Dileucine stimulates muscle building more effectively than free leucine, study finds

10 Aug 2021 --- Dileucine, a dipeptide consisting of two leucine molecules, boosts the metabolic processes that drives muscle growth 42 percent more than free leucine does, according to a randomized control study.

The double-blind study, conducted by the University of Illinois, US, consisted of ten healthy young men. Researchers compared how consuming the single amino acid leucine or its two-molecule equivalent, dileucine, influenced muscle-building and breakdown.

“Our findings provide insight into the mechanisms of the anabolic functions of protein foods,” Kevin Paulussen, Department of Kinesiology and Community Health at the University of Illinois tells NutritionInsight.

“One of the findings of our study was that known high-quality protein foods, as dictated by their capacity to stimulate muscle protein synthesis, are also relatively high in dileucine.”

To our knowledge, this is the first study investigating the effects of dileucine ingestion on human muscle protein metabolism, he notes.

“We have yet to identify a mechanism by which dileucine exerts its anabolic action. This study provides a first step toward understanding the function of dileucine as a nutritional compound.”Dileucine ingestion is more effective than leucine in stimulating muscle protein turnover in young males.

The researchers also showed that animal-based proteins are the best source of dileucine in the diet.

However, Nicholas Burd, kinesiology and community health professor at the University of Illinois, does not think people should start ingesting large amounts of animal protein or taking dileucine supplements to enhance muscle metabolism.

The study is 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.”

Dipeptides more effective than amino acids?
The researchers were aware, from previous research, that dipeptides may get absorbed more rapidly than single amino acids by the small intestine, Paulussen notes.

“Based on past efforts showing that dileucine may appear in the blood faster than leucine alone, we hypothesized that dileucine would have greater potential for stimulating muscle protein synthesis than leucine.”

Digestion breaks the chemical bonds between the amino acids that make up proteins, resulting in a collection 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, notes Burd.

“We looked at pathways that signal the muscle-building process, including protein breakdown as part of the remodeling process. We found no difference in protein breakdown between the leucine alone and the dileucine condition,” says Burd.

“But on the protein synthesis side, we saw that dileucine turns up the muscle-building process more than leucine does. This is just a first attempt to understand how these types of peptides are playing a role in human physiology.”

Muscle building and breakdown 
Few studies have examined whether dileucine in the diet makes it into the blood as a dipeptide or broken down into two leucine molecules, Burd notes.

“No studies have examined its effects on acute muscle building and breakdown.”Branched-chain amino acids drive skeletal muscle protein synthesis.

Burd’s laboratory is one of a few research facilities set up specifically to study muscle protein metabolism in human participants.

For the new study, participants came to the lab after a 12-hour fast. They 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 g leucine or 2 g dileucine, and we studied their muscle-remodeling response for three hours,” says Burd.

Three more muscle biopsies were taken at 30, 60 and 180 minutes after participants ingested the leucine or dileucine. The study results were published in the Journal of Applied Physiology.

BCAAs’ function
Leucine, isoleucine and valine all are branched-chain amino acids (BCAAs) known for their muscle-enhancing benefits.

“The BCAAs are involved in triggering skeletal muscle protein synthesis. In particular, the BCAA leucine is heavily researched as a signaling molecule for the stimulation of muscle protein synthesis,” says Paulussen.

“Leucine is interesting, as it seems to play a key role in dictating the anabolic potency of a protein source. Because of this, leucine as a supplement provides the opportunity to fortify protein formulations in an attempt to increase its anabolic potency.”

Industry players are interested in muscle development. In this space, a study conducted at Waseda University in Japan found that consuming protein for breakfast is more effective for muscle growth than consuming it during dinner.

By Nicole Kerr