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What is it?

Leucine is an essential amino acid. You've probably heard that phrase before, here's what it means. There are at least eight amino acids that our bodies have to get from outside sources. They're called "essential" because we can't make them, and we can't live without them.

Protein is made up of amino acids. Our bodies need protein and the amino acids it's made from to build muscle and survive.

That means whenever we eat foods with all the essential amino acids in them, we’re getting a little leucine. We also get some leucine in any protein supplement that says it includes "all the essential amino acids."

Does it occur naturally in the body?


What are the claims?

Supplement companies are claiming that by adding extra leucine to their protein mixes, it makes them more effective muscle builders.

Does it work?

The studies being promoted by supplement companies usually had two groups of people. One took a protein supplement with leucine; the other didn't take anything at all. At the end of the study, the group taking leucine and protein saw greater muscle growth.

Unfortunately, those studies don't tell me anything about leucine. You see, there are hundreds of studies through the years that show taking protein after a workout will stimulate muscle growth. It's an established fact. If you compare one group of people who take nothing, to another group that takes protein and leucine, the people who take the protein are always going to do better.

What I needed are studies where there were two groups of people. One that got protein only, and the other that got protein with leucine. Over the last few years, a couple of them have taken place. Here's what they found.

A University of Texas study done in 2009 declared that "whey protein plus leucine in healthy young volunteers results in an anabolic response in muscle that is NOT GREATER [emphasis ours] than the previously reported response to whey protein alone."

Whey protein - good, whey protein with leucine - no added benefit.

Maastricht University in the Netherlands did a similar study in 2008, and they concluded that, "Co-ingestion of leucine with carbohydrate and protein following physical activity does not further elevate muscle protein fractional synthetic rate in elderly men when ample protein is ingested."

They discovered the same thing the University of Texas did. Protein alone is good. Protein with added leucine provides no additional benefit. If you're spending more for the combo, you're wasting your money.

Having said that, there are at least three situations where clinical trials suggest added leucine may be of benefit.

  • If you're over the age of 65 and don't workout,
  • are just beginning to workout or
  • are experiencing muscle wasting.

Each of those conditions show a very slight improvement in muscle growth for the people taking protein with added leucine versus standard whey protein alone.

What are the dangers?

None that we've been able to find as of 7/14/2011.

The Bottom Line

Do not buy leucine supplements or leucine in protein powder unless you're over the age of 65 and don't workout, you're just beginning to workout for the first time or are experiencing muscle wasting.

Links for More Info

Centers for Disease Control and Prevention (CDC) Logo and Link
Centers for Disease Control and Prevention

United States Food and Drug Administration (FDA)

Herbs, Botanicals & Other Products - Extensive Information from the Memorial Sloan-Kettering Cancer Center

National Center for Complementary and Integrative Health - Overviews on Herbal Treatments and Supplements

National Institutes of Health

National Institutes of Health - Office of Dietary Supplements
National Institutes of Health - Office of Dietary Supplements

Operation Supplement Safety
Operation Supplement Safety

United States Department of Agriculture (USDA) Logo and Link
United States Department of Agriculture

WebMD Logo and Link
WebMD - Helping you make better decisions for life.

We at WeBeFit DO NOT recommend ANY supplements to ANY of our clients. ONLY a licensed Nutritionist or Medical Doctor can make those recommendations based on your individual needs.

This is being provided for INFORMATIONAL and EDUCATIONAL purposes only.

CAUTION: These supplements have not been evaluated by the Food and Drug Administration (FDA) for safety, effectiveness or purity. There may be unknown risks associated with taking any supplements. There are no regulated manufacturing standards for companies that make supplements. There have been instances where herbal or health supplements have been sold that were contaminated with toxic substances. If you should choose to purchase herbal or health supplements, please only purchase them from a reliable source to minimize the risk of contamination.

If you should decide to use ANY supplement, ALWAYS consult your doctor or Nutritionist first.