Food intake during the normal activity phase prevents obesity and circadian desynchrony in a rat model of night work

Fasting as an intervention to alter the impact of simulated night-shift work on glucose metabolism in healthy adults: a cluster randomised controlled trial

AIMS/HYPOTHESIS

Night-shift work causes circadian misalignment and impairs glucose metabolism. We hypothesise that food intake during night shifts may contribute to this phenomenon.

METHODS

This open-label, multi-arm, single-site, parallel-group controlled trial involved a 6 day stay at the University of South Australia's sleep laboratory (Adelaide, SA, Australia). Healthy, non-shift-working adults without obesity (N=55; age 24.5 ± 4.8 years; BMI 24.8 ± 2.8 kg/m2) were assigned to the next available run date and cluster randomised (1:1:1) to fasting-at-night (N=20), snack-at-night (N=17), or meal-at-night (N=18) conditions. One participant withdrew from each group, prior to starting the study. Due to study design, neither participants nor people collecting their measurements could be blinded. Statistical and laboratory staff were concealed to study allocation. Participants were fed at calculated energy balance, with the macronutrient composition of meals being similar across conditions. The primary outcomes were a linear mixed-effects model of glucose, insulin and NEFA AUC in response to a 75 g OGTT that was conducted prior to and after 4 consecutive nights of shift work plus 1 night of recovery sleep. Insulin sensitivity, insulinogenic and disposition indexes were also calculated.

RESULTS

Night-shift work impaired insulin sensitivity, as measured by insulin AUC (p=0.035) and the insulin sensitivity index (p=0.016) across all conditions. Insulin secretion, as measured by the insulinogenic index, was increased in the fasting-at-night condition only (p=0.030), resulting in a day×condition interaction in glucose AUC (p<0.001) such that glucose tolerance was impaired in the meal-at night (+2.00 [95% CI 1.45, 2.56], p<0.001) and snack at-night (+0.96 [0.36, 1.56], p=0.022) conditions vs the fasting-at-night (+0.34 [-0.21, 0.89]) condition. A day×condition interaction was also observed in NEFA AUC (p<0.001), being higher in the meal-at-night (+0.07 [0.03, 0.10]. p=0.001) and snack-at-night (0.01 [-0.03, 0.05], p=0.045) conditions vs the fasting-at-night condition (-0.02 [-0.06, 0.01]). No adverse events occurred.

CONCLUSIONS/INTERPRETATION

The timing of food intake has a critical effect on glucose metabolism during simulated night-shift work, which was readily amendable to a meal re-timing intervention.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry (ANZCTR) ACTRN12616001556437 FUNDING: This work was funded by the National Health and Medical Research Council (NHMRC), APP1099077.

Effects of Intermittent Fasting on Female Reproductive Function: A Review of Animal and Human Studies

PURPOSE OF REVIEW

Intermittent fasting has gained significant attention, yet a comprehensive understanding of its impact on female reproductive health is lacking. This review aims to fill this gap by examining various intermittent fasting regimens and their effects on female reproductive function, along with potential mechanisms.

RECENT FINDINGS

In healthy non-overweight/obese or pregnant animal models, alternate-day fasting (ADF) and an 8-h time-restricted feeding (TRF) window may have adverse effects on reproductive function. However, these regimens show potential to mitigate negative consequences induced by a high-fat diet (HFD) or environmental exposure. A 10-h TRF demonstrates benefits in improving fertility in both normal-weight and HFD-fed animal models. In women with overweight/obesity or polycystic ovary syndrome (PCOS), the 5:2 diet and TRF significantly reduce the free androgen index while elevating sex hormone binding globulin, promising improvements in menstrual regulation. For pregnant Muslim women, available data do not strongly indicate adverse effects of Ramadan fasting on preterm delivery, but potential downsides to maternal weight gain, neonatal birthweight, and long-term offspring health need consideration. Factors linking intermittent fasting to female reproductive health include the circadian clock, gut microbiota, metabolic regulators, and modifiable lifestyles. Drawing definitive conclusions remains challenging in this evolving area. Nonetheless, our findings underscore the potential utility of intermittent fasting regimens as a therapeutic approach for addressing menstruation irregularities and infertility in women with obesity and PCOS. On the other hand, pregnant women should remain cognizant of potential risks associated with intermittent fasting practices.

Work Around the Clock: How Work Hours Induce Social Jetlag and Sleep Deficiency

A growing body of evidence has placed an increasing emphasis on how sleep affects health. Not only does insufficient sleep make one subjectively feel worse, but is associated with chronic diseases that are considered epidemics in industrialized nations. This is partly caused by the growing need for prolonged work and social schedules, exemplified by shift work, late-night weekends, and early morning work/school start times (social jetlag). Here, we consider fundamental relationships between the circadian clock and biologic processes and discuss how common practices, such as shift work and social jetlag, contribute to sleep disruption, circadian misalignment, and adverse health outcomes.

Impact of Sleeve Gastrectomy on Body Weight and Food Intake Regulation in Diet-Induced Obese Mice

The epidemic of obesity has increased worldwide and is associated with comorbidities such as diabetes and cardiovascular disease. In this context, strategies that modulate body weight and improve glycemic metabolism have increased, and bariatric surgeries such as Sleeve Gastrectomy (SG) have been highlighted in obesity treatment. However, the mechanism by which SG reduces body weight and improves glycemic control remains unknown. Thus, in this study, we aimed to evaluate food intake and the expression of hypothalamic genes involved with the regulation of this process in diet-induced obese mice submitted to SG. For this, we used C57BL/6 mice submitted to a 10-week high-fat diet protocol and submitted to SG. Food intake, fed and fasted glycemia, as well as hypothalamic anorexigenic and orexigenic gene expression were evaluated 4 weeks after the surgical procedure. First, we observed that SG reduces body weight (44.19 ± 0.47 HFD, 43.51 ± 0.71 HFD-SHAM, and 38.22 ± 1.31 HFD-SG), fasting glycemia (115.0 ± 4.60 HFD, 122.4 ± 3.48 HFD-SHAM, and 93.43 ± 4.67 HFD-SG), insulinemia (1.77 ± 0.15 HFD, 1.92 ± 0.27 HFD-SHAM, and 0.93 ± 0.05 HFD-SG), and leptinemia (5.86 ± 1.38 HFD, 6.44 ± 1.51 HFD-SHAM, and 1.43 ± 0.35 HFD-SG) in obese mice. Additionally, SG reduces food (5.15 ± 0.18 HFD, 5.49 ± 0.32, HFD-SHAM, and 3.28 ± 0.26 HFD-SG) and total (16.88 ± 0.88 HFD, 17.05 ± 0.42, HFD-SHAM, and 14.30 ± 0.73 HFD-SG) calorie intake without alterations in anorexigenic and orexigenic gene expression. In conclusion, these data indicate that SG improves obesity-associated alterations at least in part by a reduction in food intake. This effect is not associated with the canonical food intake pathway in the hypothalamus, indicating the involvement of non-canonical pathways in this process.

Night shift-induced circadian disruption: links to initiation of non-alcoholic fatty liver disease/non-alcoholic steatohepatitis and risk of hepatic cancer

The circadian system plays a crucial role in regulating metabolic homeostasis at both systemic and tissue levels by synchronizing the central and peripheral clocks with exogenous time cues, known as zeitgebers (such as the light/dark cycle). Our body's behavioral rhythms, including sleep-wake cycles and feeding-fasting patterns, align with these extrinsic time cues. The body cannot effectively rest and repair itself when circadian rhythms are frequently disrupted. In many shift workers, the internal rhythms fail to fully synchronize with the end and start times of their shifts. Additionally, exposure to artificial light at night (LAN), irregular eating patterns, and sleep deprivation contribute to circadian disruption and misalignment. Shift work and jet lag disrupt the normal circadian rhythm of liver activity, resulting in a condition known as "circadian disruption". This disturbance adversely affects the metabolism and homeostasis of the liver, contributing to excessive fat accumulation and abnormal liver function. Additionally, extended working hours, such as prolonged night shifts, may worsen the progression of non-alcoholic fatty liver disease (NAFLD) toward non-alcoholic steatohepatitis (NASH) and increase disease severity. Studies have demonstrated a positive correlation between night shift work (NSW) and elevated liver enzymes, indicative of hepatic metabolic dysfunction, potentially increasing the risk of hepatocellular carcinoma (HCC) related to NAFLD. This review consolidates research findings on circadian disruption caused by NSW, late chronotype, jet lag, and social jet lag, drawing insights from studies involving both humans and animal models that investigate the effects of these factors on circadian rhythms in liver metabolism.

