UACES Facebook Leucine serves an important role for health, but needs to eaten as part of a complete protein
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Leucine serves an important role for health, but needs to eaten as part of a complete protein

By Dave Edmark
U of A System Division of Agriculture

Fast facts:

  • Leucine is an essential amino acid that the body doesn’t make
  • It helps prevent protein breakdown and muscle loss
  • Leucine supplements separate from diet aren’t as effective 

(718 words)

FAYETTEVILLE, Ark. – Bodybuilding enthusiasts sometimes seek out leucine as a supplement for making their muscles bigger. The general public is less aware of its usefulness as a functional ingredient in protein that provides health benefits.

Jamie Baum, Division of Agriculture assistant professor of nutrition in the Department of Food Science. (Image courtesy Dave Edmark.) Credit mandatory.

“Leucine is one of the 20 amino acids. It’s an essential amino acid, so that means your body can’t make it,” said Jamie Baum, an assistant professor of nutrition in the University of Arkansas System Division of Agriculture Department of Food Science. As one of three branched chain amino acids, it’s highly concentrated in animal sources of protein but much less concentrated in plant sources of protein. Chicken, beef, egg, pork, fish and dairy products are proteins with high leucine levels.

Baum noted that leucine is helpful for muscle building, but muscles still need exercise to grow stronger and larger. Leucine supplements and protein shakes are popular with bodybuilders because leucine activates the mechanisms in the body that turn on protein synthesis. 

Leucine is especially useful in preventing protein breakdown and muscle loss. “That’s really important because as we age, all of us start to lose muscle mass and that can lead to frailty and loss of independence,” Baum said. “Adults over age 65 who eat high quantities of essential amino acids or protein in the morning have an increased protein synthesis rate, which is important to keep muscles building versus breaking down.”

Baum’s research shows that to be effective, leucine should be consumed as part of a protein-based diet rather than simply taken as supplement in capsules. Studies on rats that consumed a 40 percent protein diet containing leucine recorded beneficial effects, but different results occurred when leucine was simply dropped into the diet as a supplement without being part of a complete protein. In that situation, the rats’ fat mass increased and muscle gain decreased.

“When you just dump leucine on top of a diet (without protein foods), it’s missing some of the other amino acids,” Baum said. “It starts competing with other nutrients, such as fats, in your body for breakdown.”

Leucine, whether consumed through a protein diet or supplements, works best under conditions of metabolic stress, Baum said. Metabolic stress includes conditions that are common occurrences. Aging is one such stress because people’s metabolism changes with age. Obesity is another example of a body under stress, as is diabetes. Even ordinary human growth and development, as the body is growing constantly, is a form of metabolic stress. So is weight loss because calorie deficits can create metabolic stress.

“So that’s when protein or amino acids seems to work best,” Baum said. “Usually, protein or leucine supplementation in those kinds of situations show a positive effect. If you just have a healthy, young 25-year-old and they’re just supplementing with leucine without exercise, my guess is that you won’t really see an effect on muscle mass.”

Baum warned that, according to animal studies, leucine may help reduce weight gain among those who already are overweight, but it’s not likely to prevent weight gain among those are aren’t overweight. However, this is yet to be confirmed with human studies.  Tests on laboratory rats showed that a leucine supplementation administered to overweight rats resulted in a delayed or reduced weight gain compared to those who didn’t get the supplementation. Baum’s research team then wanted to see if this treatment of overweight rats could be converted to prevention. Her group gave leucine to rats on a high-fat diet that weren’t overweight, but that didn’t keep them from gaining weight.

Leucine is best consumed in the morning to maximize its benefits. Research on protein timing has shown that breakfast lives up to its reputation as the most important meal of the day.

“If you don’t get the right amount of protein at breakfast, you won’t get the benefits later in the day,” Baum said. “An animal source of protein with a high leucine concentration and eating it regularly throughout the day is important. In America we mostly eat our protein at night and that doesn’t seem to have the same benefit as equally distributing it.”

Despite the nutritional benefits from leucine and protein, the combination doesn’t make up the entire picture, Baum warned. “High quality protein is part of a healthy diet with healthy benefits, but it’s not the magic bullet people are looking for.”



The University of Arkansas System Division of Agriculture offers all its Extension and Research programs and services without regard to race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer. 


Media Contact: Mary Hightower
Dir. of Communication Services
U of A Division of Agriculture
Cooperative Extension Service
(501) 671-2126

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