Journal Title (Medline/Pubmed accepted abbreviation): J Appl Physiol
Volume: Published ahead of print
doi (if applicable): 10.1152/japplphysiol.00577.2010 August 5, 2010
Summary of Background and Research Design
Hypothesis:A mixture of carbohydrate and protein supplementation will increase plasma volume and albumin levels during aerobic training, which will reduce heat and cardiovascular strain
Subjects:18 healthy, young males (mean age = 24 y, mean weight = 63 kg, mean BMI = 22 kg/m2); a total of 9 per group
Experimental design:Independent groups, blinded, not clear if treatment group assignment was random
Treatments and protocol:The subjects underwent a 5-day exercise protocol (cycling at 70% of VO2 max for 30 min/d) in which they took either a carbohydrate-protein supplement (CP) or a placebo (PL) 10 min after the end of the exercise for the day. The CP was a solution (6.4 mL/kg body weight) containing 56 kcal, 8.3 g carbohydrate, and 5.6 g protein per 100 mL). For a 63.6 kg subject, this works out to about 407 mL, 228 kcal, 34 g carbohydrate, and 23 g protein. The PL beverage was the same volume of a solution containing 15 kcal, 1.7 g carbohydrate, and 0 g protein per 100 mL). For the 63.6 kg subject, this worked out to 61 kcal and 7 g carbohydrate. The fat content of the solutions was not provided. The baseline diet of the subjects was about 2200 kcal and 90 g protein in each group (exclusive of the supplements). The authors measured cardiovascular parameters, peak oxygen consumption, plasma volume, and thermoregulatory responses.
Summary of research findings:
Plasma volume increased with both treatments from pre to post exercise training period. However, the CP caused a significantly larger increase in plasma volume than PL (7.4% vs, 3.9%, P = 0.009). Plasma albumin also significantly increased for the CP compared with no change in the PL group (between groups P<0.001). The 5-day exercise training period produced some degree of adaptive reduction in esophageal temperature in both groups, but the adaptive response was significantly more pronounced in the CP group relative to PL. A similar phenomenon was observed for the adaptive decline in heart rate during exercise from measurements taken before and after the training period-the CP supplement significantly enhanced this adaptation.
Interpretation of findings/Key practice applications:
The study indicates potential benefits from a carbohydrate-protein supplement in enhancing the physiological adaptations of the cardiovascular and thermoregulatory systems to aerobic exercise. A main probable explanation is the enhancement of the synthesis of proteins such as albumin that maintain oncotic pressure in the vascular space, leading to increased plasma volume. A key limitation to this study is that there was no comparison of the CP supplement to an isocaloric, carbohydrate-only beverage. Also, it is unknown if these benefits would translate to more highly trained subjects or to subjects with differing levels of baseline dietary protein intakes.