Voimailuguru Jeff Everson, Ph.D., joka toimi aiemmin Muscle & Fitness-lehden päätoimittajana, pyysi minua muutama kuukausi takaperin raapustamaan prodehydroartikkelin hänen nykyiseen lehteensä (Planet Muscle). Alla artikkelin editoimaton versio.
The Great Protein Hydrolysate Controversy
Proteins and amino acids are an important part of an diet, and as such, have been the subject of a great deal of discussion and controversy, especially in the gym rat community. More than 15 years ago some bodybuilding magazines suggested that protein hydrolysates providing mainly di- and tripeptides are superior to intact (whole) proteins and free amino acids in terms of skeletal muscle protein anabolism. This proposition was apparently based on early studies suggesting that protein hydrolysates were more effectivelty utilized in rats than intact proteins or free amino acids (e.g., Poullain et al. 1989). Obviously, rats are not small versions of gym rats, so sports nutrition experts remained highly skeptical. Nevertheless, some major sports supplement manufactures, especially TWINLAB, included protein hydrolysates in many of their products. More recently, protein hydrolysate-containing post-exercise formulations have gained some popularity (Manninen 2006).
This article will examine the latest protein hydrolysate studies conducted in healthy humans. Some old studies are also discussed to put the more recent data in some sort of perpective. Data will be analyzed from the gym rat`s perspective, so the potential benefists of protein hydrolysates in type II diabetics, etc. will not be discussed.
Recent Studies
A recent study by Farnfield and co-workers (2008), published in the International Journal of Food Science and Nutrition, examined the blood amino acid responses to intact whey protein isolate and hydrolyzed whey protein isolate. The authors reported, quite suprisingly, that intact whey protein results in a rapid absorption of amino acids into the blood compared with the hydrolyzed whey protein. Unfortunately, the authors did not provide any information on whey protein hydrolysate used in this study, other than that it was produced by Dairy Farmers, a company which does not appear to be a large-scale producer of protein hydrolysates. While the Farnfield study certainly provides some valuable data, Im not sure if it contributes much on the protein hydrolysate controversy.
On August 5 of 2008, a highly sophisticated study by Power and colleagues (2008) was published in Amino Acids. Like in the Farnfield study, protein supplements were ingested on empty stomach after an overnight fast. Neverthless, the Power study provides some interesting data for serious gym rats. Importantly, the researchers used a decent whey protein hydrolysate, so lets examine the details of their study:
- Sixteen healthy guys ingested a 500 mL solution containing either 45 grams of intack whey protein or whey protein hydrolysate.
- Somewhat suprisingly, the estimated rate of gastric (stomach) empting was not significantly altered by hydrolysis of the protein. This may have something to do with the fact that protein drinks were ingested on empty stomach after an overnight fast.
- Maximum blood insulin concentration was 28 percent greater following ingestion of the whey protein hydroysate compared to the intact whey protein, leading to a 43 percent increase in the area under curve of insulin for the whey protein hydrolysate.
- Of the amino acids with known insulin-boosting properties, only phenylalanine demonstrated a significantly greater maximal concentration and increase (+22 percent) in area under curve following ingestion of the whey protein hydrolysate, so its unclear why the protein hydrolysates have stronger insulin-boosting effects than the intact proteins.
Now, the greater insulin reponse seems to provide some indirect evidence that whey protein hydrolysate is more anabolic than intact whey protein. However, this was not examined in the Power study. Blood amino acid responses were rather similar in both groups, so should we conclude that protein hydrolysates are not absorbed more rapidly than intact proteins? I dont think so.
Firstly, the protein supplements were ingested on an empty stomach after an overnight fast, which may nullify any difference. Secondly, when it comes to the absorption kinetics, all protein hydrolysates are certainly not created equal. Each protein hydrolysate is a complex mixture of peptides of different chain length together with free amino acids, which can be defined by a global value known as degree of hydrolysis (DH), which is the fraction of peptide bonds that have been cleaved in the starter protein (Grimble 2000). However, even the exact information on DH cannot not tell us the whole story, as two protein hydrolysates made by different methods may have a similar degree of hydrolysis even though their absorption kinetics are likely quite different.
