The impact of meal timing on performance, sleepiness, gastric upset, and hunger during simulated night shift

Abstract

This study examined the impact of eating during simulated night shift on performance and subjective complaints. Subjects were randomized to eating at night (n=5; 23.2 ± 5.5 y) or not eating at night (n=5; 26.2 ± 6.4 y). All participants were given one sleep opportunity of 8 h (22:00 h-06:00 h) before transitioning to the night shift protocol. During the four days of simulated night shift participants were awake from 16:00 h-10:00 h with a daytime sleep of 6 h (10:00 h-16:00 h). In the simulated night shift protocol, meals were provided at ≈0700 h, 1900 h and 0130 h (eating at night); or ≈0700 h, 0930 h, 1410 h and 1900 h (not eating at night). Subjects completed sleepiness, hunger and gastric complaint scales, a Digit Symbol Substitution Task and a 10-min Psychomotor Vigilance Task. Increased sleepiness and performance impairment was evident in both conditions at 0400 h (p<0.05). Performance impairment at 0400 h was exacerbated when eating at night. Not eating at night was associated with elevated hunger and a small but significant elevation in stomach upset across the night (p<0.026). Eating at night was associated with elevated bloating on night one, which decreased across the protocol. Restricting food intake may limit performance impairments at night. Dietary recommendations to improve night-shift performance must also consider worker comfort.

Keywords: Circadian misalignment; Hunger; Performance; Psychomotor vigilance; Shift-work; Sleep loss; Sleepiness; Timed eating.

Fig. 1.

Protocol schematic. Black bars; scheduled sleep opportunities, white bars; periods of wake, patterned box; blood testing in response to breakfast meal, grey box; meal times, open black bar; neurobehavioral test battery, PRE; pre night shift, NS1-4; night shift work days, RTDS; return to day shift.

Fig. 2.

Consort diagram of participants who were screened, allocated a condition, completed the laboratory protocol and data analysed.

Fig. 3.

Performance following simulated night-shift. A-PVT Lapses, B- PVT Errors, C- PVT Median Response Time, D- Digit Symbol Substitution Task (DSST) number correct. Eating at night condition- solid black marker, not eating at night condition-open grey circle marker. Bars represent standard error.

Fig. 4.

Hunger ratings following simulated night-shift. A-hungry, B- full, C- thoughts of food, D- urge to eat. Eating at night condition- solid black marker, not eating at night condition-open grey circle marker. Bars represent standard error. Dash line represents neutral on the rating scale.

Fig. 5.

Gut reaction following simulated night-shift. A-Gassy, B- Upset stomach, C- Bloated, D- Dizzy. Eating at night condition- solid black marker, not eating at night condition- open grey circle marker. Bars represent standard error. Dash line- represents neutral on the rating scale.

Fig. 6.

Sleepiness following simulated night-shift. KSS: Karolinska Sleepiness Scale. Eating at night condition- solid black marker, not eating at night condition- open grey circle marker. Bars represent standard error.