Eating Around the Clock: Circadian Rhythms of Eating and Metabolism

The time of day that we eat is increasingly recognized as contributing as importantly to overall health as the amount or quality of the food we eat. The endogenous circadian clock has evolved to promote intake at optimal times when an organism is intended to be awake and active, but electric lights and abundant food allow eating around the clock with deleterious health outcomes. In this review, we highlight literature pertaining to the effects of food timing on health, beginning with animal models and then translation into human experiments. We emphasize the pitfalls and opportunities that technological advances bring in bettering understanding of eating behaviors and their association with health and disease. There is great promise for restricting the timing of food intake both in clinical interventions and in public health campaigns for improving health via nonpharmacological therapies.

Association between dinner-bedtime interval and type 2 diabetes mellitus: a large-scale cross-sectional study

Objective

Glucose metabolism is impacted by circadian disruption. Dinner-bedtime interval (DBI) was an accessible indicator to reflect the alignment between dinner time and circadian clock. We aimed to investigate the association of DBI with type 2 diabetes mellitus (T2DM).

Methods

7676 adult subjects from the Henan Rural Cohort were included. Their demographic information including dinner time and bedtime was collected. Fasting venous blood samples were collected for biochemical determinations. Generalized linear regression model was used to analyze the factors influencing DBI. Furthermore, logistic regression incorporated with restricted cubic spline model was applied to evaluate the association between DBI and T2DM.

Results

The results of multiple linear regression model showed that age (β: -0.018, 95% CI: -0.021, -0.015) was negatively correlated with DBI. Female (β: 0.311, 95% CI: 0.229, 0.393), junior high school education (β: 0.246, 95% CI: 0.187, 0.306), high school education or above (β: 0.346, 95% CI: 0.259, 0.433), average monthly income with 1000-1999 CNY(0.102, 95% CI: 0.032, 0.171), average monthly income ≥ 2000 CNY (β: 0.164, 95% CI: 0.076, 0.251), moderate physical activity (β: 0.134, 95% CI: 0.071, 0.197), current smokers (β: 0.214, 95% CI: 0.118, 0.309), current drinkers (β: 0.099, 95% CI: 0.008, 0.190) were positively correlated with DBI. Furthermore, DBI was significantly associated with T2DM (adjusted OR: 0.910, 95%CI: 0.845-0.979, P = 0.012). DBI longer than 3 h was associated with decreased risk of T2DM (adjusted OR: 0.773, 95%CI: 0.648-0.921, P = 0.004).

Conclusions

DBI larger than 3 h is beneficial to T2DM prevention. Further investigation is required to verify the association.

Deletion of the Clock Gene Bmal2 Leads to Alterations in Hypothalamic Clocks, Circadian Regulation of Feeding, and Energy Balance

BMAL2 (ARNTL2) is a paralog of BMAL1 that can form heterodimers with the other circadian factors CLOCK and NPAS2 to activate transcription of clock and clock-controlled genes. To assess a possible role of Bmal2 in the circadian regulation of metabolism, we investigated daily variations of energy metabolism, feeding behavior, and locomotor behavior, as well as ability to anticipate restricted food access in male mice knock-out for Bmal2 (B2KO). While their amount of food intake and locomotor activity were normal compared with wild-type mice, B2KO mice displayed increased adiposity (1.5-fold higher) and fasted hyperinsulinemia (fourfold higher) and tended to have lower energy expenditure at night. Impairment of the master clock in the suprachiasmatic nuclei was evidenced by the shorter free-running period (-14 min/cycle) of B2KO mice compared with wild-type controls and by a loss of daily rhythmicity in expression of intracellular metabolic regulators (e.g., Lipoprotein lipase and Uncoupling protein 2). The circadian window of eating was longer in B2KO mice. The circadian patterns of food intake and meal numbers were bimodal in control mice but not in B2KO mice. In response to restricted feeding, food-anticipatory activity was almost prevented in B2KO mice, suggesting altered food clock that controls anticipation of food availability. In the mediobasal hypothalamus of B2KO mice, expression of genes coding orexigenic neuropeptides (including Neuropeptide y and Agouti-Related Peptide) was downregulated, while Lipoprotein lipase expression lost its rhythmicity. Together, these data highlight that BMAL2 has major impacts on brain regulation of metabolic rhythms, sleep-wake cycle, and food anticipation.

Circadian desynchrony and glucose metabolism

The circadian timing system controls glucose metabolism in a time-of-day dependent manner. In mammals, the circadian timing system consists of the main central clock in the bilateral suprachiasmatic nucleus (SCN) of the anterior hypothalamus and subordinate clocks in peripheral tissues. The oscillations produced by these different clocks with a period of approximately 24-h are generated by the transcriptional-translational feedback loops of a set of core clock genes. Glucose homeostasis is one of the daily rhythms controlled by this circadian timing system. The central pacemaker in the SCN controls glucose homeostasis through its neural projections to hypothalamic hubs that are in control of feeding behavior and energy metabolism. Using hormones such as adrenal glucocorticoids and melatonin and the autonomic nervous system, the SCN modulates critical processes such as glucose production and insulin sensitivity. Peripheral clocks in tissues, such as the liver, muscle, and adipose tissue serve to enhance and sustain these SCN signals. In the optimal situation all these clocks are synchronized and aligned with behavior and the environmental light/dark cycle. A negative impact on glucose metabolism becomes apparent when the internal timing system becomes disturbed, also known as circadian desynchrony or circadian misalignment. Circadian desynchrony may occur at several levels, as the mistiming of light exposure or sleep will especially affect the central clock, whereas mistiming of food intake or physical activity will especially involve the peripheral clocks. In this review, we will summarize the literature investigating the impact of circadian desynchrony on glucose metabolism and how it may result in the development of insulin resistance. In addition, we will discuss potential strategies aimed at reinstating circadian synchrony to improve insulin sensitivity and contribute to the prevention of type 2 diabetes.

The effects of fasting compared to eating a meal or snack during simulated night shift on changes in metabolism associated with circadian misalignment: a protocol and methods paper

Study Objectives

This protocol paper outlines the methods that will be used to examine the impact of altering meal timing on metabolism, cognitive performance, and mood during the simulated night shift.

Methods

Participants (male and female) will be recruited according to an a priori selected sample size to complete a 7-day within and between participant's laboratory protocol. Participants will be randomly assigned to one of the three conditions: meal at night or snack at night or no meal at night. This protocol includes an 8-hour nighttime baseline sleep, followed by 4 consecutive nights of simulated nightshift (7 hours day sleep; 10:00-17:00 hours), and an 8-hour nighttime sleep (return to dayshift). During the simulated night shift, meals will be provided at ~06:30, 09:30, 14:10, and 19:00 hours (no eating at night); ~06:30, 19:00, and 00:30 hours (meal at night); or ~06:30, 14:10, 19:00, and 00:30 hours (snack at night). Meal composition will be strictly controlled throughout the study (45%-65% carbohydrates, 15%-25% protein, and 20%-35% fat per day) with daily energy provided to meet individual needs using the Harris-Benedict equation (light/sedentary activity). The primary outcome measures are serum concentrations of blood glucose, insulin, and free fatty acids area under the curve in response to the oral glucose tolerance test. Mixed-effect ANOVAs will be conducted.

Conclusions

This protocol paper describes a methodology to describe an innovative approach to reduce the metabolic disease impact associated with shift work.

