Effect of various whey protein supplements on recovery from prolonged endurance exercise in trained cyclists : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Nutritional Science at Massey University, Palmerston North, New Zealand
Background: Protein-containing recovery beverages are proposed to support an athlete's recovery from exercise through stimulation of insulin release, promoting the restoration of muscle glycogen stores, and stimulation of protein synthesis and muscle protein restoration. Objective: The present study aimed to determine, (1) whether there is an insulinotropic effect of whey proteins, when consumed in addition to carbohydrate, which is assumed to enhance muscle glycogen resynthesis and (2) whether a blend of hydrolysate and intact protein, when consumed in addition to carbohydrate, will enhance the athlete's recovery from exercise. Design: Twelve trained top level cyclists repeated a protocol on four consecutive weeks, during which either a control beverage (Carb) or three beverages containing whey protein (carbohydrate and intact protein (Carb + I); carbohydrate and protein hydrolysate (Carb + H; carbohydrate and intact protein : protein hydrolysate mix (Carb + M)) were consumed during recovery from exhaustive endurance exercise. The beverages were formulated to supply 1.2 g/kg/hour carbohydrate and 0.4 g/kg/hour protein. Subjects followed a controlled diet two days before each experimental day. On the experimental day the athletes each performed a glycogen-depleting exercise programme, then received the designated dietary beverage every 30 minutes for the first two hours post-exercise. The progress of recovery was monitored via the measurement of cardiovascular recovery, and the appearance and relative concentration of metabolites in blood (15 samples over a four hour period, obtained via an indwelling cannula) and urine samples (13 samples over a seven hour period) collected sequentially during the post-exercise recovery period. Results: Plasma albumin concentrations were significantly lower following consumption of beverages containing whey protein (Carb + H, p<0.01; Carb + M, p<0.05) compared to that observed with the Carb beverage. Urine output was significantly higher after consumption of the Carb beverage than with any of the three-protein containing beverages (Carb + I, p<0.01; Carb + H, p<0.05; Carb + M, p<0.05) during the period of controlled fluid consumption. Heart rate recovery was found to be significantly greater following consumption of the three protein-containing beverages (Carb + I, p<0.001; Carb + M, p<0.001, Carb + H, p<0.01) than following consumption of the Carb beverage. The Carb + M beverage produced increased heart rate recovery (p<0.001) compared to that observed following consumption of the other two protein-containing beverages (Carb + I, Carb + H). Following correction of the data for haematocrit, to account for the hydration status of the athletes, a significant difference (p<0.05) in the ratio of plasma insulin to plasma glucose concentrations was found following consumption of any of beverages containing whey protein (Carb + I, Carb + H, Carb + M) compared to that observed for the Carb beverage. Consumption of the Carb + I beverage resulted in significantly higher concentrations of urinary nitrogen excretion as urea (p<0.05) and ammonia (p<0.01), and significantly higher plasma concentrations of the amino acids Valine, Leucine, Isoleucine, Phenylalanine, Tryptophan, and Tyrosine (p<0.05). Conclusions: The addition of whey protein to a carbohydrate-containing beverage stimulated enhanced recovery from exercise. A major factor in the improved recovery was increased rehydration following consumption of the protein-containing beverages, mainly due to the high sodium content of these beverages. This increased rehydration was shown to influence results for plasma insulin and plasma glucose concentrations where, after accounting for the hydration status of athletes, a difference between consumption of the Carb beverage and that observed for any of the three protein-containing beverages was observed. The results also allude to a potential benefit of protein hydrolysates over intact protein on protein recovery. Consuming a protein mix (Carb + M) also appears to improve heart rate recovery compared to consuming either intact (Carb + I) or hydrolysed (Carb + H) proteins individually. The results of this study highlight the importance of dietary protein on enhancing recovery from endurance exercise.