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Leucine peptides is the general term used to define certain leucine-containing di- and tripeptides. Leucine peptides are appearing at an increasing rate in various sports supplements from pre workouts to post workouts. Rather than being something of a gimmick, leucine peptides have a solid base of research behind them and have been shown to have a range of unique benefits, both for endurance and strength development.

What Are Leucine Peptides?

While leucine peptides can encompass a very broad range of dipeptides and tripeptides, there are some very specific leucine peptides that have been shown to have unique benefits. In theory, a leucine peptide can be a leucine residue joined to any amino acid, but the specific leucine peptides with proven benefits are those that involve leucine being bound to a branched-chain amino acid. Japanese researchers1 have identified key leucine dipeptides in the form of:

  • Valine-Leucine
  • Isoleucine-Leucine
  • Leucine-Leucine
  • Leucine-Valine
  • Leucine-Isoleucine

Absorption of Leucine Peptides

One of the unique features of leucine peptides is how they are absorbed after oral ingestion. Leucine peptides such as the ones mentioned above have been shown to be absorbed more quickly than single amino acids or whole proteins such as whey or soy protein2. When ingested as part of a whey protein hydrolysate, leucine peptides tend to reach peak values in blood within 30 minutes. Very small amounts of leucine peptides are also found in blood after ingesting whole whey protein and soy protein, but the levels they reach in blood are much lower than those achieved with whey protein hydrolysate.2 The body also has a greater capacity for absorption of di- and tripeptides than single amino acids. This is thought to be due largely to the presence of a specific intestinal peptide transporter called Pept 1. Pept 1 is located on the brush border membrane of the intestinal epithelium and mediates the uptake of di- and tripeptides from the gut lumen into the enterocytes3.

Benefits of Leucine Peptides

Japanese researchers from Waseda University are among the leading researchers in the world who have uncovered the specific health and performance benefits of leucine peptides. They have discovered that leucine peptides offer performance benefits for both endurance and strength training athletes.

Benefits of Leucine Peptides for Endurance

Some of the specific benefits for endurance athletes include the ability to improve glycogen storage and use during exercise4, 5. More specifically, naturally occurring leucine peptides from whey protein hydrolysate have been shown to increase glycogen synthesis when taken post exercise compared with glucose alone5. And when used on a daily basis for several weeks, whey protein hydrolysate containing leucine peptides can improve the ability of muscles to store glycogen, when compared with whey protein or branched-chain amino acids4, 6. Moreover, when taken before exercise, leucine peptides have been shown to reduce glycogen use during exercise, thus increasing endurance4. Studies in mice have also shown that low molecular weight peptides (such as leucine peptides) from whey protein hydrolysate improve swimming endurance by decreasing lactate levels and improving concentrations of glucose and fatty acids during exercise6.

Benefits of Leucine Peptides for Muscle Gain

When it comes to strength training and muscle hypertrophy, the research is not as extensive; nonetheless, there are a couple of studies showing leucine peptides from whey protein hydrolysate lead to greater muscle protein synthesis7, 8. The key premise with leucine peptides is that their unique di- and tripeptide format is thought to confer superior effects compared with free form amino acids or whole protein. One cleverly designed study, which proved this notion showed that compared with a free form amino acid mixture identical in composition, a whey protein hydrolysate containing leucine peptides resulted in greater stimulation of muscle protein synthesis7. This was despite the fact that both mixtures of amino acids resulted in similar plasma levels of amino acids7. So it would appear that in peptide format, leucine residues carry some type of information or biological message.

Supplemental Forms of Leucine Peptides

The most common form of leucine peptides appearing in supplements is one made by Glanbia Nutritionals called PepformTM Leucine Peptide. This particular raw material contains 46% leucine, where the majority of the leucine occurs in peptide form. As stated by Glanbia, the raw material is made using advanced fractionation and separation technologies that bind free form leucine to leucine peptides isolated from fresh sweet whey. The other types of products which may contain small traces of leucine peptides are whey protein hydrolysates that carry a high degree of hydrolysis. Some examples include BNRG Proto Whey, Elemental Nutrition Peptide ProteinGaspari Aminolast, Elemental Nutrition Peptides and Maxs WPI HL.

In closing, leucine peptides are one of the most exciting prospects in sports nutrition research and hold a tremendous amount of promise for performance benefits. Unfortunately, they are still very expensive to manufacture, which has hindered their wide spread incorporation into sports supplements. Nonetheless, if new research continues to emerge supporting their efficacy for muscle development and endurance performance, demand should steadily increase –hopefully resulting in more cost-effective means of production and ultimately more widespread use in supplements.


1. Morifuji M, et al. Branched-chain amino acid-containing dipeptides, identified from whey protein hydrolysates, stimulate glucose uptake rate in L6 myotubes and isolated skeletal muscles. J Nutr Sci Vitaminol (Tokyo). 2009;55(1):81-86.
2. Morifuji M, et al. Comparison of different sources and degrees of hydrolysis of dietary protein: effect on plasma amino acids, dipeptides, and insulin responses in human subjects. J Agric Food Chem. 2010;58(15):8788-97.
3. Kanda A, et al. Post-exercise whey protein hydrolysate supplementation induces a greater increase in muscle protein synthesis than its constituent amino acid content. British Journal of Nutrition. 2013;110:981–987.
4. Adibi SA. Regulation of expression of the intestinal oligopeptide transporter (Pept-1) in health and disease. Am J Physiol Gastrointest Liver Physiol. 2003;285(5):G779–88.
5. Morifuji M, et al. Preexercise ingestion of carbohydrate plus whey protein hydrolysates attenuates skeletal muscle glycogen depletion during exercise in rats. Nutrition. 2011;27(7-8):833-7. 
6. Liu J, et al. Effect of whey protein hydrolysates with different molecular weight on fatigue induced by swimming exercise in mice. J Sci Food Agric. 2014;94(1):126-130. 
7. Morifuji M, et al. Post-exercise carbohydrate plus whey protein hydrolysates supplementation increases skeletal muscle glycogen level in rats. Amino Acids. 2010;38(4):1109-15. 
8. Tang JE, et al. Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men. J Appl Physiol. 2009;107:987–992.

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