Early chronotype favors appetite and reduced later day caloric intake among adults with obesity

Late chronotype (LC) is related to obesity and altered food intake throughout the day. But whether appetite perception and gut hormones differ among chronotypes is unclear. Thus, we examined if early chronotype (EC) have different appetite responses in relation to food intake than LC. Adults with obesity were categorized using the Morningness-Eveningness Questionnaire (MEQ) as either EC (n = 21, 18F, MEQ = 63.9 ± 1.0, 53.7 ± 1.2 yr, 36.2 ± 1.1 kg/m2) and LC (n = 28, 24F, MEQ = 47.2 ± 1.5, 55.7 ± 1.4 yr, 37.1 ± 1.0 kg/m2). Visual analog scales were used during a 120 min 75 g oral glucose tolerance test (OGTT) at 30 min intervals to assess appetite perception, as well as glucose, insulin, GLP-1 (glucagon-like polypeptide-1), GIP (glucose-dependent insulinotrophic peptide), PYY (protein tyrosine tyrosine), and acylated ghrelin. Dietary intake (food logs), resting metabolic rate (RMR; indirect calorimetry), aerobic fitness (maximal oxygen consumption (VO2max)), and body composition dual-energy X-ray absorptiometry (DXA) were also assessed. Age, body composition, RMR, and fasting appetite were similar between groups. However, EC had higher satisfaction and fullness as well as reduced desires for sweet, salty, savory, and fatty foods during the OGTT (P <0.05). Only GIP tAUC0-120 min was elevated in EC versus LC (p = 0.01). Daily dietary intake was similar between groups, but EC ate fewer carbohydrates (p = 0.05) and more protein (p = 0.01) at lunch. Further, EC had lower caloric (p = 0.03), protein (p = 0.03) and fat (p = 0.04) intake during afternoon snacking compared to LC. Dietary fat was lower, and carbohydrates was higher, in EC than LC (p = 0.05) at dinner. Low glucose and high insulin as well as GLP-1 tAUC60-120 min related to desires for sweet foods (p < 0.05). Taken together, EC had more favorable appetite and lower caloric intake later in the day compared with LC.

Comparison of three methods of intermittent fasting in high-fat-diet-induced obese mice

Purpose

Intermittent fasting (IF), describes a variety of diets that the individual is exposed to intermittent periods of fasting and refeeding. The present study was designed to compare the three most popular intermittent fasting methods in high-fat-diet-induced obese mice.

Methods

50 male C57BL/6 mice were divided into Normal Control (CN), High-Fat Control (CH), IF1 (Alternate Day Fasting), IF2 (Time-Restricted Feeding), IF3 (5:2 Diet) diets. In the first phase of the study, the mice were fed ad libitum either with a 54% Calorie high-fat (CH, IF1, IF2, IF3) or standard CHOW (CN) for 8 weeks. Then, in the intervention phase, the IF groups were fasted for four weeks based on their fasting protocol. At the end of the study, the mice fasting blood, liver and fat tissue samples were biochemically and pathologically assessed.

Results

The weight loss during the fasting period in IF1 and IF2 groups was significantly greater than CH. The epididymal fat pad weight was significantly lower in IF2 and IF3 compared to CH. The serum Triglyceride was significantly greater in CH than in the CN group. The tissue injury scores of the high-fat-diet groups were significantly greater than CN. Also, the tissue injury score was greater in IF1 group compared to the high-fat control group.

Conclusion

All of the fasting protocols can prompt acceptable energy restriction and the ADF and TRF protocols can significantly cause weight loss. Also, the TRF and 5:2 Diets can lower the visceral adiposity. However further human studies focusing on dietary adherence seem necessary.

The association between outdoor light at night exposure and adult obesity in Northeastern China

Previous studies have linked exposure to light at night (LAN) with various health outcomes, but evidence is limited for the LAN-obesity association. Thestudy analysed data from 24,845 participants of the 33 Communities Chinese Health Study and obesity (BMI ≥28 kg/m2) was defined according to the Working Group on Obesity in China. The Global Radiance Calibrated Nighttime Lights data were used to estimate participants' LAN exposure. The mixed-effect regression models examined the LAN-BMI and LAN-obesity association. We found that higher LAN exposure was significantly associated with greater BMI and higher risk of obesity. Changes of BMI and the odds ratios (ORs) of obesity and 95% confidence intervals (CIs) for 2nd, 3rd, and 4th against the 1st quartile of LAN exposure were 0.363 (0.208, 0.519), 0.364 (0.211, 0.516) and 0.217 (0.051, 0.383); 1.228 (1.099, 1.371), 1.356 (1.196, 1.538) and 1.269 (1.124, 1.433), respectively. Age and regular exercise showed significant modification effects on the LAN-obesity association.

Feeding during the resting phase causes gastrointestinal tract dysfunction and desynchronization of metabolic and neuronal rhythms in rats

BACKGROUND

Disrupted circadian rhythms may result from a misalignment between the environmental cycles (due to shift work, sleep restriction, feeding at an unusual time of day) and endogenous rhythms or by physiological aging. Among the numerous adverse effects, disrupted rhythms affect the brain-gut axis, contributing to the pathogenesis of several diseases in the gastrointestinal tract, for example, abdominal pain, constipation, gastric dyspepsia, inflammatory bowel disease, irritable bowel syndrome, and others.

METHODS

This study evaluated the rat gastric emptying, gastrointestinal motility, a clock gene, gut hormones, and the neuron activity on the nucleus of tractus solitarius (NTS), area postrema (AP), and the dorsal motor nucleus of the vagus (DMV) in rats with restricted food access to the rest phase for 4 weeks.

KEY RESULTS

Our results show that food restricted to the rest light period disturbed the expression pattern of a series of transcripts, including metabolic and circadian regulation. Also, the secretion of gastrointestinal hormones, gastric emptying, intestinal motility, and NTS, AP, and DMV activity were altered.

CONCLUSIONS & INFERENCES

These data indicate the importance of the time of the day food is ingested on the regulation of energy balance and the endocrine activity of the stomach and small intestine, emphasizing the importance of food as a powerful circadian synchronizer and an essential factor for the triggering of gastrointestinal diseases and metabolic problems. These findings offer a novel clue regarding the obesity-promoting effect attributed to feeding time and open the possibility of treating this and other intestinal disorders.

Minor Changes in Daily Rhythms Induced by a Skeleton Photoperiod Are Associated with Increased Adiposity and Glucose Intolerance

Eating during the rest phase is associated with metabolic syndrome, proposed to result from a conflict between food consumption and the energy-saving state imposed by the circadian system. However, in nocturnal rodents, eating during the rest phase (day-feeding, DF) also implies food intake during light exposure. To investigate whether light exposure contributes to DF-induced metabolic impairments, animals receive food during the subjective day without light. A skeleton photoperiod (SP) is used to entrain rats to a 12:12 cycle with two short light pulses framing the subjective day. DF-induced adiposity is prevented by SP, suggesting that the conflict between light and feeding stimulates fat accumulation. However, all animals under SP conditions develop glucose intolerance regardless of their feeding schedule. Moreover, animals under SP with ad libitum or night-feeding have increased adiposity. SP animals show a delayed onset of the daily rise in body temperature and energy expenditure and shorter duration of nighttime activity, which may contribute to the metabolic disturbances. These data emphasize that metabolic homeostasis can only be achieved when all daily cycling variables are synchronized. Even small shifts in the alignment of different metabolic rhythms, such as those induced by SP, may predispose individuals to metabolic disease.

The concept of "metabolic jet lag" in the pathophysiology of bipolar disorder: implications for research and clinical care

Bipolar disorder (BD) is a potentially chronic mental disorder marked by recurrent depressive and manic episodes, circadian rhythm disruption, and changes in energetic metabolism. "Metabolic jet lag" refers to a state of shift in circadian patterns of energy homeostasis, affecting neuroendocrine, immune, and adipose tissue function, expressed through behavioral changes such as irregularities in sleep and appetite. Risk factors include genetic variation, mitochondrial dysfunction, lifestyle factors, poor gut microbiome health and abnormalities in hunger, satiety, and hedonistic function. Evidence suggests metabolic jet lag is a core component of BD pathophysiology, as individuals with BD frequently exhibit irregular eating rhythms and circadian desynchronization of their energetic metabolism, which is associated with unfavorable clinical outcomes. Although current diagnostic criteria lack any assessment of eating rhythms, technological advancements including mobile phone applications and ecological momentary assessment allow for the reliable tracking of biological rhythms. Overall, methodological refinement of metabolic jet lag assessment will increase knowledge in this field and stimulate the development of interventions targeting metabolic rhythms, such as time-restricted eating.

