Leucine: Is It Good For Muscle Growth?

AminoAcidProducts | August 08, 2020 | Amino Acids

Leucine is one of the essential amino acids. Essential means your body can’t synthesize or produce using existing hormones and organic chemicals. The word Leucine came from the Greek word “Leukos” which means white. Leucine is a popular supplement among bodybuilders but the question is – Is that good for building muscles?

What Are The Functions of Leucine?

Leucine serves these functions:

  • Prevent muscle loss and protein breakdown. When you get older, your skeletal muscles undergo a gradual decline that causes decreased stamina and weakness that leads to declined physical activity. A study from the clinical nutrition published by the University of Texas’ department of internal medicine reported that leucine improved muscle development in older adults who consumed a recommended protein amount per meal. (1)
  • Helps in building muscles. Leucine is popular among bodybuilders as it may help trigger muscle growth. However, the research concluded a mix of results that leucine is only effective if mixed when used with other amino acids instead of being used alone. One way to maximize leucine efficacy is to eat other protein foods and take other essential amino acids (2).
  • Helps in losing fats – Leucine may have a positive effect on losing fats. The University of Sao Paulo and its department of food science and experimental nutrition reported that rats fed with a low leucine dosage for six weeks. (3). A similar study from the 2015 review of nutrients showed that the amino acid decreased the fat buildup and prevented obesity. (4)
  • Increase insulin levels by increasing the oxidation of glutamate into a-ketoglutarate and ATP production.
  • Regulate blood sugar – Leucine may reduce the incidence of hyperglycemia and its related symptoms such as increased thirst, fatigue, kidney problems, increased skin infections, and nerve damage. A study described that leucine taken with glucose aided in decreasing blood sugar levels and stimulating insulin secretion (5). Another related study from a vitro study from China reported that leucine facilitated glucose uptake and insulin signaling that all helped in checking blood sugar levels (6).
  • Lower cholesterol levels – A study shows that supplementing with leucine reduces aortic atherosclerotic lesion. This is due to the improved plasma lipid profile and reduced systemic inflammation.
  • Benefits muscles – A study from the University of Illinois and its department of food science and Human nutrition reported that taking leucine after bodybuilding can stimulate protein production and muscle recovery. (7) Further, a study suggested that leucine switches on mTOR or Mammalian target of rapamycin – a protein kinase or that regulates cell growth and protein synthesis in response to energy levels, nutrients, and growth factors.
  • Prevents symptoms associated with hypoglycemia such as dizziness, headaches, depression, fatigue, irritability, and confusion.
  • Provides medical usage. A medical report from the Medical Reports Today suggested that the amino acid can stave off muscle loss because of aging.
  • Benefits some brain functions. Leucine belongs to BCAAs that pain-relieving and calming effects. BCAA may reverse or treat hepatic encephalopathy that is a condition related to spleen disease and alcoholism.

Is there a leucine overdose?

  • Ammonia excess – Too much leucine supplements can lead to ammonia build in the body. When that happens, ammonia can cause organ failure and tissue damage. Kidneys and liver are sensitive to ammonia toxicity because they aid in removing excess in the bloodstream.
  • Gastrointestinal problems – High doses of leucine can lead to gastrointestinal problems when dosages above 15 grams were taken. include diarrhea, nausea, stomach, and vomiting.
  • Hypoglycemia – Hypoglycemia refers to a low blood sugar level. Excessive leucine intake can decrease blood sugar levels because of the amino acid’s ability to stimulate the pancreas to make insulin. Hypoglycemia symptoms include hunger, anxiety, sweating, and shakiness.
  • Pellagra – Pellagra is a vitamin deficiency disease caused by niacin deficiency. Symptoms include sunlight sensitivity. To counteract leucine-induced pellagra, you can take vitamin B-6 supplements.

What is a BCAA?

BCAA stands for branched-chain amino acids that comprise the protein building blocks. BCAA comprises isoleucine, leucine, and valine.

What are good food sources?

