Whey protein isolate reduces cortisol awakening response post-exercise

Introduction : Disruptions in cortisol awakening response (CAR), changes in Profile of Mood States (POMS), and decreases in heart rate variability (HRV) have been associated with fatigue and strenuous exercise. Whey protein isolate (WH) may improve stress responses. Purpose : To determine the effects of WH supplementation on CAR, POMS, and HRV after strenuous exercise. Methodology : Eleven recreationally active females (19 ± 2 yrs) completed a double-blinded, placebo-controlled crossover trial. Placebo (PL) was maltodextrin, and the intervention was 25 g of maltodextrin with 25 g of WH consumed prior to exercise. Exercise was 30 min at 70-75% VO 2peak (M = 21.7, SD = 0.1 ml/kg/min), 5 min rest, and 30 s Wingate anaerobic test (WAnT). HRV and POMS were recorded the following morning. Repeated measures ANOVA determined differences (p < .05) in 60 min salivary cortisol AUCg (CAR), POMS, HRV, and WAnT fatigue index (FI). Pearson’s correlation and multiple regression identified associations between CAR, POMS, HRV, and FI. Results : CAR was significantly different ( p = .033) between Placebo (33.4 ± 2.0 pg/dL*hr) and WH (30.9 ± 0.8 pg/dL*hr), with no significant differences in POMS, HRV, or FI. There was a significant correlation between POMS and FI on Day 3 during PL ( r = -.582, p = .030). Neither CAR, POMS, nor HRV was able to predict FI (all p > .05). Conclusions : Whey protein isolate may decrease CAR, but may have no effect on POMS, HRV, or FI, and no effect on short-duration sprint cycling performance. Limitations : WAnT performance was not affected; therefore, any association with reducing the physiological effects of central fatigue may be minimal. Practical applications may include a viable methodology for suppressing CAR in this type of participant.   Originality : The current study is unique in combining nutritional supplementation, exercise, and salivary cortisol post-exercise with female participants.