The Circadian Clock and Obesity

The Effectiveness of Time-Restricted Eating as an Intermittent Fasting Approach on Shift Workers' Glucose Metabolism: A Systematic Review and Meta-Analysis

Background/Objectives: Shift workers face higher risks of impaired glucose metabolism due to irregular eating habits and circadian misalignment. Time-restricted eating (TRE) could improve glucose metabolism by aligning food intake with the circadian clock, but its effectiveness remains unclear. Methods: Ten electronic databases (PubMed, EMBASE, Cochrane Library, CINAHL, PsycINFO, Scopus, Web of Science, ProQuest Dissertations and Theses, Science.gov, and ClinicalTrials.gov) were searched from journal inception to September 2024. Only randomized controlled trials (RCTs) involving shift workers were included. Meta-analyses with sensitivity analyses were conducted using a random-effects model to pool glucose metabolism and sleep outcomes, with heterogeneity and quality assessments performed. Results: Six RCTs were included. TRE demonstrated positive but non-significant effects on glucose metabolism outcomes: fasting blood glucose (weighted mean difference [WMD]: -0.02 mmol/L, 95% confidence interval [CI]: -0.13 to 0.10, I2 = 0%), fasting blood insulin (WMD: -5.77 pmol/L, 95% CI: -85.62 to 74.08, I2 = 92%), HOMA-IR (WMD: -0.50, 95% CI: -2.76 to 1.76, I2 = 82%), 2 h postprandial glucose (WMD: -0.65 mmol/L, 95% CI: -3.18 to 1.89, I2 = 86%), total sleep time (g = 0.07, 95% CI: -0.23 to 0.37, I2 = 0%), and sleep efficiency (g = -0.05, 95% CI: -0.63 to 0.53, I2 = 62%). Sensitivity analyses yielded similar findings, and overall certainty of evidence was rated 'very low'. Conclusions: While TRE shows potential for improving the glucose metabolism in shift workers, current evidence remains inconclusive due to small sample sizes and study limitations. Future research should prioritize well-powered TRE RCTs in shift workers that adhere to a 6-10 h eating window. Incorporating early-TRE schedules with sleep hygiene may optimize metabolic outcomes, with circadian biomarkers analyzed to better elucidate the mechanistic pathway implicated.

Circadian Disruption and the Risk of Developing Obesity

PURPOSE OF THE REVIEW

This review summarizes recent evidence for a role of the clock in adipose tissue physiology and the impact of circadian desynchrony on the development of obesity.

RECENT FINDINGS

Circadian disruptions due to shift work, late time eating and nighttime light exposure are associated with obesity and its metabolic and cardiovascular consequences. Studies in mice harboring tissue-specific gain/loss of function mutations in clock genes revealed that the circadian clock acts on multiple pathways to control adipogenesis, lipogenesis/lipolysis and thermogenesis. Time-restricted eating (TRE), aligning feeding with the active period to restore clock function, represents a promising strategy to curb obesity. While TRE has shown clear benefits, especially in participants at higher cardiometabolic risk, current studies are limited in size and duration. Larger, well-controlled studies are warranted to conclusively assess the effects of TRE in relation to the metabolic status and gender. Field studies in shift-workers, comparing permanent night shift versus rotating shifts, are also necessary to identify the optimal time window for TRE.

Association of Sleep Duration and Daytime Napping With Risk of Hyperuricemia: A Systematic Review and Meta-Analysis

BACKGROUND

Hyperuricemia (HUA), marked by elevated serum urate levels, is increasingly prevalent worldwide. The relationship between lifestyle factors such as sleep duration, daytime napping, and HUA risk remains unclear. Although some studies suggest that sleep variables, including short or long sleep durations and napping, may influence serum uric acid levels, results are inconsistent.

METHODS

A systematic review and meta-analysis was performed according to the PRISMA guidelines. Databases such as PubMed, Embase, Web of Science, and Cochrane Library were searched until February 2024. The data were extracted, and the quality of the study was assessed independently by two reviewers.

RESULTS

Ten studies involving a total of 231 978 participants were included. Short sleep duration was related to higher risk of HUA (odds ratio (OR) 1.10, 95% confidence interval (CI): 1.03-1.18), while long sleep duration had no significant effect (OR 0.98, 95% CI: 0.89-1.07). The risk of HUA and daytime napping was statistically significant(OR 1.34, 95% CI: 1.12-1.61).