Timing Matters: The Interplay between Early Mealtime, Circadian Rhythms, Gene Expression, Circadian Hormones, and Metabolism-A Narrative Review

Achieving synchronization between the central and peripheral body clocks is essential for ensuring optimal metabolic function. Meal timing is an emerging field of research that investigates the influence of eating patterns on our circadian rhythm, metabolism, and overall health. This narrative review examines the relationship between meal timing, circadian rhythm, clock genes, circadian hormones, and metabolic function. It analyzes the existing literature and experimental data to explore the connection between mealtime, circadian rhythms, and metabolic processes. The available evidence highlights the importance of aligning mealtime with the body's natural rhythms to promote metabolic health and prevent metabolic disorders. Specifically, studies show that consuming meals later in the day is associated with an elevated prevalence of metabolic disorders, while early time-restricted eating, such as having an early breakfast and an earlier dinner, improves levels of glucose in the blood and substrate oxidation. Circadian hormones, including cortisol and melatonin, interact with mealtimes and play vital roles in regulating metabolic processes. Cortisol, aligned with dawn in diurnal mammals, activates energy reserves, stimulates appetite, influences clock gene expression, and synchronizes peripheral clocks. Consuming meals during periods of elevated melatonin levels, specifically during the circadian night, has been correlated with potential implications for glucose tolerance. Understanding the mechanisms of central and peripheral clock synchronization, including genetics, interactions with chronotype, sleep duration, and hormonal changes, provides valuable insights for optimizing dietary strategies and timing. This knowledge contributes to improved overall health and well-being by aligning mealtime with the body's natural circadian rhythm.

Time-restricted feeding affects colonic nutrient substrates and modulates the diurnal fluctuation of microbiota in pigs

Introduction

Studies demonstrate that time-restricted feeding (TRF) can regulate gut microbiota composition. However, it is unclear whether TRF could affect the gut microbial rhythmicity in growing pigs. Therefore, the present study aimed to explore the effects of TRF on the dynamic fluctuation of the gut microbiota.

Methods

A total of 10 healthy growing pigs equipped with T cannula were employed. Pigs were randomly allotted to the free access (FA) and the TRF groups with 5 replicates (1 pig/replicates). Pigs in the FA group were fed free access during the whole experimental period, whereas pigs in the TRF group were fed free access three times per day within limited times (7:00-8:00, 12:00-13:00, 17:00-18:00). The experiment lasted for 15 days, at 06:00 a.m. of the day 16, colonic digesta were collected at a 6-h interval for consecutive 24 h marked as T06 (06:00), T12 (12:00), T18 (18:00), T24 (24:00), T30 (06:00), respectively.

Results

Results showed that TRF altered the distribution of feed intake without changing the total feed intake within a day (p = 0.870). TRF decreased the overall concentration of colonic cellulose and altered their oscillating patterns. All alpha-diversity indexes of different time points showed significant differences regardless of feeding pattern with a trough at T18 or T24. TRF shifted the trough of the alpha-diversity index Simpson and Invsimpson. TRF lost the rhythmicity of Prevotellaceae, Ruminococcaceae, Bacteroidales_S24-7_group, and Peptococcaceae and gained the rhythmicity of Pasteurellaceae, Clostridiaceae_1, Veillonellaceae, and Peptostreptococcaceae. Also, TRF altered the interaction pattern by increasing the microbes involved in the co-occurrence network and their crosstalk, especially at T24. Interestingly, the microbial variation at T24 could largely explained by colonic substrates starch (R² = 0.369; p = 0.001), cellulose (R² = 0.235; p = 0.009) and NH4-N (R² = 0.489; p = 0.001).

Conclusion

In conclusion, TRF has changed the concentrates of cellulose and the relative abundance of specific microbes and certain microbial metabolites. In addition, TRF has more powerful effects on the fluctuation modes of these nutrient substrates, microbes, and metabolites by shifting their peaks or troughs. This knowledge facilitates the development of precision regulation targeting gut microbial rhythmicity.

Human glucose rhythms and subjective hunger anticipate meal timing

Circadian rhythms, metabolism, and nutrition are closely linked.¹ Timing of a three-meal daily feeding pattern synchronizes some human circadian rhythms.² Despite animal data showing anticipation of food availability, linked to a food-entrainable oscillator,³ it is unknown whether human physiology predicts mealtimes and restricted food availability. In a controlled laboratory protocol, we tested the hypothesis that the human circadian system anticipates large meals. Twenty-four male participants undertook an 8-day laboratory study, with strict sleep-wake schedules, light-dark schedules, and food intake. For 6 days, participants consumed either hourly small meals throughout the waking period or two large daily meals (7.5 and 14.5 h after wake-up). All participants then undertook a 37-h constant routine. Interstitial glucose was measured every 15 min throughout the protocol. Hunger was assessed hourly during waking periods. Saliva melatonin was measured in the constant routine. During the 6-day feeding pattern, both groups exhibited increasing glucose concentration early each morning. In the small meal group, glucose concentrations continued to increase across the day. However, in the large meal group, glucose concentrations decreased from 2 h after waking until the first meal. Average 24-h glucose concentration did not differ between groups. In the constant routine, there was no difference in melatonin onset between groups, but antiphasic glucose rhythms were observed, with low glucose at the time of previous meals in the large meal group. Moreover, in the large meal group, constant routine hunger scores increased before the predicted meal times. These data support the existence of human food anticipation.

Circadian clock and temporal meal pattern

The central circadian clock in the brain controls the time-of-the-day variations in acute meal responses, with a low glycemic response but a high satiety/thermogenic response to meals consumed at waking compared to other time points. Consistently, studies show that consuming a significant proportion of calories, particularly carbohydrates, in breakfast is beneficial for the chronic management of obesity and its associated metabolic syndrome, compared to consuming identical meals at dinner. Conversely, breakfast skipping or/and late dinner can have unfavorable metabolic outcomes. It remains controversial how meal frequency affects metabolic health. In contrast, irregular meals, especially irregular breakfasts, show consistent adverse metabolic consequences. Time-restricted feeding (TRF), with all calories consumed within less than 12-h per day, can improve metabolism and extend lifespan. A major component of TRF in humans is caloric restriction, which contributes significantly to the beneficial effects of TRF in humans. By comparison, TRF effects in rodents can be independent of caloric restriction and show day/night phase specificity. TRF could alleviate metabolic abnormalities due to circadian disruption, but its effects appear independent of the circadian clock in rodents. Understanding neuroendocrine mechanisms underlying clock-mediated metabolic regulation will shed light on the metabolic effects of temporal meal patterns.

Finding balance: understanding the energetics of time-restricted feeding in mice

Over the course of mammalian evolution, the ability to store energy likely conferred a survival advantage when food became scarce. A long-term increase in energy storage results from an imbalance between energy intake and energy expenditure, two tightly regulated parameters that generally balance out to maintain a fairly stable body weight. Understanding the molecular determinants of this feat likely holds the key to new therapeutic development to manage obesity and associated metabolic dysfunctions. Time-restricted feeding (TRF), a dietary intervention that limits feeding to the active phase, can prevent and treat obesity and metabolic dysfunction in rodents fed a high-fat diet, likely by exerting effects on energetic balance. Even when body weight is lower in mice on active-phase TRF, food intake is generally isocaloric as compared with ad libitum fed controls. This discrepancy between body weight and energy intake led to the hypothesis that energy expenditure is increased during TRF. However, at present, there is no consensus in the literature as to how TRF affects energy expenditure and energy balance as a whole, and the mechanisms behind metabolic adaptation under TRF are unknown. This review examines our current understanding of energy balance on TRF in rodents and provides a framework for future studies to evaluate the energetics of TRF and its molecular determinants.

Chronotype Differences in Body Composition, Dietary Intake and Eating Behavior Outcomes: A Scoping Systematic Review

The timing and nutritional composition of food intake are important zeitgebers for the biological clocks in humans. Thus, eating at an inappropriate time (e.g., during the night) may have a desynchronizing effect on the biological clocks and, in the long term, may result in adverse health outcomes (e.g., weight gain, obesity, and poor metabolic function). Being a very late or early chronotype not only determines preferred sleep and wake times but may also influence subsequent mealtimes, which may affect the circadian timing system. In recent years, an increased number of studies have examined the relation between chronotype and health outcomes, with a main focus on absolute food intake and metabolic markers and, to a lesser extent, on dietary intake distribution and eating behavior. Therefore, this review aimed to systematically determine whether chronotype indirectly affects eating behaviors, dietary intake (timing, choice, nutrients), and biomarkers leading to body composition outcomes in healthy adults. A systematic literature search on electronic databases (PubMed, CINAHL, MEDLINE, SCOPUS, Cochrane library) was performed (International Prospective Register of Systematic Reviews number: CRD42020219754). Only studies that included healthy adults (aged >18 y), classified according to chronotype and body composition profiles, using outcomes of dietary intake, eating behavior, and/or biomarkers, were considered. Of 4404 articles, 24 met the inclusion criteria. The results revealed that late [evening type (ET)] compared with early [morning type (MT)] chronotypes were more likely to be overweight/obese with poorer metabolic health. Both MT and ET had similar energy and macronutrient intakes, consuming food during their preferred sleep-wake timing: later for ET than MT. Most of the energy and macronutrient intakes were distributed toward nighttime for ET and exacerbated by unhealthy eating behaviors and unfavorable dietary intakes. These findings from our systematic review give further insight why higher rates of overweight/obesity and unhealthier metabolic biomarkers are more likely to occur in ET.

