Int J Sports Med 2015; 36(08): 636-646
DOI: 10.1055/s-0034-1398647
Physiology & Biochemistry
© Georg Thieme Verlag KG Stuttgart · New York

Whey or Casein Hydrolysate with Carbohydrate for Metabolism and Performance in Cycling

T. Oosthuyse
1   Exercise Laboratory, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Medical School, Johannesburg, South Africa
,
M. Carstens
1   Exercise Laboratory, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Medical School, Johannesburg, South Africa
,
A. M. E. Millen
1   Exercise Laboratory, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Medical School, Johannesburg, South Africa
› Author Affiliations
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Publication History



accepted after revision 04 November 2014

Publication Date:
05 May 2015 (online)

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Abstract

The protein type most suitable for ingestion during endurance exercise is undefined. This study compared co-ingestion of either 15 g/h whey or casein hydrolysate with 63 g/h fructose: maltodextrin (0.8:1) on exogenous carbohydrate oxidation, exercise metabolism and performance. 2 h postprandial, 8 male cyclists ingested either: carbohydrate-only, carbohydrate-whey hydrolysate, carbohydrate-casein hydrolysate or placebo-water in a crossover, double-blind design during 2 h of exercise at 60%W max followed by a 16-km time trial. Data were evaluated by magnitude-based inferential statistics. Exogenous carbohydrate oxidation, measured from 13CO2 breath enrichment, was not substantially influenced by co-ingestion of either protein hydrolysate. However, only co-ingestion of carbohydrate-casein hydrolysate substantially decreased (98% very likely decrease) total carbohydrate oxidation (mean±SD, 242±44; 258±47; 277±33 g for carbohydrate-casein, carbohydrate-whey and carbohydrate-only, respectively) and substantially increased (93% likely increase) total fat oxidation (92±14; 83±27; 73±19 g) compared with carbohydrate-only. Furthermore, only carbohydrate-casein hydrolysate ingestion resulted in a faster time trial (−3.6%; 90% CI: ±3.2%) compared with placebo-water (95% likely benefit). However, neither protein hydrolysate enhanced time trial performance when compared with carbohydrate-only. Under the conditions of this study, ingesting carbohydrate-casein, but not carbohydrate-whey hydrolysate, favourably alters metabolism during prolonged moderate-strenuous cycling without substantially altering cycling performance compared with carbohydrate-only.