Fasting Before Evening Exercise Reduces Net Energy Intake and Increases Fat Oxidation, but Impairs Performance in Healthy Males and Females

Abstract

Acute morning fasted exercise may create a greater negative 24-hr energy balance than the same exercise performed after a meal, but research exploring fasted evening exercise is limited. This study assessed the effects of 7-hr fasting before evening exercise on energy intake, metabolism, and performance. Sixteen healthy males and females (n = 8 each) completed two randomized, counterbalanced trials. Participants consumed a standardized breakfast (08:30) and lunch (11:30). Two hours before exercise (16:30), participants consumed a meal (543 ± 86 kcal; FED) or remained fasted (FAST). Exercise involved 30-min cycling (∼60% VO2peak) and a 15-min performance test (∼85% VO2peak; 18:30). Ad libitum energy intake was assessed 15 min postexercise. Subjective appetite was measured throughout. Energy intake was 99 ± 162 kcal greater postexercise (p < .05), but 443 ± 128 kcal lower over the day (p < .001) in FAST. Appetite was elevated between the preexercise meal and ad libitum meal in FAST (p < .001), with no further differences (p ≥ .458). Fat oxidation was greater (+3.25 ± 1.99 g), and carbohydrate oxidation was lower (−9.16 ± 5.80 g) during exercise in FAST (p < .001). Exercise performance was 3.8% lower in FAST (153 ± 57 kJ vs. 159 ± 58 kJ, p < .05), with preexercise motivation, energy, readiness, and postexercise enjoyment also lower in FAST (p < .01). Fasted evening exercise reduced net energy intake and increased fat oxidation compared to exercise performed 2 hr after a meal. However, fasting also reduced voluntary performance, motivation, and exercise enjoyment. Future studies are needed to examine the long-term effects of this intervention as a weight management strategy.

Intermittent Fasting Promotes Weight Loss without Decreasing Performance in Taekwondo

“…Therefore, the lower TBM during fasting is acute if not associated with a negative energy balance [ 8 , 10 , 14 , 15 ]. However, the same sample size with different morphological profiles can have different results.…”

“…In eutrophic individuals, this strategy can decrease the TBM by 2% within a few weeks [ 6 ]. Such a lower TBM may result from behavioral and physiological changes that regulate appetite and result in lower caloric intake in the hours of fasting [ 7 ] that is not compensated in the non-restricted feeding period [ 8 ].…”

Fasting reduces satiety and increases hunger but does not affect the performance in resistance training

“…Slater et al [ 11 ] found that fasting before evening exercise was associated with reduced motivation and exercise enjoyment. Furthermore, Naharudin et al [ 10 ] and Stratton et al [ 7 ] identified a reduction in general disposition and poor mood in fasting conditions.…”

“…In contrast, Naharudin et al [ 9 ] discovered that fasting reduces the maximum number of repetitions (MNR) acutely performed in the back squat during the fasting state (10–13 h overnight) in trained individuals who skipped breakfast. Some studies identified bad mood and reduction in general disposition, motivation and exercised enjoyment in training in fasting conditions [ 7 , 10 , 11 ]. Diminished levels of blood glucose and increased cortisol levels may be considered the main factors contributing to the negative affective state and the decrease in overall mood and pleasure experienced during physical exercise while fasting [ 7 , 10 , 11 ].…”

“…Some studies identified bad mood and reduction in general disposition, motivation and exercised enjoyment in training in fasting conditions [ 7 , 10 , 11 ]. Diminished levels of blood glucose and increased cortisol levels may be considered the main factors contributing to the negative affective state and the decrease in overall mood and pleasure experienced during physical exercise while fasting [ 7 , 10 , 11 ]. Such factors could limit adherence to IF in the long term.…”