In my view, the well-controlled studies by Grimble and colleagues clearly demonstrated that protein hydrolysates containing mostly di- and tripeptides are more rapidly absorbed than those based on longer peptides (Grimble et al. 1987; Raimundo et al. 1988; Grimble et al. 1994). In their studies, protein hydrolysates produced from various sources (whey, egg, and casein) were used and the contents of di- and tripeptides were carefully analyzed.
As far as the utilization of protein hydrolysates is concerned, the study by Moriarty and colleagues (1985) is frequently cited, concluding that the molecular form of protein elicits no difference in nitrogen balance in healty humans. This was hardly surprising as the basis of the question relates to the relative rapidity of uptake of short peptides and amino acids, and in the Moriarty study this was not an issue because feeding batterns were essentially unconstrained. Under conditions of rapid intestinal (gut) infusion, amino acids from protein hydrolysates certainly appear in the portal circulation faster (Monchi and Rèrat 1993). Interestingly, Monchi and Rèrat (1993) reported that milk protein hydrolysate led to a doubling of net protein utilization compared with intact milk protein, but their study was conducted under the highly artificial situation of continuous gut infusion of a protein-free diet, with daily stomach gavage of the protein source as two boluses. In addition, Monchi and Rérat (1993) observed that blood amino acid and insulin concentrations were markedly increased. Indeed, the insulin-boosting potential of protein hydrolysates is well documented (Manninen 2006). In healthy volunteers receiving labeled casein, either intact or hydrolyzed into short peptides, protein synthesis (i.e., anabolism) over the period of study was greater with the hydrolysate (Collin-Vidal et al. 1994), presumably because it was more rapidly absorbed.
Bottom Line
While it is well-established that extensively hydrolyzed proteins containing mostly di- and tripeptides are absorbed rapidly and have strong insulin-boosting properties, more research is clearly needed concerning the utilization of these fast-acting protein hydrolysates versus intack proteins in healthy humans. In my view, future studies should carefully analyze the di- and tripeptide contents of products used. The proportion of di- and tripeptides appears to determine absorption kinetics, and in turn, it is the kinetics of the absorption (rather than the net absorption of amino acids) that determines the greater nutritional value of the protein hydrolysates.
References
Collin-Vidal C, Cayol M, Obled C, Ziegler F, Bommelaer G, Beaufrere F. 1994. Leucine kinetics are different during feeding with whole protein or oligopeptides. Am J Physiol 267:E907-14.
Farnfield MM, Trenerry C, Carey KA, Cameron-Smith D. 2008. Plasma amino acid response after ingestion of different whey protein fractions. Int J Food Sci Nutr 8:1-11.
Grimble GK, Rees RG, Keohane PP, Cartwright T, Desreumaux M, Silk DB. 1987. Effect of peptide chain length on absorption of egg protein hydrolysates in the normal human jejunum. Gastroenterology 92:136-42.
Grimble GK, Guilera Sarda M, Sesay HF. 1994. The influence of whey hydrolysate peptide chain length on nitrogen and carbohydrate absorption in the perfused human jejunum. Clin Nutr 13:46.
Grimble GK. 2000. Mechanisms of peptide and amino acid transport and their regulation. In: Furst P, Young V, eds. Proteins, Peptides and Amino Acids in Enteral Nutrition. Basel: Karger and Nestec, pp. 63–88.
Manninen AH. 2006. Hyperinsulinaemia, hyperaminoacidaemia and post-exercise muscle anabolism: the search for the optimal recovery drink. Br J Sports Med 40:900-5.
Monchi M, Rérat AA. 1993. 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 17:355-63.
Moriarty K,Hegarty J, Fairclough P, Kelly M, Clark M, Dawson A. 1985. Relative nutritional value of whole protein, hydrolysed protein and free amino acids in man. Gut 26:694-9.
Poullain MG et al. 1989. Effect of whey proteins, their oligopeptide hydrolysates and free amino acid mixtures on growth and nitrogen retention in fed and starved rats. JPEN J Parenter Enteral Nutr 13:382-6.
Power O et al. 2008. Human insulinotropic response to oral ingestion of native and hydrolysed whey protein.
Amino Acids. Aug 5. [Epub ahead of print].
Raimundo AH, Grimble GK, Rees RG, Hunjan MK, Silk DBA. 1988. The influence of fat and carbohydrate on absorption of partial enzymatic hydrolysates of casein in normal human jejenum. Gastroenterology 94:A988.
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