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Food and Sleep – Interactions of exercise and our daily schedule

Comment by Nicolle Kraenkel, EACPR Exercise, Basic and Translational Research Section


While no one now doubts the benefits of exercise training, exercise modalities are still in the process of being optimised for various patient groups. Apart from exercise intensity, frequency, duration and type of exercise, its interaction with the circadian rhythm as well as meal-induced metabolic changes might be another point relevant to exercise efficiency.

Two recent papers have dealt with the question when to exercise best, employing different target parameters: nocturnal blood pressure (BP) decrease (“dipping”) and sleep architecture in obese prehypertensive patients [1], as well as various metabolic parameters in obese patients with type 2 diabetes [2].

In the study by Fairbrother et al. [1], twenty overweight, prehypertensive patients were performing exercise training sessions either in the morning (7 a.m.), at mid-day (1 p.m.) or in the evening (7 p.m.), with BP monitoring during the following night. Total sleep time did not differ between groups, but intriguingly, morning exercise did result in a significant improvement of systolic as well as diastolic night-time BP, as well as restoration of BP dipping. Morning exercise also increased the time spent in deep sleep and reduced sleep latency. While mid-day exercise did not result in any improvement in the parameters assessed, evening exercise might also have some potential. Though evening training did improve BP dipping and sleep-on latency, BP changes did not achieve significance in this study.

However, this might be due to the rather small, heterogeneous study cohort. The study did not explain why the early morning time point might be the most beneficial for improvement of BP and sleep by exercise, one might speculate that both, morning and evening sessions fall in a time with usually reduced physical activity and would therefore prolong the duration of physical activity during the day. Mid-day exercise would fall into a more active time of day, therefore providing less addition to total active time per day. In addition, exercise time would likely influence circadian metabolic and hormone changes.

Heden et al. [2] investigated the effect of resistance exercise performed prior to or after the consumption of a standard meal, as compared to the consumption of the meal without exercise.

Each participant performed all three protocols at different occasions in random order. Pre- as well as post-prandial exercise were effective in reducing glucose and insulin levels, albeit via different mechanisms.

Interestingly, in the post-prandial exercise protocol, glucose lowering was only effective during the actual exercise session and rebounded to post-meal no-exercise levels at the cessation of exercise, potentially due to a transient increase in hepatic glucose release post-exercise [3]. Instead, only post-prandial exercise did reduce triacylglycerol (TAG) levels, mainly due to lowering of VLDL1 (Very Low Density Lipoprotein 1), therefore indicating that post-prandial resistance exercise might potentially be more effective in reducing cardiovascular risk.

Finally, the authors state that improvements in glucose levels are transient in both exercise protocols, requiring daily exercise sessions. Thus, they underline an important point seen with many exercise-mediated mechanisms “exercise cannot be stored” and needs to be performed regularly in order to exert its beneficial effect on the cardiovascular system.

3) The effect of moderate exercise on postprandial glucose homeostasis in NIDDM patients.
J.J. Larsen et al.
Diabetologia 1997; 40: 447-453