Study identifies molecule that stimulates muscle-building in humans


Date:
August 9, 2021
Source:
University of Illinois at Urbana-Champaign, News Bureau
Summary:
In a randomized control study of 10 healthy young men, researchers
compared how consuming the single amino acid leucine or its
two-molecule equivalent, dileucine, influenced muscle-building
and breakdown. They found that dileucine boosts the metabolic
processes that drive muscle growth 42% more than free leucine does.



FULL STORY ==========================================================================
In a randomized control study of 10 healthy young men, researchers
compared how consuming the single amino acid leucine or its two-molecule equivalent, dileucine, influenced muscle-building and breakdown. They
found that dileucine boosts the metabolic processes that drive muscle
growth 42% more than free leucine does.


==========================================================================
They report their findings in the Journal of Applied Physiology.

Leucine, isoleucine and valine all are branched-chain amino acids,
famous among body builders and health enthusiasts for their purported muscle-enhancing benefits. Like other amino acids, they are the building
blocks of proteins. But leucine also acts as a signaling molecule that
triggers muscle-building pathways in cells, said University of Illinois Urbana-Champaign kinesiology and community health professor Nicholas
Burd, who led the new research with kinesiology graduate student Kevin Paulussen.

Digestion breaks the chemical bonds between the amino acids that make
up proteins, resulting in a stew of shorter molecules, including free
amino acids and dipeptides. Previous studies have suggested that the
small intestine absorbs dipeptides like dileucine more rapidly than
their single-molecule counterparts, Burd said.

"But few studies have examined whether dileucine in the diet makes it
into the blood as a dipeptide or is first broken down into two leucine molecules," he said. "And no studies have examined its effects on acute muscle-building and breakdown." Burd's laboratory is one of a small
number of research facilities set up to study muscle protein metabolism
in human participants.

For the new study, participants came to the lab after a 12-hour fast and
were infused with stable isotopes, chemical probes that allow researchers
to track the process of muscle protein synthesis and breakdown in their muscles. Then biopsies of muscle tissue were taken from the upper leg.



========================================================================== "After that, we fed them either 2 grams of leucine or 2 grams
of dileucine," Burd said. "And we studied their muscle-remodeling
response for three hours." This was a double-blind study, meaning
that the data were coded to prevent participants and researchers from
knowing who received leucine or dileucine in the initial phases of the
study. Three more muscle biopsies were taken, at 30, 60 and 180 minutes
after participants ingested the leucine or dileucine.

"We found that leucine got into the blood more quickly when participants consumed dileucine than if they had just free leucine," Burd said. "That
means that some of that dileucine is getting hydrolyzed, or cut up,
before it gets into the bloodstream. But we also saw that dileucine was
getting into the bloodstream intact." The next question was whether
dileucine had any effect on muscle-building processes, he said.

"So, we looked at pathways that signal the muscle-building process,
including protein breakdown as part of the remodeling process. And we
found no difference in protein breakdown between the leucine alone and
the dileucine condition," Burd said. "But on the protein synthesis side,
we saw that dileucine turns up the muscle-building process more than
leucine does." Those who consumed dileucine had 42% more synthesis of
new muscle proteins than those who ingested only leucine.

"To put that in perspective, exercise alone can cause a 100-150% increase
in the muscle-building response," Burd said.

The researchers also showed that animal-based proteins are the best
source of dileucine in the diet. But Burd does not think people should
start ingesting large amounts of animal protein or taking dileucine
supplements to enhance their muscle metabolism. The study is only a first
step toward understanding how the body uses dipeptides, "and focusing
on a single nutrient doesn't provide a perspective on how the overall
diet and eating pattern impacts muscle growth," he said.

"We don't yet know the mechanism by which dileucine works,"
Burd said. "This is just a first attempt to understand how
these types of peptides are playing a role in human physiology." ========================================================================== Story Source: Materials provided by University_of_Illinois_at_Urbana-Champaign,_News_Bureau.

Original written by Diana Yates. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Kevin J. M. Paulussen, Rafael A. Alamilla, Amadeo F. Salvador,
Colleen F.

McKenna, Andrew T. Askow, Hsin-Yu Fang, Zhong Li, Alexander
V. Ulanov, Scott A. Paluska, John A. Rathmacher, Ralf Ja"ger,
Martin Purpura, Nicholas A. Burd. Dileucine ingestion is more
effective than leucine in stimulating muscle protein turnover in
young males: a double blind randomized controlled trial. Journal
of Applied Physiology, 2021; DOI: 10.1152/japplphysiol.00295.2021 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210809100508.htm

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