CONCLUSIONS

Short sleep duration and prolonged daytime napping are associated with an increased risk of HUA. These findings suggest that sleep patterns should be considered in lifestyle interventions for HUA prevention. Further research is required to establish causal relationships.

Risk of Fat Mass- and Obesity-Associated Gene-Dependent Obesogenic Programming by Formula Feeding Compared to Breastfeeding

It is the purpose of this review to compare differences in postnatal epigenetic programming at the level of DNA and RNA methylation and later obesity risk between infants receiving artificial formula feeding (FF) in contrast to natural breastfeeding (BF). FF bears the risk of aberrant epigenetic programming at the level of DNA methylation and enhances the expression of the RNA demethylase fat mass- and obesity-associated gene (FTO), pointing to further deviations in the RNA methylome. Based on a literature search through Web of Science, Google Scholar, and PubMed databases concerning the dietary and epigenetic factors influencing FTO gene and FTO protein expression and FTO activity, FTO's impact on postnatal adipogenic programming was investigated. Accumulated translational evidence underscores that total protein intake as well as tryptophan, kynurenine, branched-chain amino acids, milk exosomal miRNAs, NADP, and NADPH are crucial regulators modifying FTO gene expression and FTO activity. Increased FTO-mTORC1-S6K1 signaling may epigenetically suppress the WNT/β-catenin pathway, enhancing adipocyte precursor cell proliferation and adipogenesis. Formula-induced FTO-dependent alterations of the N6-methyladenosine (m6A) RNA methylome may represent novel unfavorable molecular events in the postnatal development of adipogenesis and obesity, necessitating further investigations. BF provides physiological epigenetic DNA and RNA regulation, a compelling reason to rely on BF.

The Interconnection between Hepatic Insulin Resistance and Metabolic Dysfunction-Associated Steatotic Liver Disease-The Transition from an Adipocentric to Liver-Centric Approach

The central mechanism involved in the pathogenesis of MAFLD is insulin resistance with hyperinsulinemia, which stimulates triglyceride synthesis and accumulation in the liver. On the other side, triglyceride and free fatty acid accumulation in hepatocytes promotes insulin resistance via oxidative stress, endoplasmic reticulum stress, lipotoxicity, and the increased secretion of hepatokines. Cytokines and adipokines cause insulin resistance, thus promoting lipolysis in adipose tissue and ectopic fat deposition in the muscles and liver. Free fatty acids along with cytokines and adipokines contribute to insulin resistance in the liver via the activation of numerous signaling pathways. The secretion of hepatokines, hormone-like proteins, primarily by hepatocytes is disturbed and impairs signaling pathways, causing metabolic dysregulation in the liver. ER stress and unfolded protein response play significant roles in insulin resistance aggravation through the activation of apoptosis, inflammatory response, and insulin signaling impairment mediated via IRE1/PERK/ATF6 signaling pathways and the upregulation of SREBP 1c. Circadian rhythm derangement and biological clock desynchronization are related to metabolic disorders, insulin resistance, and NAFLD, suggesting clock genes as a potential target for new therapeutic strategies. This review aims to summarize the mechanisms of hepatic insulin resistance involved in NAFLD development and progression.

Circadian regulation of liver function: from molecular mechanisms to disease pathophysiology

A wide variety of liver functions are regulated daily by the liver circadian clock and via systemic circadian control by other organs and cells within the gastrointestinal tract as well as the microbiome and immune cells. Disruption of the circadian system, as occurs during jetlag, shift work or an unhealthy lifestyle, is implicated in several liver-related pathologies, ranging from metabolic diseases such as obesity, type 2 diabetes mellitus and nonalcoholic fatty liver disease to liver malignancies such as hepatocellular carcinoma. In this Review, we cover the molecular, cellular and organismal aspects of various liver pathologies from a circadian viewpoint, and in particular how circadian dysregulation has a role in the development and progression of these diseases. Finally, we discuss therapeutic and lifestyle interventions that carry health benefits through support of a functional circadian clock that acts in synchrony with the environment.