OBJECTIVE: This study compared the effects of casein and whey protein as the source of dietary protein on the activity of lipogenic enzymes and mRNA levels in the liver and skeletal muscle of exercise-trained rats.

METHODS: Twenty-eight male Sprague-Dawley rats were randomly assigned to one of four groups (n = 7/group). Rats were assigned to sedentary or exercise-trained groups and were fed the casein or whey protein diet. Rats in the exercise groups were trained for 2 wk using a swimming exercise for 120 min/d and 6 d/wk.

RESULTS: A significant decrease in the activity of the hepatic lipogenic enzymes, glucose-6-phosphate dehydrogenase, malic enzyme, adenosine triphosphate citrate lyase, acetyl-coenzyme A carboxylase, and fatty acid synthase (FASN) was observed in rats fed whey protein compared with animals fed casein. Compared with the casein diet, the whey protein diet also lowered mRNA expression of these enzymes, except for FASN. In contrast to the findings in liver, whey protein, as compared with casein, increased skeletal muscle FASN activity and mRNA. Further, exercise training resulted in increased skeletal muscle glucose-6-phosphate dehydrogenase and FASN activity and adenosine triphosphate citrate lyase, acetyl-coenzyme A carboxylase-1, and FASN mRNA expression.

CONCLUSIONS: Exercise training or whey protein may play an important role in suppressing hepatic fatty acid synthesis, thereby decreasing accumulation of body fat and stimulating the skeletal muscle to increase energy substrate as fat during prolonged exercise.

Endocrine responses to repeated exercise have hardly been investigated and no data are available regarding the mediating influence of nutrition. On three occasions, participants ran for 90 min at 70% VO2max (R1) before a second exhaustive treadmill run at the same intensity (R2; 91.6± 17.9 min). During the intervening 4 h recovery, participants ingested either: (i) 0.8 g sucrose·kg-1·h-1 with 0.3 g·kg-1·h-1 whey protein isolate (CHO-PRO); (ii) 0.8 g sucrose·kg-1·h-1 (CHO) or; (iii) 1.1 g sucrose·kg-1·h-1 (CHO-CHO). The latter two solutions therefore matched the formerfor carbohydrate or for available energy, respectively. Serum growth hormone concentrations increased from 1.7±0.9 μg·l-1 to 16.7±7.8 μg·l-1 during R1 considered across all treatments (means±standard deviations; P≤0.01). Concentrations were similar immediately after R2 irrespective of whether CHO or CHO-CHO was ingested (19±4 μg·l-1 and 19±5μg·l-1, respectively), whereas ingestion of CHO-PRO produced an augmented response (31±4μg·l-1; P≤0.05). Growth hormone binding protein concentrations were unaffected by R1 but increased similarly across all treatments during R2 (414±202 pmol·l-1 to 577±167 pmol·l-1; P≤0.01), as was the case for plasma total testosterone (9.3±3.3 nmol·l-1 to 14.7±4.6 nmol·l-1; P≤0.01). There was an overall treatment effect for serum cortisol (P≤0.05), with no specific differences at any given time-point but lower concentrations immediately after R2 with CHO-PRO (608±133 nmol·l-1) than CHO (796±278 nmol·l-1) or CHO-CHO (838±134 nmol·l-1). Ingesting carbohydrate with added whey protein isolate during short-term recovery from 90 minutes of treadmill running increases the growth hormone response to a second exhaustive exercisebout of similar duration.

A number of different forms of protein and their analogues have been investigated for their efficacy in ameliorating exercise-induced muscle damage (EIMD) and recovery. Preliminary data regarding whey protein hydrolysate (WPH) supplementation are promising. However, its efficacy beyond acute eccentric/resistance exercise bouts or longer term training programmes are limited and all investigations have been conducted in male or mixed-sex groups. This study sought to elucidate whether the benefits of WPH previously reported can be demonstrated in females following repeated-sprint exercise. Twenty physically active females were assigned to consume 2 doses of 70 mL WPH or isoenergetic carbohydrate (CHO) for 4 days post-EIMD. Measures of muscle soreness, limb girth, flexibility, muscle function, and creatine kinase were collected before, immediately after, and 24, 48, and 72 h postexercise. Time effects were observed for all variables (p<0.05) except limb girth, which is indicative of EIMD. Flexibility improved beyond baseline measures following WPH by 72 h, but had failed to recover in the CHO group (p = 0.011). Reactive strength index was higher throughout recovery in the WPH group compared with CHO (p = 0.016). Reductions in creatine kinase were greater following WPH compared with CHO at 48 h post-EIMD (p = 0.031). The findings suggest that 4-day supplementation of WPH is beneficial for reducing symptoms of EIMD and improving recovery of muscle function in physically active females.

PURPOSE:The objective of this study is to verify the beneficial effects of whey protein (WP) supplementation on health promotion and enhance exercise performance in an aerobic-exercise training protocol.

METHODS:In total, 40 male Institute of Cancer Research mice (4 wk old) were divided into four groups (n = 10 per group): sedentary control with vehicle (SC) or WP supplementation (4.1 g·kg, SC + WP), and exercise training with vehicle (ET) or WP supplementation (4.1 g·kg, ET + WP). Animals in the ET and ET + WP groups underwent swimming endurance training for 6 wk, 5 d·wk. Exercise performance was evaluated by forelimb grip strength and exhaustive swimming time as well as by changes in body composition and biochemical parameters at the end of the experiment.

RESULTS:ET significantly decreased final body and muscle weight and levels of albumin, total protein, blood urea nitrogen, creatinine, total cholesterol, and triacylglycerol. ET significantly increased grip strength; relative weight (%) of liver, heart, and brown adipose tissue (BAT); and levels of aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, lactate dehydrogenase, creatine kinase, and total bilirubin. WP supplementation significantly decreased final body, muscle, liver, BAT, and kidney weight and relative weight (%) of muscle, liver, and BAT as well as levels of aspartate aminotransferase, lactate dehydrogenase, creatine kinase, and uric acid. In addition, WP supplementation slightly increased endurance time and significantly increased grip strength and levels of albumin and total protein.

CONCLUSION:WP supplementation improved exercise performance, body composition, and biochemical assessments in mice and may be an effective ergogenic aid in aerobic exercise training.