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Post-Meal Nitrogen Utilization and Misinterpretation of Data |
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Written by Anssi Manninen, MHS
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Tuesday, 28 November 2006 |
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A recent study by Dr. Magali Lacroix and colleagues compared the post-meal utilization of nitrogen (ie., protein anabolism) from three different proteins, namely micellar casein ("slow protein"), milk soluble protein isolate ("fast protein") and total milk protein (another "slow protein"). Their data suggested that a slow protein induces better post-meal nitrogen utilization than did a fast protein. According to the Lacroix et al., "This result, together with the hypoaminoacidemia [a low level of Amino Acids in the blood] observed 4 h after the ingestion of [milk soluble protein isolate], strongly suggests that a too-rapid dietary [amino acid] delivery cannot support the anabolic requirement throughout the postprandial period."
This is an misleading statement, as adult humans rarely, if ever, consume their dietary protein from one source only. Both fast and slow proteins have their advantages. For example, fast-acting protein hydrolysates may offer some advantages immediately post-exercise.2 In addition, frequent ingestion of fast proteins may optimize muscle protein anabolism. Dr. Paul Cribb and co-workers examined the effects of supplementation with hydrolyzed whey protein and casein on muscle strength and body composition during a 10 week, supervised resistance training program.3 The results indicated that the whey hydrolysate group achieved a significantly greater gain in lean body mass than the casein group (5.0 versus 0.8 kilograms). The whey hydrolysate group also achieved significantly greater improvements in muscle strength compared to the casein group in each assessment of strength. When the strength changes were expressed relative to body weight, the whey group still achieved significantly greater improvements in strength compared to the casein group.
The superiority of whey protein hydrolysate may have something to do with its strong insulinotopic effects2 and its rapid absorption and uptake.2 A surge of Amino Acids are rapidly transported to muscle tissue where they may help trigger muscle protein synthesis at a accelerated rate. On the other hand, slow-acting proteins may be better in minimizing muscle protein catabolism during prolonged periods between eating (e.g., pre-bed).
References
- 1. Lacroix M, Bos C, Leonil J, Airinei G, Luengo C, Dare S, Benamouzig R, Fouillet H, Fauquant J, Tome D, Gaudichon C. Compared with casein or total milk protein, digestion of milk soluble proteins is too rapid to sustain the anabolic postprandial amino acid requirement. Am J Clin Nutr 2006;84:1070-1079.
- 2. Manninen AH. Hyperinsulinaemia, hyperaminoacidaemia and post-exercise muscle anabolism: the search for the optimal recovery drink. Br J Sports Med. 2006;40:900-905.
- 3. Cribb PJ, Williams AD, Carey MF, Hayes A. The effect of whey isolate and resistance training on strenght, body composition and plasma glutamine. Int J Sports Nutr Exerc Metab 2006;16:494-509.
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Research and Review 