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Leucine peptides

Leucine peptide is a general term used to describe certain leucine-containing di- and tripeptides. Leucine peptides are appearing in more and more different sports supplements, ranging from pre-workout products to post-workout products. Contrary to what you might think, leucine peptides are more than just a gimmick and their effects are supported by a solid study base. Leucine peptides have been shown to have unique benefits for both endurance and strength development.

What are leucine peptides?

Although the term leucine peptides can encompass a very wide range of di- and tripeptides, there are some very specific leucine peptides that have been shown to have unique benefits. In theory, a leucine peptide can consist of a leucine molecule and any other amino acid, but the specific leucine peptides with proven benefits are the peptides in which leucine is bound to a branched-chain amino acid. Japanese scientists have identified the following key leucine peptides (1):

  • Valine-leucine
  • isoleucine-leucine
  • leucine-leucine
  • leucine-valine
  • Leucine-isoleucine

Absorption of leucine peptides

One of the unique properties of leucine peptides is the way in which they are absorbed after oral ingestion. Leucine peptides such as those mentioned above have been shown to be absorbed faster than free amino acids or complete proteins such as whey protein and soy protein (2). When consumed as part of a whey protein hydrolysate, leucine peptides tend to reach their highest concentration in the bloodstream after 30 minutes. Very small amounts of leucine peptides are also found in the blood after consuming whey protein or soy protein, but the blood levels reached are much lower than the levels that can be measured after consuming a whey protein hydrolysate (2). The body has a greater capacity for absorbing di- and tripeptides than free amino acids. This is believed to be mainly due to the presence of a specific peptide transporter called Pept 1. Pept 1 is located on the membrane of the intestinal epithelium and mediates the uptake of di- and tripeptides from the intestinal lumen into the enterocytes (3).

Benefits of leucine peptides

Japanese scientists at Waseda University are among the leading researchers who have discovered specific health and performance benefits of leucine peptides. They have found that leucine peptides have performance benefits for both endurance athletes and strength athletes.

Benefits of leucine peptides for endurance

Some specific benefits for endurance athletes include the ability to improve glycogen storage and glycogen utilization during exercise (4, 5). Naturally occurring leucine peptides from whey protein hydrolysate have been shown to increase glycogen synthesis when taken after exercise (5). And when taken on a daily basis over several weeks, whey protein hydrolysate containing leucine peptides can improve the ability of muscles to store glycogen (4, 6), with this effect being significantly stronger compared to whey protein and branched-chain amino acids. It has also been shown that leucine peptides, when taken before exercise, reduce glucose utilization during exercise and thus increase endurance (4). Studies conducted in mice have also shown that low molecular weight peptides (such as leucine peptides) from whey protein hydrolysate increased endurance in swimming tests by lowering lactate levels and increasing glucose and fatty acid concentrations during exercise (6).

Benefits of leucine peptides for muscle building

When it comes to strength training and muscle hypertrophy, the research is not quite as extensive. However, there are some studies that show that leucine peptides from whey protein hydrolysate lead to greater muscle protein synthesis (7, 8). The key premise of leucine peptides is that their unique di- and tripeptide form have superior effects compared to free amino acids or whole proteins.

An intelligently designed study proving this assumption showed that a whey protein hydrolysate containing leucine peptides resulted in a greater stimulation of muscle protein synthesis compared to a mixture of free amino acids (7). This was the case despite the fact that both mixtures of amino acids resulted in similar plasma levels of amino acids (7). Thus, it appears that leucine in peptide format carries some kind of information or biological message.

Supplement forms of leucine peptides

The most widely used form of leucine peptides is a proprietary ingredient called Pepform™, which contains 46% leucine, most of which is in peptide form. In addition, highly hydrolyzed whey protein hydrolysate also contains traces of leucine peptides.

Final evaluation

Leucine peptides are one of the most exciting supplement ingredients in the field of sports nutrition research and are very promising in terms of their performance benefits. Unfortunately, they are still very expensive to produce, which has prevented their widespread use in the supplement market. However, as new research continues to be published supporting their efficacy in muscle building and improvements in endurance performance, the demand for leucine peptides should steadily increase, hopefully resulting in more cost-effective production and wider use in supplements.

References

  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.