Sex differences in the association between dinner-bedtime interval and abdominal obesity: a large-scale cross-sectional study

PURPOSE

Dinner-bedtime interval was reported to be associated with general obesity. However, the association between dinner-bedtime interval and abdominal obesity is still unclear. This study was conducted to investigate the association of dinner-bedtime interval and abdominal obesity.

METHODS

A total of 7600 participants from Henan rural cohort study were included in this study. A standard questionnaire was used to obtain the time of dinner and sleep by the way of face-to-face interview. Sleep quality of each participant was evaluated by Pittsburgh Sleep Quality Index. Logistic regression and restricted cubic spline were used to assess the association between dinner-bedtime interval and abdominal obesity. Line regression was used to estimate the association between dinner-bedtime interval and lipid metabolism indexes. The mediation effect of sleep quality on the relationship between dinner-bedtime interval and abdominal obesity was evaluated.

RESULTS

In male, increased dinner-bedtime interval was associated with abdominal obesity risk (Adjusted OR: 1.084, 95% CI 1.009-1.164). Compared with participants with dinner-bedtime interval ≤ 2 h, those dinner-bedtime interval > 2 h had an elevated risk of abdominal obesity (Adjusted OR: 1.199, 95% CI 1.009-1.425). In addition, a positive linear dose-response relationship was detected between dinner-bedtime interval and abdominal obesity. Moreover, total cholesterol concentration increased by 0.047 mmol/L for each 1-h increase in dinner-bedtime interval (P = 0.019). In addition, sleep quality mediated 11.45% of the relationship between dinner-bedtime interval and abdominal obesity (adjusted mediation effect: - 0.010, 95% CI - 0.019 to - 0.003). But in female, these associations were not significant.

CONCLUSION

It is suggested that increased dinner-bedtime interval was related to a higher risk of abdominal obesity in rural China and this association was differed by sex.

LEVEL OF EVIDENCE

Level V: cross-sectional descriptive study.

Different levels of circadian (de)synchrony -- where does it hurt?

A network of cellular timers ensures the maintenance of homeostasis by temporal modulation of physiological processes across the day. These so-called circadian clocks are synchronized to geophysical time by external time cues (or zeitgebers). In modern societies, natural environmental cycles are disrupted by artificial lighting, around-the-clock availability of food or shift work. Such contradictory zeitgeber input promotes chronodisruption, i.e., the perturbation of internal circadian rhythms, resulting in adverse health outcomes. While this phenomenon is well described, it is still poorly understood at which level of organization perturbed rhythms impact on health and wellbeing. In this review, we discuss different levels of chronodisruption and what is known about their health effects. We summarize the results of disrupted phase coherence between external and internal time vs. misalignment of tissue clocks amongst each other, i.e., internal desynchrony. Last, phase incoherence can also occur at the tissue level itself. Here, alterations in phase coordination can emerge between cellular clocks of the same tissue or between different clock genes within the single cell. A better understanding of the mechanisms of circadian misalignment and its effects on physiology will help to find effective tools to prevent or treat disorders arising from modern-day chronodisruptive environments.

The impact of eating behaviors during COVID-19 in health-care workers: A conditional process analysis of eating, affective disorders, and PTSD

Objective

The incidence of post-traumatic stress disorder (PTSD) increased among healthcare workers (HCWs) during the outbreak of COVID-19. The purpose of this study was to examine the relationship between eating behavior and PTSD, considering the mediation effect of anxiety, depression and sleep.

Methods

A total of 101 HCWs completed a survey. The Food-Frequency Questionnaires (FFQ) were used to evaluate the diet. A special survey was conducted on the eating time of each shift mode. The PTSD Checklist-Civilian Version (PCL-C), Self-Rating Anxiety Scale (SAS), Self-Rating Depression Scale (SDS), Pittsburgh Sleep Quality Index (PSQI), and Morning-Evening Questionnaire (MEQ) were utilized to assess clinical symptoms.

Results

There was a statistically significant correlation between the night shift eat midpoint (NEMP) and PTSD symptoms, anxiety and depression as significant mediators. The last meal jet lag between night shift and day shift (NDLM) was related to PTSD symptoms significantly, and sleep and anxiety were significant mediators. The relationship between animal-based protein pattern and PTSD symptoms was statistically significant, and anxiety was the significant mediator.

Conclusions

The earlier the HCWs eat in the night shift, the lighter the symptoms of PTSD. This is mediated by improving anxiety, depression and sleep disorder. Furthermore, the consumption of animal protein could reduce symptoms of PTSD by improving anxiety.

Late isocaloric eating increases hunger, decreases energy expenditure, and modifies metabolic pathways in adults with overweight and obesity

Late eating has been linked to obesity risk. It is unclear whether this is caused by changes in hunger and appetite, energy expenditure, or both, and whether molecular pathways in adipose tissues are involved. Therefore, we conducted a randomized, controlled, crossover trial (ClinicalTrials.gov NCT02298790) to determine the effects of late versus early eating while rigorously controlling for nutrient intake, physical activity, sleep, and light exposure. Late eating increased hunger (p < 0.0001) and altered appetite-regulating hormones, increasing waketime and 24-h ghrelin:leptin ratio (p < 0.0001 and p = 0.006, respectively). Furthermore, late eating decreased waketime energy expenditure (p = 0.002) and 24-h core body temperature (p = 0.019). Adipose tissue gene expression analyses showed that late eating altered pathways involved in lipid metabolism, e.g., p38 MAPK signaling, TGF-β signaling, modulation of receptor tyrosine kinases, and autophagy, in a direction consistent with decreased lipolysis/increased adipogenesis. These findings show converging mechanisms by which late eating may result in positive energy balance and increased obesity risk.

Complex physiology and clinical implications of time-restricted eating

Time-restricted eating (TRE) is a dietary intervention that limits food consumption to a specific time window each day. The effect of TRE on body weight and physiological functions has been extensively studied in rodent models, which have shown considerable therapeutic effects of TRE and important interactions among time of eating, circadian biology, and metabolic homeostasis. In contrast, it is difficult to make firm conclusions regarding the effect of TRE in people because of the heterogeneity in results, TRE regimens, and study populations. In this review, we 1) provide a background of the history of meal consumption in people and the normal physiology of eating and fasting; 2) discuss the interaction between circadian molecular metabolism and TRE; 3) integrate the results of preclinical and clinical studies that evaluated the effects of TRE on body weight and physiological functions; 4) summarize other time-related dietary interventions that have been studied in people; and 4) identify current gaps in knowledge and provide a framework for future research directions.

Timed restricted feeding cycles drive daily rhythms in female rats maintained in constant light but only partially restore the estrous cycle

Light at night is an emergent problem for modern society. Rodents exposed to light at night develop a loss of circadian rhythms, which leads to increased adiposity, altered immune response, and increased growth of tumors. In female rats, constant light (LL) eliminates the estrous cycle leading to a state of persistent estrus. The suprachiasmatic nucleus (SCN) drives circadian rhythms, and it interacts with the neuroendocrine network necessary for reproductive function. Timed restricted feeding (RF) exerts a powerful entraining influence on the circadian system, and it can influence the SCN activity and can restore rhythmicity or accelerate re-entrainment in experimental conditions of shift work or jet lag. The present study explored RF in female rats exposed to LL, with the hypothesis that this cyclic condition can rescue or prevent the loss of daily rhythms and benefit the expression of the estrous cycle. Two different feeding schedules were explored: 1. A 12-h food/12-h fasting schedule applied to arrhythmic rats after 3 weeks in LL, visualized as a rescue strategy (LL + RFR, 3 weeks), or applied simultaneously with the first day of LL as a preventive strategy (LL + RFP, 6 weeks). 2. A 12-h window of food intake with food given in four distributed pulses (every 3 h), applied after 3 weeks in LL, as a rescue strategy (LL + PR, 3 weeks) or applied simultaneously with the first day of LL as a preventive strategy (LL + PP, 6 weeks). Here, we present evidence that scheduled feeding can drive daily rhythms of activity and temperature in rats exposed to LL. However, the protocol of distributed feeding pulses was more efficient to restore the day–night activity and core temperature as well as the c-Fos day–night change in the SCN. Likewise, the distributed feeding partially restored the estrous cycle and the ovary morphology under LL condition. Data here provided indicate that the 12-h feeding/12-h fasting window determines the rest-activity cycle and can benefit directly the circadian and reproductive function. Moreover, this effect is stronger when food is distributed along the 12 h of subjective night.

