Researchers at the University of Illinois at Urbana-Champaign have identified a protein molecule that stimulates muscle-building in humans to a substantial degree, paving the way for future supplementation with the wondrous molecule. Dileucine, a two-molecule version of the single amino acid leucine, enhances the metabolic processes that cause muscle-building by 42% more than leucine.

Leucine is one of three branched-chain amino acids, which have long been used by bodybuilders for their muscle-enhancing benefits. Vince Gironda, in particular, was an early advocate of taking them regularly to keep the body in a positive nitrogen balance.

As well as acting as a building block for proteins, leucine also acts as a signalling molecule that triggers muscle-building processes in cells, explains Professor Nicholas Burd, who led the new research.

New Research on Dileucine

Previous studies had focused on the digestion of amino acids and had already showed that di-peptides (molecules made up of two amino acids) are more readily absorbed than single-molecule amino acids.

“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,” Burd continues.

“And no studies have examined its effects on acute muscle-building and breakdown.”

Dileucine and leucine
Dileucine and leucine molecules

For the new study, the 10 participants (all young males) first fasted for 12-hours and then were infused with stable isotopes, chemical probes that allow researchers to track the process of muscle protein synthesis and breakdown in their muscles. Biopsies of muscle tissue were taken from the upper leg, before the administration of the amino acids under study.

The participants were then given either 2 grams of leucine or 2 grams of dileucine.

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. 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 researchers then investigated whether dileucine was having any effect on muscle-building in the participants who took it.

“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.”

Results from the study

The researchers discovered that those who consumed dileucine had 42% more synthesis of new muscle proteins than those who ingested leucine instead. This is a significant boost that compares favourably with the protein-building boost that comes from exercise.

“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 (see the table below). We’ve already written an article on just how unfavourably plant proteins compare to animal proteins.

Comparison of dileucine content of various forms of protein

While Burd told Science Daily that he does not think people should start ingesting large amounts of animal protein or taking dileucine supplements to enhance their muscle metabolism, start-up Ingenious Ingredients is already commercializing the molecule as a muscle-builder.

The company has already obtained a US patent for using the molecule, and additional American and international patents are now pending.

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While the primary market for dileucine supplements might appear to be young men interested in building muscle, Ingenious Ingredients plants to target other demographics that might be in need of a muscle-building boost, such as the elderly and ‘populations that have an overall negative nitrogen balance, meaning they are losing muscle mass, eg. during calorie restriction, during immobilization or hospitalization (muscle disuse atrophy),” according to Ingenious founder Dr Ralf Jaeger.

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