Effects of fasting on endurance exercise in adult males: preliminary evidence for a "nocebo" effect

Abstract

The literature has repeatedly reported a negative effect of fasting on endurance exercise in humans. The goal of this study was to test the hypothesis that endurance performance is susceptible to a “negative placebo” or “nocebo” effect of early (24-h) fasting. Twelve physically-fit, young adult males performed an endurance performance test under each of three conditions: after a 24-hour fast (A), after a 24-hour fast ingesting non-caloric liquid meals (B), and in the postabsorptive state (C). The tests consisted of pedalling the maximum distance in 60 minutes on a cycle ergometer at 2 kpm, and were separated by a minimum of one week. Subjects were allocated randomly to the different treatment condition orders. Plasma glucose and triglycerides were measured before and after each performance test. Performance was significantly lower (p<0.05) in A (29.19±5.2 km) than C (32.19±6.2 km). There was no significant difference between A or C, and B (30.57±5.5 km). Subjects were euglycemic both before and after the tests under all three conditions. Triglyceride levels were higher before the test in condition C (p<0.05). Individual performances showed two distinct subgroups in this sample. For “susceptible” subjects, C>A and A<B (p<0.05); “non-susceptibles” showed A=B=C.Existen múltiples publicaciones que reportan un efecto negativo del ayuno sobre el ejercicio de resistencia en humanos. El propósito de este estudio fue probar la hipótesis de que el rendimiento deportivo de resistencia es susceptible a un efecto "placebo negativo" o "nocebo", producido por el ayuno corto de 24 horas.