Leucine Supplement Side Effects
Most Americans easily get enough leucine from foods rich in this essential amino acid. Such foods include poultry, fish, meat, nuts, seeds and dairy products like yogurt and cottage cheese. Leucine supplements may increase athletic performance and muscle strength, says the Memorial Sloan Kettering Cancer Center, though more research is needed. While you can't consume enough leucine from foods to cause harmful side effects, you should use leucine supplements with caution.
Recommended Intake and Sources
Healthy adults need approximately 42 milligrams of leucine per kilogram of their body weight each day. An average man weighing 196 pounds would require about 3,733 milligrams of leucine daily, while a woman of 166.2 pounds should have around 3,166 milligrams. To avoid the possible side effects of leucine supplements, it's best to obtain the majority of the amino acid through diet. Excellent sources include turkey breast, which contains 2,076 milligrams in every 3-ounce serving, and roasted soybeans, with nearly 5,000 milligrams per cup.
- Healthy adults need approximately 42 milligrams of leucine per kilogram of their body weight each day.
- Excellent sources include turkey breast, which contains 2,076 milligrams in every 3-ounce serving, and roasted soybeans, with nearly 5,000 milligrams per cup.
Effect on B Vitamins
In 2012, a study published in the "Journal of Nutrition" reported that men taking more than 39 grams, or 39,000 milligrams, of supplemental leucine per day had an increased likelihood of experiencing harmful side effects. One of these side effects can include vitamin B-3 and vitamin B-6 deficiency since leucine interferes with the body's ability to synthesize these nutrients. Not having enough vitamin B-3 -- also known as niacin -- may cause vomiting, depression and indigestion and may increase your risk of Alzheimer's disease and high blood cholesterol. A lack of vitamin B-6, or pyridoxine, can result in memory loss, irritability and depression.
- In 2012, a study published in the "Journal of Nutrition" reported that men taking more than 39 grams, or 39,000 milligrams, of supplemental leucine per day had an increased likelihood of experiencing harmful side effects.
- A lack of vitamin B-6, or pyridoxine, can result in memory loss, irritability and depression.
Possible Impact on the Prostate
Prostate cancer cells need leucine to grow, multiply and spread, determined a "Journal of the National Cancer Institute" study published in 2013. Leucine is delivered to these cells in the body by L-type amino acid transporters. The researchers concluded that finding a way to inhibit these transporters could prevent prostate cancer cell growth by limiting the amount of available leucine. It is not known if taking supplemental leucine and significantly increasing the amount of available leucine in the body could increase your risk of prostate cancer or speed the growth of tumors in men, however.
- Prostate cancer cells need leucine to grow, multiply and spread, determined a "Journal of the National Cancer Institute" study published in 2013.
- The researchers concluded that finding a way to inhibit these transporters could prevent prostate cancer cell growth by limiting the amount of available leucine.
Interaction with Diabetes Medications
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When supplemental leucine is consumed with a source of glucose, it increases the amount of insulin your body produces and lowers your blood sugar level. Taking leucine at the same time as a diabetes medication, including insulin, may cause your blood sugar to drop too low. If you suffer from hypoglycemia -- chronic low blood sugar -- due to a medical problem or a deficiency in an enzyme or hormone, avoid taking supplemental leucine.
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- Memorial Sloan Kettering Cancer Center: Leucine
- Prostate.net: Leucine Health Benefits
- Journal of Nutrition: Determination of the Tolerable Upper Intake Level of Leucine in Adult Men
- University of Maryland Medical Center: Vitamin B-3 (Niacin)
- University of Maryland Medical Center: Vitamin B-6 (Pyridoxine)
- Journal of the National Cancer Institute: Proteins that Deliver Leucine to Prostate Cancer Cells Are Therapeutic Targets
- Metabolism: Clinical and Experimental: Leucine, When Ingested With Glucose, Synergistically Stimulates Insulin Secretion and Lowers Blood Glucose
- MedlinePlus: Hypoglycemia
- MedlinePlus: Maple Syrup Urine Disease
- U.S. Department of Agriculture: 10 - Protein and Amino Acids
- U.S. Department of Health and Human Services, U.S. Department of Agriculture. Appendix 7. Nutritional Goals for Age-Sex Groups Based on Dietary Reference Intakes and Dietary Guidelines Recommendations. 2020.
- American College of Sports Medicine. Protein Intake for Optimal Muscle Maintenance. 2015.
- Protein and Amino Acids. In: National Research Council (US) Subcommittee on the Tenth Edition of the Recommended Dietary Allowances. Recommended Dietary Allowances: 10th Edition. Washington, DC: National Academies Press (US); 1989.
- Mero A. Leucine Supplementation and Intensive Training. Sports Med. 1999;27(6):347-358. doi:10.2165/00007256-199927060-00001
- Kurpad AV, Regan MM, Raj T, Gnanou JV. Branched-Chain Amino Acid Requirements in Healthy Adult Human Subjects. J Nutr. 2006;136(1 Suppl):256S-263S. doi:10.1093/jn/136.1.256S
- Mobley CB, Haun CT, Roberson PA, et al. Effects of Whey, Soy or Leucine Supplementation with 12 Weeks of Resistance Training on Strength, Body Composition, and Skeletal Muscle and Adipose Tissue Histological Attributes in College-Aged Males. Nutrients. 2017;9(9):972. doi:10.3390/nu9090972
- Aguiar AF, Grala AP, Da Silva RA, et al. Free leucine supplementation during an 8-week resistance training program does not increase muscle mass and strength in untrained young adult subjects. Amino Acids. 2017;49(7):1255-1262. doi:10.1007/s00726-017-2427-0
- Devries MC, McGlory C, Bolster DR, et al. Leucine, Not Total Protein, Content of a Supplement Is the Primary Determinant of Muscle Protein Anabolic Responses in Healthy Older Women. J Nutr. 2018;148(7):1088-1095. doi:10.1093/jn/nxy091
- Layman DK. The Role of Leucine in Weight Loss Diets and Glucose Homeostasis. J Nutr. 2003;133(1):261S-267S. doi:10.1093/jn/133.1.261S
- Layman DK, Walker DA. Potential Importance of Leucine in Treatment of Obesity and the Metabolic Syndrome. J Nutr. 2006;136(1 Suppl):319S-323S. doi:10.1093/jn/136.1.319S
- University of Arkansas Division of Agriculture. Leucine serves an important role for health, but needs to eaten as part of a complete protein. 2015.
- American Association for the Advancement of Science. Research from Everest: Can leucine help burn fat and spare muscle tissue during exercise? 2011.
- Duan Y, Li F, Li Y, et al. The role of leucine and its metabolites in protein and energy metabolism. Amino Acids. 2016;48(1):41-51. doi:10.1007/s00726-015-2067-1
Michelle Kerns writes for a variety of print and online publications and specializes in literature and science topics. She has served as a book columnist since 2008 and is a member of the National Book Critics Circle. Kerns studied English literature and neurology at UC Davis.