Circadian rhythms and pancreas physiology: A review

Type 2 diabetes mellitus, obesity and metabolic syndrome are becoming more prevalent worldwide and will present an increasingly challenging burden on healthcare systems. These interlinked metabolic abnormalities predispose affected individuals to a plethora of complications and comorbidities. Furthermore, diabetes is estimated by the World Health Organization to have caused 1.5 million deaths in 2019, with this figure projected to rise in coming years. This highlights the need for further research into the management of metabolic diseases and their complications. Studies on circadian rhythms, referring to physiological and behavioral changes which repeat approximately every 24 hours, may provide important insight into managing metabolic disease. Epidemiological studies show that populations who are at risk of circadian disruption such as night shift workers and regular long-haul flyers are also at an elevated risk of metabolic abnormalities such as insulin resistance and obesity. Aberrant expression of circadian genes appears to contribute to the dysregulation of metabolic functions such as insulin secretion, glucose homeostasis and energy expenditure. The potential clinical implications of these findings have been highlighted in animal studies and pilot studies in humans giving rise to the development of circadian interventions strategies including chronotherapy (time-specific therapy), time-restricted feeding, and circadian molecule stabilizers/analogues. Research into these areas will provide insights into the future of circadian medicine in metabolic diseases. In this review, we discuss the physiology of metabolism and the role of circadian timing in regulating these metabolic functions. Also, we review the clinical aspects of circadian physiology and the impact that ongoing and future research may have on the management of metabolic disease.

The Circadian Regulation of Nutrient Metabolism in Diet-Induced Obesity and Metabolic Disease

Obesity and other metabolic diseases are major public health issues that are particularly prevalent in industrialized societies where circadian rhythmicity is disturbed by shift work, jet lag, and/or social obligations. In mammals, daylight entrains the hypothalamic suprachiasmatic nucleus (SCN) to a ≈24 h cycle by initiating a transcription/translation feedback loop (TTFL) of molecular clock genes. The downstream impacts of the TTFL on clock-controlled genes allow the SCN to set the rhythm for the majority of physiological, metabolic, and behavioral processes. The TTFL, however, is ubiquitous and oscillates in tissues throughout the body. Tissues outside of the SCN are entrained to other signals, such as fed/fasting state, rather than light input. This system requires a considerable amount of biological flexibility as it functions to maintain homeostasis across varying conditions contained within a 24 h day. In the face of either circadian disruption (e.g., jet lag and shift work) or an obesity-induced decrease in metabolic flexibility, this finely tuned mechanism breaks down. Indeed, both human and rodent studies have found that obesity and metabolic disease develop when endogenous circadian pacing is at odds with the external cues. In the following review, we will delve into what is known on the circadian rhythmicity of nutrient metabolism and discuss obesity as a circadian disease.

Cyrcadian Rhythm, Mood, and Temporal Patterns of Eating Chocolate: A Scoping Review of Physiology, Findings, and Future Directions

This paper discusses the effect of chrononutrition on the regulation of circadian rhythms; in particular, that of chocolate on the resynchronization of the human internal biological central and peripheral clocks with the main external synchronizers, light–dark cycle and nutrition-fasting cycle. The desynchronization of internal clocks with external synchronizers, which is so frequent in our modern society due to the tight rhythms imposed by work, social life, and technology, has a negative impact on our psycho-physical performance, well-being, and health. Taking small amounts of chocolate, in the morning at breakfast at the onset of the active phase, helps speed up resynchronization time. The high flavonoid contents in chocolate promote cardioprotection, metabolic regulation, neuroprotection, and neuromodulation with direct actions on brain function, neurogenesis, angiogenesis, and mood. Although the mechanisms of action of chocolate compounds on brain function and mood as well as on the regulation of circadian rhythms have yet to be fully understood, data from the literature currently available seem to agree in suggesting that chocolate intake, in compliance with chrononutrition, could be a strategy to reduce the negative effects of desynchronization. This strategy appears to be easily implemented in different age groups to improve work ability and daily life.

Impact of Time-Restricted Feeding on Adaptation to a 6-Hour Delay Phase Shift or a 12-Hour Phase Shift in Mice

Nowadays, more and more people are suffering from circadian disruption. However, there is no well-accepted treatment. Recently, time-restricted feeding (TRF) was proposed as a potential non-drug intervention to alleviate jet lag in mice, especially in mice treated with a 6-h advanced phase shift. Here, we challenged C57BL/6 mice with a 6-h delay phase shift or a 12-h shift (day-night reversal) combined with 6- or 12-h TRF within the dark phase and found the beneficial effects of given TRF strategies in certain phase-shifting situations. Although behavioral fitness did not correlate well with health status, none of the TRF strategies we used deteriorated lipopolysaccharide-induced sepsis. These findings improve our understanding of the benefits of TRF for adaptation to circadian disruption.

Work Around the Clock: How Work Hours Induce Social Jetlag and Sleep Deficiency

A growing body of evidence has placed an increasing emphasis on how sleep affects health. Not only does insufficient sleep make one subjectively feel worse, but is associated with chronic diseases that are considered epidemics in industrialized nations. This is partly caused by the growing need for prolonged work and social schedules, exemplified by shift work, late-night weekends, and early morning work/school start times (social jetlag). Here, we consider fundamental relationships between the circadian clock and biologic processes and discuss how common practices, such as shift work and social jetlag, contribute to sleep disruption, circadian misalignment, and adverse health outcomes.

Misaligned feeding schedule elicits divergent circadian reorganizations in endo- and exocrine pancreas clocks

Misaligned feeding may lead to pancreatic insufficiency, however, whether and how it affects circadian clock in the exocrine pancreas is not known. We exposed rats to a reversed restricted feeding regimen (rRF) for 10 or 20 days and analyzed locomotor activity, daily profiles of hormone levels (insulin, glucagon, and corticosterone) in plasma, and clock gene expression in the liver and endocrine and exocrine pancreas. In addition, we monitored responses of the exocrine pancreatic clock in organotypic explants of mPer2Luc mice in real time to acetylcholine, insulin, and glucocorticoids. rRF phase-reversed the clock in the endocrine pancreas, similar to the clock in the liver, but completely abolished clock gene rhythmicity and significantly downregulated the expression of Cpb1 and Cel in the exocrine pancreas. rRF desynchronized the rhythms of plasma insulin and corticosterone. Daily profiles of their receptor expression differed in the two parts of the pancreas and responded differently to rRF. Additionally, the pancreatic exocrine clock responded differently to treatments with insulin and the glucocorticoid analog dexamethasone in vitro. Mathematical simulation confirmed that the long-term misalignment between these two hormonal signals, as occurred under rRF, may lead to dampening of the exocrine pancreatic clock. In summary, our data suggest that misaligned meals impair the clock in the exocrine part of the pancreas by uncoupling insulin and corticosterone rhythms. These findings suggest a new mechanism by which adverse dietary habits, often associated with shift work in humans, may impair the clock in the exocrine pancreas and potentially contribute to exocrine pancreatic insufficiency.

Lack of food intake during shift work alters the heart transcriptome and leads to cardiac tissue fibrosis and inflammation in rats

Background

Many epidemiological studies revealed that shift work is associated with an increased risk of a number of pathologies, including cardiovascular diseases. An experimental model of shift work in rats has additionally been shown to recapitulate aspects of metabolic disorders observed in human shift workers, including increased fat content and impaired glucose tolerance, and used to demonstrate that restricting food consumption outside working hours prevents shift work-associated obesity and metabolic disturbance. However, the way distinct shift work parameters, such as type of work, quantity, and duration, affect cardiovascular function and the underlying mechanisms, remains poorly understood. Here, we used the rat as a model to characterize the effects of shift work in the heart and determine whether they can be modulated by restricting food intake during the normal active phase.

