International Dairy Journal 16 (2006) 984–991 Physical performance of exercising young rats fed hydrolysed whey protein at a sub-optimal level Fernanda Motta Veiga Pimenta, Marı´a Ine´s Abecia-Soria, Fla´via Auler, Jaime Amaya-Farfan Food and Nutrition Department, School of Food Engineering and NEPA (Centre for Food Security Studies) of the State University of Campinas, Campinas, SP, Brazil Received 20 April 2005; accepted 5 December 2005 Abstract Exhaustion time, serum lactate, serum glucose, albumin and total proteins were determined in exercising young rats as means to assess the physiological effect of consuming a diet based on partly hydrolysed milk whey protein in comparison to the intact protein, fed at a sub-optimal protein level. A medium degree-of-hydrolysis (DH) whey protein hydrolysate (H), fed at 12% protein, have been examined. The rats were grouped according to the level of activity for sedentary (S), trained (T) and exercised to exhaustion (E) and to the type of protein in the diet: whey-protein isolate (I) or its partial hydrolysate (H). After feeding the diets under sedentary conditions for 2 weeks, the animals underwent physical training on the treadmill for 8 days, followed by an exhaustion test. Time to exhaustion and blood lactate were recorded immediately after exhaustion. Serum glucose, albumin and total proteins, and gastrocnemius protein were determined at 48 h post-exhaustion. The animals consuming the hydrolysed protein endured longer times of activity, in comparison to those consuming the isolate (156718 vs. 60713 min). Blood lactate was significantly (Po0:0001) lower in all of the hydrolysate-fed groups as compared to the rats fed the whole protein. Analogously, serum albumin levels were higher in all H groups, as compared to the I groups (Po0:001), while the levels of total serum protein were significantly higher for the trained and exhausted groups (Po0:0025). No differences in muscle protein content and glycemic levels for any of the groups were observed. It can be concluded that a dietary protein, fed at a sub- optimal level for growth in the form of a hydrolysate with medium DH may result in augmented physical performance of the exercising rat, while no adverse effects are observable. Alternatively, these observations suggest that consumption of a protein in the hydrolysed form may increase its efficiency in terms of physical performance. r 2006 Elsevier Ltd. All rights reserved. Keywords: Whey; Protein hydrolysates; Physical activity; Rat diet; Dietary protein; Bioactive peptides 1. Introduction Carbohydrates and fats are the main sources of energy at rest and during extended physical activity. Labile body proteins, however, are used as a secondary energy source but may become important during prolonged activity or starvation, when endogenous protein degradation ensues and amino acids can readily enter the deamination and energy production biochemical pathways. Intake of pro- tein-based food supplements continues to be an extensive practice among athletes seeking to enhance their muscle- building metabolism. Although a variety of proteins and amino-acid blends are of popular use without sufficient scientific evidence, special importance has been given to milk or cheese whey proteins, due to their availability and special functional properties (Ha & Zemel, 2003). It is known that besides their high supply of amino acids indispensable for growth and muscle composition (Ha & Zemel, 2003), milk whey proteins contribute with such additional health benefits as enhanced immune response, anti-oxidant activity and protection against certain types of cancer (Bounous, Batist, & Gold, 1991). This particular group of proteins is believed to contain amino-acid sequences that promote the rapid production of antibodies, thereby regulating the immune system (Bounous & Gold, ARTICLE IN PRESS www.elsevier.com/locate/idairyj 0958-6946/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.idairyj.2005.12.006 Corresponding author. Tel.: +55 19 3788 4075; fax: +55 19 3788 4060. E-mail address: jaf@fea.unicamp.br (J. Amaya-Farfan).