Foods rich in leucine are the following:

Parmesan cheese Shellfish
Cream cheese Beef
Wheat germ Tuna
White beans Haddock
Peanuts Turkey breast
Raw and fresh egg white Venison
Soy protein Lentils
Oats Sesame seeds
Dried spirulina Cottage Cheese

What are the other concerns with leucine intake?

Pregnant women and people with maple syrup urine disease (MSUD) may not take leucine supplements due to possible adverse effects. The same for isoleucine and valine.

What is the efficacy of leucine for muscle growth?

According to some internet resources, leucine is effective for building muscles when taken with other amino acid supplements and protein-rich foods. BCAA supplements are important when you have one of the amino acid deficiency but if you’re getting them from food, the supplements could be wasted. Another internet source concluded that leucine only works for a short term and that studies that describe the amino acid efficacy were made from the indirect measures of the body composition changes.

The verdict: is leucine for muscle growth effective? Leucine with other BCAA may or may not work depending on how you work out and what kinds of food you eat. Building muscles take time and a lot of effort to produce efficacy. It’s best to think with healthy skepticism when you face a lot of claims that promise quick and effective muscle growth by just using leucine alone.

How to make leucine work for you?

  • Take leucine with other BCAA supplements
  • Eat protein-rich foods
  • Take leucine with isoleucine and valine supplements
  • Take leucine in moderate amounts

Is Leucine Good for Building Muscles?

To confirm the absolute efficacy of leucine needs further clinical study and trials among controlled groups. Such a study should prove beyond a reasonable doubt that leucine is effective in building muscles. On the other hand, numerous studies confirmed that leucine showed promising positive effects on muscles while some scientific journals and articles told that leucine needs to be consumed with other amino acids and protein foods for efficacy. Third, another source cast doubt about the efficacy of leucine. The bottom line is that take leucine in moderation and when in doubt consult a health professional or dietician.


  1. Casperson, Shanon L, et al. “Leucine Supplementation Chronically Improves Muscle Protein Synthesis in Older Adults Consuming the RDA for Protein.” Clinical Nutrition (Edinburgh, Scotland), U.S. National Library of Medicine, Aug. 2012, www.ncbi.nlm.nih.gov/pubmed/22357161.
  2. Balage, Michèle, and Dominique Dardevet. “Long-Term Effects of Leucine Supplementation on Body Composition.” Current Opinion in Clinical Nutrition and Metabolic Care, U.S. National Library of Medicine, May 2010, www.ncbi.nlm.nih.gov/pubmed/20110810.3- Donato, Jose, et al. “Effects of Leucine Supplementation on the Body Composition and Protein Status of Rats Submitted to Food Restriction.” Nutrition (Burbank, Los Angeles County, Calif.), U.S. National Library of Medicine, May 2006, www.ncbi.nlm.nih.gov/pubmed/16600817/.
  3. Pedroso, João A B, et al. “Reviewing the Effects of L-Leucine Supplementation in the Regulation of Food Intake, Energy Balance, and Glucose Homeostasis.” Nutrients, MDPI, 22 May 2015, www.ncbi.nlm.nih.gov/pmc/articles/PMC4446786/.
  4. Kalogeropoulou, Dionysia, et al. “Leucine, When Ingested with Glucose, Synergistically Stimulates Insulin Secretion and Lowers Blood Glucose.” Metabolism: Clinical and Experimental, U.S. National Library of Medicine, Dec. 2008, www.ncbi.nlm.nih.gov/pubmed/19013300.
  5. Liu, Hui, et al. “Leucine Facilitates the Insulin-Stimulated Glucose Uptake and Insulin Signaling in Skeletal Muscle Cells: Involving mTORC1 and mTORC2.” Amino Acids, U.S. National Library of Medicine, Aug. 2014, www.ncbi.nlm.nih.gov/pubmed/24806638.
  6. Layman, Donald K. “Role of Leucine in Protein Metabolism during Exercise and Recovery.” Canadian Journal of Applied Physiology = Revue Canadienne De Physiologie Appliquee, U.S. National Library of Medicine, Dec. 2002, www.ncbi.nlm.nih.gov/pubmed/12501002.


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