Results

We show that experimental shift work reprograms the heart cycling transcriptome independently of food consumption. While phases of rhythmic gene expression are distributed across the 24-h day in control rats, they are clustered towards discrete times in shift workers. Additionally, preventing food intake during shift work affects the expression level of hundreds of genes in the heart, including genes encoding components of the extracellular matrix and inflammatory markers found in transcriptional signatures associated with pressure overload and cardiac hypertrophy. Consistent with this, the heart of shift worker rats not eating during work hours, but having access to food outside of shift work, exhibits increased collagen 1 deposition and displays increased infiltration by immune cells. While maintaining food access during shift work has less effects on gene expression, genes found in transcriptional signatures of cardiac hypertrophy remain affected, and the heart of shift worker rats exhibits fibrosis without inflammation.

Conclusions

Together, our findings unraveled differential effects of food consumption on remodeled transcriptional profiles of the heart in shift worker rats. They also provide insights into how shift work affects cardiac function and suggest that some interventions aiming at mitigating metabolic disorders in shift workers may have adverse effects on cardiovascular diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01256-9.

Changes in intestinal parameters and their association with dietary patterns in rotational shift workers

Circadian rhythm disturbances induced by rotating shift work contribute to development of metabolic disorders. However, their effects on intestinal parameters such as epithelial permeability and fecal short chain fatty acid (SCFA) levels have not been established yet. This study was planned to investigate the changes in intestinal integrity, fecal SCFA levels, gut microbiota and nutritional intake of rotational shift workers. The study was conducted on ten male rotational shift workers, 25-40 years old. Circadian rhythm disruption was assumed to have occurred after 14 days in the night shift. Dietary data which was obtained by using 24 h record for 7 days, physical activity data, anthropometric measurements, fecal and blood samples were collected during day and night shift. Changes in dietary consumption, anthropometric measurements, blood chemistry and intestinal epithelial permeability indicator according to day and night shifts were not significant (p > .05). Additionally, acetic, propionic and total SCFA were associated with the intestinal permeability biomarker in night shift, but not in day shift (p < .05). Consumption of dark green vegetables and beans and peas was positively associated with fecal isobutyric acid and fecal total SCFA concentration (r = 0.685, p = .029; r = 0.695, p = .026, respectively). The proportions of the genus including Blautia, Bifidobacterium, Dialister, and Ruminococcus gnavus group increased when individuals shifted to the night shift. Gut microbiota changes responding to circadian rhythm disruption became more prominent when consumed high sugar diet. So, changes have been observed in the gut microbiota of rotational shift workers, especially in individuals with certain dietary pattern. Moreover, in individuals with the circadian rhythm disruption SCFAs levels have been demonstrated to be associated with intestinal barrier integrity. A better understanding of the relation among fecal SCFAs, gut microbiota, intestinal epithelial permeability and circadian rhythm disruption is necessary for the development of new dietary strategies for gut health.

Induction of internal circadian desynchrony by misaligning zeitgebers

24-h rhythms in physiology and behaviour are orchestrated by an endogenous circadian clock system. In mammals, these clocks are hierarchically organized with a master pacemaker residing in the hypothalamic suprachiasmatic nucleus (SCN). External time signals-so-called zeitgebers-align internal with geophysical time. During shift work, zeitgeber input conflicting with internal time induces circadian desynchrony which, in turn, promotes metabolic and psychiatric disorders. However, little is known about how internal desynchrony is expressed at the molecular level under chronodisruptive environmental conditions. We here investigated the effects of zeitgeber misalignment on circadian molecular organisation by combining 28-h light-dark (LD-28) cycles with either 24-h (FF-24) or 28-h feeding-fasting (FF-28) regimes in mice. We found that FF cycles showed strong effects on peripheral clocks, while having little effect on centrally coordinated activity rhythms. Systemic, i.e., across-tissue internal circadian desynchrony was profoundly induced within four days in LD-28/FF-24, while phase coherence between tissue clocks was maintained to a higher degree under LD-28/FF-28 conditions. In contrast, temporal coordination of clock gene activity across tissues was reduced under LD-28/FF-28 conditions compared to LD-28/FF-24. These results indicate that timed food intake may improve internal synchrony under disruptive zeitgeber conditions but may, at the same time, weaken clock function at the tissue level.

Circadian effects on UV-induced damage and mutations

Skin cancer is the most diagnosed type of cancer in the United States, and while most of these malignancies are highly treatable, treatment costs still exceed $8 billion annually. Over the last 50 years, the annual incidence of skin cancer has steadily grown; therefore, understanding the environmental factors driving these types of cancer is a prominent research-focus. A causality between ultraviolet radiation (UVR) exposure and skin cancer is well-established, but exposure to UVR alone is not necessarily sufficient to induce carcinogenesis. The emerging field of circadian biology intersects strongly with the physiological systems of the mammalian body and introduces a unique opportunity for analyzing mechanisms of homeostatic disruption. The circadian clock refers to the approximate 24-hour cycle, in which protein levels of specific clock-controlled genes (CCGs) fluctuate based on the time of day. Though these CCGs are tissue specific, the skin has been observed to have a robust circadian clock that plays a role in its response to UVR exposure. This in-depth review will detail the mechanisms of the circadian clock and its role in cellular homeostasis. Next, the skin's response to UVR exposure and its induction of DNA damage and mutations will be covered - with an additional focus placed on how the circadian clock influences this response through nucleotide excision repair. Lastly, this review will discuss current models for studying UVR-induced skin lesions and perturbations of the circadian clock, as well as the impact of these factors on human health.

The Circadian Clock and Obesity

The modern way of life has dramatically affected our biological rhythms. Circadian rhythms, which are generated by an endogenous circadian clock, are observed in a large number of physiological functions including metabolism. Proper peripheral clock synchronization by different signals including appropriate feeding/fasting cycles is essential to coordinate and temporally gate metabolic processes. In this chapter, we emphasize the importance of nutrient sensing by peripheral clocks and highlight the major role of peripheral and central clock communication to locally regulate metabolic processes and ensure optimal energy storage and expenditure. As a consequence, changes in eating behavior and/or bedtime, as occurs upon shift work and jet lag, have direct consequences on metabolism and participate in the increasing prevalence of obesity and associated metabolic diseases such as type 2 diabetes and non-alcoholic fatty liver disease. In this setting, time-restricted feeding has been suggested as an efficient approach to ameliorate metabolic parameters and control body weight.

A novel PCOS rat model and an evaluation of its reproductive, metabolic, and behavioral phenotypes

Background

Although animal models of PCOS have been used in many studies, none of them can reproduce both the reproductive and metabolic phenotypes of PCOS. In addition, behavioral parameters have not been evaluated in PCOS animal models.

Purpose

We tried to produce an improved rat model of PCOS, and the reproductive, metabolic, and behavioral phenotypes of the model rats were evaluated.

Methods

Female rats were implanted with silicon tubes containing oil-dissolved dihydrotestosterone (Oil-DHT) as a new PCOS model. Their phenotypes were compared with those of conventional PCOS model rats (DHT), into which tubes containing crystalline DHT were implanted, and non-DHT-treated rats (control).

Results

Both the Oil-DHT and DHT rats showed greater body weight gain, food intake, and fat depot weight than the control rats. Furthermore, these groups showed fewer estrous stages and increased numbers of cystic follicles. The DHT rats exhibited lower ovarian and uterine weights than the control rats, whereas no such changes were observed in the Oil-DHT rats. The Oil-DHT and DHT rats showed less locomotor activity in the light phase than the control rats.

Conclusions

Our proposed PCOS model reproduced both the reproductive and metabolic phenotypes of PCOS and may have potential for PCOS research.

Daytime eating prevents internal circadian misalignment and glucose intolerance in night work

Night work increases diabetes risk. Misalignment between the central circadian “clock” and daily behaviors, typical in night workers, impairs glucose tolerance, likely due to internal misalignment between central and peripheral circadian rhythms. Whether appropriate circadian alignment of eating can prevent internal circadian misalignment and glucose intolerance is unknown. In a 14-day circadian paradigm, we assessed glycemic control during simulated night work with either nighttime or daytime eating. Assessment of central (body temperature) and peripheral (glucose and insulin) endogenous circadian rhythms happened during constant routine protocols before and after simulated night work. Nighttime eating led to misalignment between central and peripheral (glucose) endogenous circadian rhythms and impaired glucose tolerance, whereas restricting meals to daytime prevented it. These findings offer a behavioral approach to preventing glucose intolerance in shift workers.

