Insufficient sleep increases 24-hour energy expenditure by 4-5% (approximately 100 calories/day in young adults) but often leads to increased food intake and weight gain under ad libitum conditions. Circadian misalignment decreases 24-hour energy expenditure and alters appetite hormones (ghrelin, leptin, PYY), potentially promoting weight gain. Each hour of social jetlag increases the odds of metabolic syndrome by 30%.
The review presents a compelling case for the importance of sleep and circadian rhythms in metabolic health, synthesizing a substantial body of evidence from human studies. The overall quality of evidence is high, particularly in areas where controlled laboratory studies have been conducted, such as the impact of insufficient sleep on energy expenditure and appetite hormones. The review effectively addresses its research question by demonstrating a clear link between sleep disruption (both insufficient sleep and circadian misalignment) and increased obesity risk. The methodological rigor of the included studies is generally strong, with frequent use of gold-standard techniques like the constant routine protocol and whole-room calorimetry. However, the review also acknowledges the limitations of relying heavily on cross-sectional studies for investigating social jetlag and the impact of obesity on sleep, calling for more longitudinal research in these areas. The findings are significant and reliable for the field, providing valuable insights into the complex interplay between sleep, circadian rhythms, and metabolic health. The review's focus on human studies strengthens the translatability of the findings to clinical practice and public health interventions. The discussion of potential strategies to improve sleep, while comprehensive, could benefit from more specific and actionable recommendations. Overall, the review makes a valuable contribution to the field by highlighting the importance of sleep and circadian health in the context of the obesity pandemic and providing a strong foundation for future research and interventions.
The abstract effectively summarizes the main points of the review, including the prevalence of insufficient sleep and circadian misalignment, their impact on metabolic health, and the need for further research.
The abstract clearly states the focus of the review, which is on human studies, allowing readers to quickly understand the scope of the work.
This is a high-impact suggestion that improves the clarity and informativeness of the abstract. The abstract should explicitly mention the specific appetite hormones discussed in the review. This addition provides readers with a more complete understanding of the review's scope and key findings. This detailed information in the abstract helps readers quickly assess the relevance of the review to their interests.
Implementation: Add a brief mention of the specific appetite hormones (ghrelin, leptin, and peptide-YY) examined in the review. For example, 'This review discusses the impact of insufficient sleep and circadian misalignment in humans on appetite hormones, including ghrelin, leptin, and peptide-YY, energy expenditure, food intake and choice, and risk of obesity.'
This is a medium-impact suggestion that improves the precision and clarity of the abstract. The abstract mentions 'some potential strategies' but doesn't specify them. Briefly listing these strategies, such as physical activity, diet, and light exposure management, would make the abstract more informative and attract a wider readership interested in practical interventions.
Implementation: Include a concise list of the potential strategies mentioned. For example, 'Some potential strategies, including physical activity, dietary modifications, and light exposure management, to reduce the adverse effects of sleep disruption on metabolic health are provided.'
The introduction effectively establishes the context of the obesity pandemic and highlights the limitations of traditional risk factors in fully explaining its rise. This sets the stage for introducing insufficient sleep and circadian misalignment as novel contributors.
The introduction clearly states the review's focus on human studies, particularly young adult workers, where most mechanistic evidence exists. This defined scope helps readers understand the review's limitations and target audience.
The introduction provides a comprehensive overview of various sleep disruptors prevalent in modern society, including work patterns, screen time, substances, and emotional stressors. This thoroughness underscores the multifaceted nature of sleep disruption and its potential impact on metabolic health.
This is a high-impact suggestion as it would strengthen the rationale for the review by providing a more direct link between the historical context and the current obesity problem. While the introduction discusses historical sleep patterns, it doesn't explicitly connect these changes to the rise in obesity. This connection is crucial for establishing the review's relevance and justifying the focus on insufficient sleep and circadian misalignment. Elaborating on how the shift from pre-industrial sleep patterns to modern sleep habits correlates with the increasing prevalence of obesity would make the review's focus more compelling. This enhanced rationale would provide a stronger foundation for the review's arguments and improve its overall impact.
Implementation: Expand the discussion on historical sleep patterns to explicitly link the advent of electricity, 24/7 work culture, and increased screen time to the rise in obesity rates. Provide evidence or cite studies that demonstrate this correlation. For example, 'The shift from biphasic sleep in pre-industrial societies to the consolidated sleep pattern encouraged by electric lighting and 24/7 work schedules coincides with the dramatic increase in obesity rates observed in the 20th and 21st centuries [cite relevant studies]. This suggests a potential link between modern sleep disruption and metabolic health, warranting further investigation into the specific mechanisms involved.'
This is a medium-impact suggestion that would improve the introduction's clarity and organization. The introduction mentions the review's focus on appetite hormones, energy expenditure, food intake, and obesity risk. However, it would benefit from a more structured roadmap outlining the specific topics and their order of presentation within the review. A clear roadmap helps readers navigate the review and anticipate the flow of information. This improved structure enhances reader comprehension and makes the review more accessible.
Implementation: Add a concise roadmap at the end of the introduction, briefly outlining the structure of the review. For example, 'This review will first examine the impact of insufficient sleep and circadian misalignment on appetite hormones, followed by an analysis of their effects on energy expenditure, food intake and choice, and finally, their contribution to obesity risk. We will also discuss the impact of obesity on sleep and potential strategies for mitigating these adverse effects.'
The section effectively connects sleep and circadian disruption to energy regulation by focusing on 24-hour patterns of energy expenditure and key appetite hormones. This approach provides a more holistic view of energy balance than simply looking at isolated measurements.
This is a high-impact suggestion that would strengthen the section's discussion of GLP-1 and pancreatic polypeptide. The section briefly mentions these hormones but notes limited data availability. Expanding this discussion to include the potential roles of these hormones in sleep-related metabolic changes, even in the absence of robust data, would provide a more complete picture of hormonal influences on energy balance. This would also highlight areas for future research.
Implementation: Expand the discussion on GLP-1 and pancreatic polypeptide to include their potential roles in sleep-related metabolic changes, even if data are limited. Discuss potential mechanisms and highlight the need for further research to explore these relationships. For example, 'While data on GLP-1 and pancreatic polypeptide in the context of sleep disruption are limited, these hormones may play important roles in mediating the metabolic effects of insufficient sleep and circadian misalignment. GLP-1, for instance, is known to influence glucose homeostasis and satiety, and its diurnal rhythm may be affected by sleep patterns. Similarly, pancreatic polypeptide, which inhibits food intake, may also exhibit circadian variations that are sensitive to sleep disruption. Further research is needed to elucidate the specific roles of these hormones in sleep-related metabolic changes.'
This is a medium-impact suggestion that would improve the clarity and organization of the section. The section jumps between discussing energy expenditure and appetite hormones without a clear structure. Creating distinct subsections for each topic would enhance readability and allow for a more focused discussion of each factor's role in sleep-related metabolic changes.
Implementation: Divide the section into distinct subsections: one focusing on energy expenditure and the other on appetite hormones. Within each subsection, organize the information logically, starting with 24-hour variations, followed by the impact of insufficient sleep and circadian misalignment. This clear structure will improve the flow of information and make it easier for readers to follow the arguments.
Fig. 1. Energy expenditure in healthy adults is influenced by both sleep and circadian processes.
Fig. 2. The appetite-stimulating hormone ghrelin and the satiety hormones leptin and PYY are affected by energy intake, sleep and circadian rhythm in healthy adults.
The section effectively synthesizes findings from various studies to present a comprehensive overview of how insufficient sleep impacts energy expenditure, appetite hormones (ghrelin, leptin, PYY), and subsequent hunger and food intake. The discussion incorporates both controlled and uncontrolled energy intake conditions, providing a nuanced understanding of the complex interplay between sleep, energy balance, and appetite regulation.
This is a high-impact suggestion that would significantly enhance the section's contribution to the field by addressing a critical gap in the current literature. The section acknowledges the mixed findings on the impact of insufficient sleep on gut hormones like GLP-1 and pancreatic polypeptide, attributing these inconsistencies to potential sex or context dependencies. However, it stops short of exploring the underlying mechanisms that might explain these variations. A deeper dive into these potential mechanisms, even if speculative, would stimulate further research and provide a more complete understanding of the hormonal regulation of appetite in the context of sleep disruption. This enhanced discussion belongs in this section as it directly addresses the core topic of the section, which is the impact of insufficient sleep on appetite and energy balance. By exploring potential mechanisms, the review would move beyond simply reporting disparate findings and offer valuable insights into the complex interplay between sleep, gut hormones, and metabolic health. This would strengthen the review's contribution to the field and provide a more valuable resource for researchers and clinicians alike. Ultimately, incorporating a discussion of potential mechanisms underlying the observed variations in gut hormone responses to insufficient sleep would significantly enhance the section's scientific value and stimulate future research in this critical area.
Implementation: Expand the discussion on GLP-1 and pancreatic polypeptide to include a thorough exploration of potential mechanisms underlying the sex- and context-dependent effects of insufficient sleep on these hormones. Consider factors such as sex hormones, stress responses, meal timing, and macronutrient composition. For example, 'The observed sex differences in GLP-1 response to sleep restriction may be mediated by the interplay between sex hormones and sleep-related changes in cortisol or growth hormone secretion. Additionally, the context of energy balance (controlled vs. ad libitum) may influence GLP-1 secretion through its effects on glucose homeostasis and insulin sensitivity. Further research is needed to disentangle these complex interactions and elucidate the precise mechanisms by which insufficient sleep affects GLP-1 and pancreatic polypeptide secretion.'
This is a medium-impact suggestion that would improve the clarity and organization of the section. The current structure interweaves the discussion of energy expenditure and appetite hormones under different energy intake conditions (controlled and uncontrolled). While this approach highlights the interplay between these factors, it can also make it difficult for readers to follow the distinct effects of insufficient sleep on each aspect of energy balance. Separating these discussions into distinct subsections would enhance readability and allow for a more focused analysis of each component. This structural improvement is crucial for this section as it deals with complex interactions between multiple physiological variables. A clearer structure would facilitate reader comprehension and ensure that the key messages of the section are effectively conveyed. By presenting the information in a more organized manner, the review would become a more accessible and valuable resource for readers interested in understanding the impact of insufficient sleep on metabolic health. Ultimately, creating distinct subsections for energy expenditure and appetite hormones under controlled and uncontrolled energy intake conditions would significantly improve the clarity and impact of this section.
Implementation: Reorganize the section into distinct subsections: 1. Increased Energy Expenditure, 2. Controlled Energy Intake (Appetite Hormones and Hunger), 3. Uncontrolled Energy Intake (Appetite Hormones and Energy Intake). This will allow for a more focused discussion of each aspect and improve the overall flow of information. For example, under 'Controlled Energy Intake,' discuss the changes in ghrelin, leptin, and PYY and their association with increased hunger. