Exercise prior to a freely requested meal modifies pre and postprandial glucose profile, substrate oxidation and sympathovagal balance

Abstract

BackgroundThe effects of exercise on glucose and metabolic events preceding and following a freely initiated meal have never been assessed. Moreover, the relationship between these events and sympathovagal balance is not known. The objective of this study was to determine whether exercise prior to a freely requested meal modifies the pre- and postprandial glucose profile, substrate oxidation and sympathovagal balance.MethodsNine young active male subjects consumed a standard breakfast (2298 ± 357 kJ). After 120 min, they either performed 75 min of exercise on a cycle ergometer (EX - 70% VO2max) or rested (RT). Lunch was freely requested but eaten ad libitum only during the 1st session, and then energy intake was fixed across conditions. Glucose and sympathovagal balance were assessed continuously using a subcutaneous glucose monitoring system and analysis of heart rate variability, respectively. Every 5 min, a mean value was calculated for both glucose and sympathovagal balance. Substrate oxidation was determined by calculating the gas exchange ratio when lunch was requested and 180 min after the onset of eating.ResultsPreprandial glucose profiles were found in 72% of the sessions and with a similar frequency under both conditions. Meals were requested after a similar delay (40 ± 12 and 54 ± 10 min in EX and RT respectively; ns). At meal request, sympathovagal balance was not different between conditions but CHO oxidation was lower and fat oxidation higher in EX than in RT (-46% and +63%, respectively; both p < 0.05). Glucose responses to the meal were higher in incremental (+ 48%) but not in absolute value in EX than in RT, with a higher fat oxidation (+ 46%, p < 0.05), and a greater vagal withdrawal (+ 15%, p < 0.05).ConclusionsThese results show that exercise does not impair preprandial glucose declines at the following meal freely requested, but leads to an increased postprandial glucose response and an elevated fat oxidation, an effect that vagal withdrawal may contribute to explain.

Exercising for Metabolic Control: Is Timing Important?

“…A more vigorous postprandial exercise has been reported to transiently increase blood glucose values compared to pre-exercise [52]. In contrast, Charlot et al [37] reported that 75 min of high-intensity cycling, compared to rest, yield sustained lower glycemia throughout the exercise session and may also exert an influence on the following meal, delaying peak postlunch glycemia with no significant difference in total glucose AUCs. However, the generalizability and practical relevance of such results may need further investigation.…”

“…The remaining 18 studies investigated the effect of exercise on postprandial events, modulating some parameters related to meals and exercise (i.e. exercise intensity and duration, meal size and composition) [36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53]. …”

Noninvasive measurements to evaluate the effects of military training on the human autonomic nervous system

“…Whereas exercise training lasting for weeks or months was shown to have no impact on HRV [27], cause an increase in HRV [26,28], or lead to decreased LF and increased HF [29]. Moreover, the change in LF/ HF ratio after exercise also varied: some found that it shifted to a sympathetic dominance [25], some reported a parasympathetic activation [30], or that there was no significant change [28]. Populationbased studies have shown that leisure time physical activity of greater intensity is associated with higher levels of LF and HF [31].…”

“…Although HRV is an established method to assess autonomic innervation of the heart, the effects of exercise on HRV vary widely. Moderate exercise was reported to cause a reduction in the high-frequency component (HF) [23], in both the HF and lowfrequency component (LF) [25], in HRV as a whole [26], or no significant change in HF [2]. Whereas exercise training lasting for weeks or months was shown to have no impact on HRV [27], cause an increase in HRV [26,28], or lead to decreased LF and increased HF [29].…”

Comparison of energy-matched high-intensity interval and moderate-intensity continuous exercise sessions on latency to eat, energy intake, and appetite

“…The end of the exercise occurred 120 min after the completion of breakfast and was designated t120. According to our previously described procedure (Charlot et al 2011), the participant was then placed in an isolated room deprived of time cues (no computer, smartphone, or watch) and had to spontaneously request his lunch by pressing the button of a visual alarm when he felt the need to eat.…”