Chronobiology and Metabolism: Is Ketogenic Diet Able to Influence Circadian Rhythm?

Circadian rhythms underpin most physiological processes, including energy metabolism. The core circadian clock consists of a transcription-translation negative feedback loop, and is synchronized to light-dark cycles by virtue of light input from the retina, to the central clock in the suprachiasmatic nucleus in the hypothalamus. All cells in the body have circadian oscillators which are entrained to the central clock by neural and humoral signals. In addition to light entrainment of the central clock in the brain, it now emerges that other stimuli can drive circadian clock function in peripheral tissues, the major one being food. This can then drive the liver clock to be misaligned with the central brain clock, a situation of internal misalignment with metabolic disease consequences. Such misalignment is prevalent, with shift workers making up 20% of the working population. The effects of diet composition on the clock are not completely clarified yet. High-fat diet and fasting influence circadian expression of clock genes, inducing phase-advance and phase-delay in animal models. Ketogenic diet (KD) is able to induce a metabolic switch from carbohydrate to fatty acid oxidation, miming a fasting state. In recent years, some animal studies have been conducted to investigate the ability of the KD to modify circadian gene expression, and demonstrated that the KD alters circadian rhythm and induces a rearrangement of metabolic gene expression. These findings may lead to new approaches to obesity and metabolic pathologies treatment.

New integrative approaches to discovery of pathophysiological mechanisms triggered by night shift work

Synchronization to periodic cues such as food/water availability and light/dark cycles is crucial for living organisms' homeostasis. Both factors have been heavily influenced by human activity, with artificial light at night (ALAN) being an evolutionary challenge imposed over roughly the last century. Evidence from studies in humans and animal models shows that overt circadian misalignment, such as that imposed to about 20% of the workforce by night shift work (NSW), negatively impinges on the internal temporal order of endocrinology, physiology, metabolism, and behavior. Moreover, NSW is often associated to mistimed feeding, with both unnatural behaviors being known to increase the risk of chronic diseases, such as eating disorders, overweight, obesity, cardiovascular, metabolic (particularly type 2 diabetes mellitus) and gastrointestinal disorders, some types of cancer, as well as mental disease including sleep disturbances, cognitive disorders, and depression. Regarding deleterious effects of ALAN on reproduction, increased risk of miscarriage, preterm delivery and low birth weight have been reported in shift-worker women. These mounting lines of evidence prompt further efforts to advance our understanding of the effects of long-term NSW on health. Emerging data suggest that NSW with or without mistimed feeding modify gene expression and functional readouts in different tissues/organs, which seem to translate into persistent cardiometabolic and endocrine dysfunction. However, this research avenue still faces multiple challenges, such as functional characterization of new experimental models more closely resembling human long-term NSW and mistimed feeding in males versus females; studying further target organs; identifying molecular changes by means of deep multi-omics analyses; and exploring biomarkers of NSW with translational medicine potential. Using high-throughput and systems biology is a relatively new approach to study NSW, aimed to generate experiments addressing new biological factors, pathways, and mechanisms, going beyond the boundaries of the circadian clock molecular machinery.

Unrestrained eating behavior and risk of mortality: A prospective cohort study

BACKGROUND & AIMS

Unrestrained eating behavior has been thought to be a proxy for diet frequency, timing, and caloric intake. We investigated the association of unrestrained eating with mortality risk in the Nurses' Health Study prospectively.

METHODS

During follow-up (1994-2016), 21,953 deaths were documented among 63,999 eligible participants in analyses of eating anything at any time, 22,120 deaths were documented among 65,839 participants in analyses of no concern with figure change. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated using Cox proportional hazards models.

RESULTS

Eating anything at any time was associated with an increased mortality from cancer (overall HR, 95%CI: 1.07, 1.00-1.13; driven by gastrointestinal tract cancer: 1.30, 1.10-1.54) and respiratory disease (1.16, 1.05-1.29), and decreased cardiovascular disease-specific mortality (0.92, 0.86-0.99), compared to those without this behavior; however, no association was observed between this behavior and all-cause mortality (1.02, 0.99-1.05). Women who reported having no concern with figure change experienced higher risk of mortality from all-cause (1.08, 1.05-1.11), cancer (1.08, 1.02-1.14), and respiratory disease (1.18, 1.08-1.30), compared to those not reporting this behavior. Their combined effect was associated with a higher all-cause (1.09, 1.04-1.14), cancer-specific (overall: 1.18, 1.09-1.28; gastrointestinal tract cancer: 1.36, 1.08-1.71; lung cancer: 1.09; 1.04-1.14), and respiratory disease-specific (1.30, 1.13-1.50) mortality, and was inversely associated with cardiovascular disease-specific mortality (0.88, 0.80-0.98), compared to those exhibiting the opposite.

CONCLUSIONS

Unrestrained eating was associated with increased risk of all-cause, cancer-specific (particularly for gastrointestinal tract cancer and lung cancer), and respiratory disease-specific mortality, and decreased risk of cardiovascular disease-specific mortality.

Social Jetlag Is Associated With Impaired Metabolic Control During a 1-Year Follow-Up

Previous studies have identified social jetlag (SJL) as a risk factor for non-communicable chronic diseases (NCCDs), but its association with metabolic control over time is unclear in the literature. Therefore, we examined the influence of SJL on metabolic parameters and blood pressure (BP) in patients with NCCDs over a 1-year follow-up. This retrospective, longitudinal study included 625 individuals (age: 56.0 +12.0 years; 76% female) with NCCDs [type 2 diabetes mellitus (TD2), systemic arterial hypertension (SHA), obesity, or dyslipidemia]. SJL was calculated based on the absolute difference between mid-sleep time on weekends and weekdays. Current metabolic parameters and BP of the patients were compared with data from a year prior. Generalized estimating equations (GEE) and multiple linear regression analyses were used to examine the association among SJL, metabolic parameters, and BP. Multiple linear regression analyses adjusted for confounders showed that SJL was positively associated with the delta difference of fasting glucose (β = 0.11, p = 0.02) and triglyceride levels (β = 0.09, p = 0.04) among all subjects with NCCDs, and with fasting glucose (β = 0.30, p = 0.0001) and triglyceride levels (β = 0.22, p = 0.01) in the TD2 group. GEE analysis demonstrated an isolated effect of SJL on diastolic BP. High SJL impaired clinical and metabolic control in individuals with NCCDs, leading to a worse profile after a 1-year follow-up, particularly among type II diabetics.

Circadian misalignment measured by social jetlag from early to late pregnancy and its association with nutritional status: a longitudinal study

A mismatch between circadian and social clocks leads to a circadian misalignment, which has been widely measured by social jetlag (SJL). There are several studies measuring SJL, but it has not been studied in pregnant women. Therefore, this study aimed to identify the occurrence of SJL throughout pregnancy and to verify whether there is an effect of pre-pregnancy body mass index (BMI) on SJL throughout pregnancy. The baseline of the present study was conducted with 205 1st trimester pregnant women of whom 100 were followed in their 2nd and 3rd trimester. SJL was calculated based on the absolute difference between mid-sleep time on workdays versus work-free days. The pre-pregnancy BMI and current BMI (kg/m²) were calculated. Linear regression and Generalised Estimating Equation (GEE) adjusted for confounders were used to determine the association between SJL and the gestational trimesters (time), and anthropometric variables. Most of the pregnant women (54.5%) presented SJL > 1 h in the first gestational trimester. We also found an isolated effect of the gestation trimester on the SJL mean. In this sense, pregnant women had a decrease in SJL from the second to the third trimester (1.33 ± 0.08 versus 1.12 ± 0.07, respectively; p = 0.012). GEE analyzes showed that pregnant women of a normal weight showed a decrease in SJL from the second to the third trimester (1.29 ± 0.11 and 0.93 ± 0.08, respectively, p = 0.032), but this was not found in the other groups of nutritional status (underweight, overweight and obesity). In addition, a positive association between SJL and pre-gestational BMI in the third trimester (β = 0.200, p = 0.046) was found. SJL is quite prevalent during the gestational period and excessive BMI both before and during pregnancy is associated with an increased risk of having SJL > 1 h in the third and second trimesters, respectively. In addition, pregnant women of normal weight—but not underweight or overweight—had decreased SJL from the second to the third trimester.