, with added vitamin A|
|2070||Milk, buttermilk, dried|
|1890||Cheese, parmesan, hard|
Isoleucine (along with the two other branched-chain aminos) has been classified in research as providing no significant biological role, other than its incorporation into specific enzymes and proteins. This finding may prove true on a macro scale, but there remain specific tasks delegated by isoleucine in the body that are of great importance.
As previously mentioned, isoleucine is metabolized within muscular tissues and is necessary in the formation of hemoglobin, and in the stabilization of blood sugar and energy levels. Isoleucine is also an integral component in blood-clot formation. Absent or inadequate levels of isoleucine in the body may result in hypoglycemic-like symptoms.
Isoleucine may also enhance energy, increase endurance, and most importantly, serve as an aid in the healing and repair of muscle tissue. Therapeutic dosages may be especially beneficial for post-operative patients; alleviating muscular wasting and fostering healing. Isoleucine has been used in persons suffering from blunt trauma or burn injuries as well.
The nutritional supplementation of branched-chain amino acids (isoleucine, leucine and valine) remains popular among body builders and athletes. Aerobic, anaerobic, and strength training all require an increase in protein consumption because of the stressors induced by rigorous physical exercise.  During periods of elevated heart rate, BCAAs can be used for increased energy production. Studies have shown that nearly ten percent of the total energy expenditure produced during elongated physical activity may be directly provided by this group of essential amino acids.
Blood plasma levels may also be affected by the dietary supplementation of isoleucine. Abnormalities in the plasma amino acid pool can be corrected by high protein supplements containing isoleucine, leucine, and valine (BCAAs). This may prove useful for persons suffering from Chronic Renal Failure (CRF). Patients receiving hemodialysis (procedure for removing metabolic waste products or toxic substances from the bloodstream by dialysis) as a result of this condition often exhibit extreme deficiencies of these particular amino acids.
A recent study evaluated the effect of a balanced protein supplement on plasma levels of isoleucine, leucine, and valine in hemodialysis patients. Findings concluded that plasma BCAA levels were elevated and maintained throughout the sixth month trial period. In fact, the BCAA content in blood remained elevated nearly one month after the termination of protein supplementation on subjects.; some seven months total.  Doctors attributed the success of this study to the balanced amino acid content found within the ‘adequate’ protein supplement being administered. More research is necessary to accurately assess isoleucine’s benefit in persons receiving hemodialysis.
The established Recommended Daily Allowance (RDA) for isoleucine:
|Requirement - mg. per kg. of body weight|
|Amino acid||Infant 3 - 6 mo.||Child 10 - 12 yr.||Adults|
|Histidine||33||not known||not known|
|S-containing amino acids||45||22||10|
|Aromatic amino acids||132||22||16|
In addition, the U.S. National Academy of Sciences recommends that healthy people achieve .36 grams of highly bioavailable protein for each pound of bodyweight - equaling 0.8 grams of protein, per kilogram of bodyweight.
Deficiencies of isoleucine are often times documented in persons deficient in all dietary proteins. Individuals suffering from mental and physical disorders have also been proven to be deficient in this nutrient. Signs of an insufficiency of isoleucine may mimic hypoglycemia, exhibiting symptoms such as; headaches, dizziness, fatigue, depression, confusion, and irritability.
To date, excessive intakes of isoleucine have not been associated with any adverse health conditions, other than elevation in the frequency of urination.
Note: An inborn error exists in a small percentage of individuals called “maple syrup disease.” This genetic metabolism disorder is characterized by the buildup of metabolites in the urine. It is often times evaluated in infancy by medical practitioners. Isoleucine should be avoided in persons suffering from this condition.
1. Blomstrand E, Ek S, Newsholme EA. Influence of ingesting a solution of branched-chain amino acids on plasma and muscle concentrations of amino acids during prolonged submaximal exercise. Nutrition 1996;12:485-90.
2. Nutrition Data. “999 Foods; Highest in Isoleucine.” (2004) http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml
3. Lemon, Peter. Is increased dietary protein necessary or beneficial for individuals with a physically active lifestyle? Nutr Rev (1996) 54: S169-S175.
4. Vuzelov E, Krivoshiev S, Ribarova F, Boyadjiev N. Plasma levels of branched-chain amino acids in patients on regular hemodialysis before and after including a high-protein supplement in their diet. Folia Med (Plovdiv) 1999; 41:19-22.
5. Zest for life information page. “RDA of amino acids.” (1999-2003) http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml (14 Sept. 2004).