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Nowadays, almost every major sports nutrition company has a top tier protein supplement that contains whey protein hydrolysate as the major ingredient. This is because it is generally accepted that whey protein hydrolysate is the best protein to augment the anabolic stimulus response to resistance training1. But up until a short while ago, scientists were still at odds as to what specific components of whey protein hydrolysates where responsible for this superior anabolic response. A series of recent studies by a group of Japanese researchers has been pivotal in answering these questions2-6. As it turns out, the most powerful and important anabolic component of whey protein hydrolysates is their content of branched-chain amino acid (BCAA)-containing dipeptides2.

The Science of Whey Protein Hydrolysates

Before we get into the nitty gritty of dipeptide composition of whey protein hydrolysates, let’s start by establishing what we already know about whey protein hydrolysates compared to intact whey protein. Based on the science thus far, this is what we know:

  1. Blood levels of total amino acids following whey protein hydrolysate ingestion peak earlier and higher than after ingestion of intact whey protein2.
  2. Blood levels of essential amino acids following whey protein hydrolysate ingestion peak earlier and higher compared with ingestion of intact whey protein2.
  3. Blood levels of branched-chain amino acids following whey protein hydrolysate ingestion peak earlier and higher compared with ingestion of intact whey protein2.
  4. Plasma insulin peaks higher and earlier following ingestion of whey protein hydrolysate versus intact whey protein2.

So in short, amino acids from whey protein hydrolysates get into the blood quicker and reach higher levels, while also stimulating higher insulin levels than amino acids from intact whey protein2. Pretty cool stuff really. In a nutshell, these differences in the digestion and absorption parameters of whey protein hydrolysate are also why it’s thought to provide a greater anabolic stimulus following intense weight training.

Dipeptides in Whey Hydrolysates vs Intact Whey

It was only after the publication of a pivotal study by Masashi Morifuji and his colleagues from the Food and Health R&D Laboratories at Waseda University, Japan in 2011 - that it was clear how differences in amino acid composition of whey protein hydrolysates and intact whey proteins explain their differing anabolic responses. Moreover, it was not so much the difference in amino acid composition as it was differences in the form of amino acids. As discussed in our article on hydrolysed protein, whey protein hydrolysates contain higher levels of di- and tri-peptides than intact whey. These key differences it seems result from the specific enzymes that whey protein is subjected to in order to produce its hydrolysate derivatives2.

Interestingly, the peptide-rich protein hydrolysates produced by industrial enzymes are significantly different to the products of whey protein digestion by the human gastrointestinal tract2. While it has been established for some time that whey protein hydrolysates contain higher levels of di- and tri-peptides, Morifiju and his colleagues are the first to uncover the specific di- and tri-peptides that are higher in whey protein hydrolysates. Morifuji showed that whey protein hydrolysates contain higher levels of BCAA-containing dipeptides compared to non-hydrolysed sources. More specifically, plasma concentrations of leucine-dipeptides, namely: valine-leucine and isoleucine-leucine; where dramatically higher compared to other protein sources in the study by Morifuji2.

Leucine-Containing Dipeptides Key to Anabolic Response

We know from studies as far back as the 70’s and 80’s that di- and tri-peptides are absorbed more rapidly than whole protein or free amino acids7-12 and that the main products of protein digestion in the gut lumen are not single amino acids, but rather di- and tri-peptides7, 8. Moreover, researchers have even identified and characterised the intestinal oligopeptide transporter (i.e. Pept-1) that mediates the rapid uptake of di- and tri-peptides in the small intestine13, 14. So it’s reasonable to infer that the high concentration of leucine-dipeptides in whey protein hydrolysate is the key component responsible for the rapid rise and high blood levels of leucine and BCAAs relative to whey protein. What’s more, the high blood levels of leucine achieved with whey protein hydrolysates are key to their superior anabolic properties, because of leucine’s critical role in stimulating muscle protein synthesis1.

BCAA-Peptide Content on Labels

Certain sport nutrition companies have already started to modify their labels to reflect the specific BCAA-containing dipeptide content of their whey protein hydrolysates. This trend is likely to continue with other major sports nutrition brands as developments in this area are confirmed in further studies.

Benefits of BCAA-Dipeptides

Aside from mediating the anabolic effects of whey protein hydrolysates, Morifuji and his colleagues have shown that BCAA-dipeptides have other beneficial effects, particularly in endurance exercise, where they have been shown to help with muscle glucose uptake3 and glycogen resynthesis4, 5. So watch this space as further research uncovers more nutritional benefits for BCAA-dipeptides. Don’t be surprised if products containing pure isolated specific BCAA-dipeptides start popping up all over the place.

1. West DW, Burd NA, Coffey VG, et al. Rapid aminoacidemia enhances myofibrillar protein synthesis and anabolic intramuscular signaling responses after resistance exercise. Am J Clin Nutr. 2011;94(3):795-803.
2. Morifuji M, Ishizaka M, Baba S, 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):8788-8797.
3. Morifuji M, Koga J, Kawanaka K, Higuchi M. 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.
4. Morifuji M, Kanda A, Koga J, et al. Post-exercise carbohydrate plus whey protein hydrolysates supplementation increases skeletal muscle glycogen level in rats. Amino Acids. 2010;38(4):1109-1115.
5. Morifuji M, Kanda A, Koga J, et al. Preexercise ingestion of carbohydrate plus whey protein hydrolysates attenuates skeletal muscle glycogen depletion during exercise in rats. Nutrition. 2011;27(7-8):833-837.
6. Aoi W, Takanami Y, Kawai Y, et al. Dietary whey hydrolysate with exercise alters the plasma protein profile: a comprehensive protein analysis. Nutrition. 2011;27(6):687-692.
7. Adibi SA. Intestinal transport of dipeptides in man: relative importance of hydrolysis and intact absorption. J Clin Invest. 1971;50(11):2266-2275.
8. Adibi SA, Morse EL, Masilamani SS, Amin PM. Evidence for two different modes of tripeptide disappearance in human intestine. Uptake by peptide carrier systems and hydrolysis by peptide hydrolases. J Clin Invest. 1975;56(6):1355–1363.
9. Grimble GK, Keohane PP, Higgins BE, et al. Effect of peptide chain length on amino acid and nitrogen absorption from two lactalbumin hydrolysates in the normal human jejunum. Clin Sci (Lond). 1986;71(1):65-69.
10. Grimble GK, Rees RG, Keohane PP, et al. Effect of peptide chain length on absorption of egg protein hydrolysates in the normal human jejunum. Gastroenterology. 1987;92(1):136-142.
11. Rérat A, Simoes-Nuñes C, Mendy F, et al. Splanchnic fluxes of amino acids after duodenal infusion of carbohydrate solutions containing free amino acids or oligopeptides in the non-anaesthetized pig. Br J Nutr. 1992;68(1):111-38.
12. Monchi M, Rérat AA. Comparison of net protein utilization of milk protein mild enzymatic hydrolysates and free amino acid mixtures with a close pattern in the rat. J Parenter Enteral Nutr. 1993;17(4):355-363.
13. Fei YJ, Kanai Y, Nussberger S, et al. Expression cloning of a mammalian proton-coupled oligopeptide transporter. Nature. 1994;368(6471):563-566.
14. Fei YJ, Sugawara M, Liu JC, et al. cDNA structure, genomic organization, and promoter analysis of the mouse intestinal peptide transporter PEPT1. Biochim Biophys Acta. 2000;1492(1):145-154.

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