Chronic circadian disruption on a high-fat diet impairs glucose tolerance

Abstract

Background: Nearly 14% of Americans experience chronic circadian disruption due to shift work, increasing their risk of obesity, diabetes, and other cardiometabolic disorders. These disorders are also exacerbated by modern eating habits such as frequent snacking and consumption of high-fat foods.

Methods: We investigated the effects of recurrent circadian disruption (RCD) on glucose metabolism in C57BL/6 mice and in human participants exposed to non-24-h light-dark (LD) schedules vs. those on standard 24-h LD schedules. These LD schedules were designed to induce circadian misalignment between behaviors including rest/activity and fasting/eating with the output of the near-24-h central circadian pacemaker, while minimizing sleep loss, and were maintained for 12 weeks in mice and 3 weeks in humans. We examined interactions of these circadian-disrupted schedules compared to control 24-h schedules with a lower-fat diet (LFD, 13% in mouse and 25-27% in humans) and high-fat diet (HFD, 45% in mouse and 45-50% in humans). We also used young vs. older mice to determine whether they would respond differently to RCD.

Results: When combined with a HFD, we found that RCD caused significant weight gain in mice and increased body fat in humans, and significantly impaired glucose tolerance and insulin sensitivity in both mice and humans, but this did not occur when RCD was combined with a LFD. This effect was similar in both young and older mice.

Conclusion: These results in both humans and a model organism indicate that circadian disruption has an adverse effect on metabolism among individuals eating a high-fat Western-style diet, even in the absence of significant sleep loss, and suggest that reducing dietary fat may protect against the metabolic consequences of a lifestyle (such as shift work) that involves chronic circadian disruption.

Keywords: Glucose tolerance; High-fat diet; Insulin sensitivity; Recurrent circadian disruption; Shift work; Weight gain.

Figure 1.. Schematic illustration of animal study light-dark schedules.

Each horizontal bar represents 24 hours of the experiment, and subsequent days of the experiment are shown below the previous day. White and grey colors represent the light and dark episodes, respectively. While the study schedules were imposed for 12 weeks, only the first 6 days of the experiments are shown. (A) Light-dark schedule for the Control mice; (B) light-dark schedule for the RCD mice.

Figure 2.. Metabolic effects of RCD in young and old mice on LFD.

(A) Weight gain during the 12-week experimental interval, (B) daily food intake), and (C) fasting blood glucose levels in young (solid bars) and old (hashed bars) Controls on a 12:12-hour LD (green) and RCD mice on 10:10-hour LD cycle (blue). (D) Changes in blood glucose levels in response to 2 g/kg glucose IP (glucose tolerance) in Control and RCD mice, € the 120-minute blood glucose AUC. (F) Changes in blood glucose levels in response to insulin i.p (insulin sensitivity) in Control and RCD mice; (G) the 120-minute blood glucose AUC). P-values from mixed model ANOVAs are denoted with Bonferroni-adjusted p<0.05 *. Number of mice in each group: young RCD(LFD), n=8; old RCD(LFD), n=7; young Control(LFD), n=7; old Control(LFD), n=7.

Figure 3.. Metabolic effects of RCD in young and old mice on HFD.

(A) Daily food intake, (B) weight gain during the three month-experiment, and (C) fasting blood glucose levels in young (solid bars) and old (hashed bars) Control mice on a 12:12 LD cycle (green) and RCD mice on 10:10 LD cycle (blue). (D) Changes in blood glucose levels in response to 2 g/kg glucose i.p (glucose tolerance) in Control and RCD mice, and (E) the 120-minute blood glucose AUC. (F) Changes in blood glucose levels in response to insulin i.p (insulin sensitivity) for Control and RCD mice; (G) the 120-minute blood glucose AUC. P-values from mixed model ANOVAs are denoted with Bonferroni-adjusted p<0.05 *. Number of mice in each group: young RCD(LFD), n=8; old RCD(LFD), n=7; young Control(LFD), n=7; old Control(LFD), n=7.

Figure 4.. Human inpatient study schedules.

Study day is indicated along the left side and representative clock hour along the top axis. Solid black bars represent scheduled sleep episodes in darkness, while gray and white indicate parts of the study conducted under 4 lux and 90 lux lighting levels, respectively. Diagonal hatched bars indicate times during wake episodes when participants maintained a semi-recumbent posture in bed. The timing of standardized breakfast meal responses (green bars in Control group; blue bars in RCD group) for assessment of glucose and insulin is also indicated. Depicted schedules are for LFD groups.

Figure 5.. Postprandial glucose and insulin in humans on LFD.

Postprandial glucose and insulin profiles are depicted following a standardized breakfast meal at baseline (BL) and after exposure (EXP) to the RCD (panels A, C) or Control schedule (panels B, D). AUC values over the first 180 minutes following the meal at BL, EXP, and REC are shown for the RCD group (panels E, G) and Control group (panels F, H). Values shown are mean±SEM. Bonferroni-adjusted p-values from LSmeans post-hoc test are depicted as follows: p≤0.05 *, p≤0.01 **, p≤0.001 ***. Number of participants in each group: RCD(LFD), n=4; Control(LFD), n=4.

Figure 6.. Postprandial glucose and insulin in humans on HFD.

Postprandial glucose and insulin profiles are depicted following a standardized breakfast meal at baseline (BL) and after exposure (EXP) to the RCD (panels A, C) or Control schedule (panels B, D). AUC values over the first 180 minutes following the meal at BL, EXP, and REC are shown for the RCD group (panels E, G) and Control group (panels F, H). Values shown are mean±SEM Bonferroni-adjusted p-values from LSmeans post-hoc test are depicted as follows: p≤0.05 *, p≤0.01 **, p≤0.001 ***. Number of participants in each group: RCD(HFD), n=5; Control(HFD), n=4.