Seven healthy men (aged 22.4 ¡À 0.4 years) participated in this study, which involved delaying mealtimes by 5 h for two weeks. Prior to this study, the regular mealtimes of participants were at 08:00, 13:00, and 18:00 (Baseline). During the intervention, each meal was provided at 13:00, 18:00 and 23:00 (Late mealtimes). Circadian variation was assessed by HRV based on R-R intervals calculated from a pulse at the rising phase of each spike in the QRS complex in a 24-h electrocardiograph record. The ratio of low frequency (LF) to high frequency (HF) power (LF/HF) and the ratio of HF power to total power ( % HF) were calculated using spectral analysis. The phase and amplitude of HRV variables in a 24-h period were mathematically obtained with double cosinor analysis.
The acrophase and amplitude for LF power, HF power and % HF in a 24-h period were not significantly different between Baseline and Late mealtimes. On the other hand, the acrophase significantly differed between Baseline and Late mealtimes for heart rate (95 % CI, 1.1-3.8 h), standard deviation of R-R intervals (95 % CI, 2.5-4.4 h) and LF/HF (95 % CI, 1.1-2.3 h).
Our findings suggest that delayed mealtimes shift the phase of circadian rhythm of the autonomic nervous system.