Author(s): ARETA, J., JONES, R., SAUNDERS, B., MORTON, J., GEJL, K., NIELSEN, J., LOUIS, J., Institution: LIVERPOOL JOHN MOORES UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 1408

INTRODUCTION:
Carbohydrate loading (CL) has been widely promoted for more than 50 years as a nutritional strategy to enhance endurance performance, yet its efficacy remains uncertain. Reported performance improvements of approximately 3 percent in exercise lasting longer than 90 minutes may be influenced by expectation and belief, as few studies appear to have employed double-blind, placebo-controlled (DBPC) designs. Furthermore, the role of in-exercise carbohydrate provision is inconsistently addressed, despite its established effects on endurance performance.
METHODS:
We systematically examined the literature to determine the use of blinding and in-exercise carbohydrate intake in CL research. We conducted a search in five online databases that yielded 10,422 studies that went through a systematic selection. We identified all studies involving an endurance exercise performance test lasting ≥90 min, that compared a moderate or ‘normal’ carbohydrate intake (~4–6 g/kg/day) with an above-normal or high intake (>7 g/kg/day) for at least 24 hours.
RESULTS:
Fourteen studies were identified using these criteria. These studies showed substantial heterogeneity in study design, including differences in achieved muscle glycogen levels, exercise test modality, and test duration. Only two studies used DBPC designs, and only four studies provided carbohydrates during exercise. Both DBPC studies included in-exercise carbohydrate provision and reported no performance benefit of CL. Among the two additional studies that provided carbohydrates during exercise but were not DBPC, CL was associated with small-to-moderate performance improvements (Cohen's d = 0.31 to 0.40), effect sizes comparable to those typically reported for placebo-based nutritional interventions. Nonetheless, comparison of blinded and non-blinded studies is limited by substantial differences in study design.
CONCLUSION:
Taken together, the available evidence suggests that once placebo effects are controlled for and in-exercise carbohydrate intake is optimised, the independent ergogenic effect of CL is unclear. These findings highlight the historical limitations of CL research designs and suggest that belief and expectation may contribute to reported performance benefits. Future studies using rigorous DBPC designs are required to isolate the true physiological effects of CL from placebo effects in endurance performance.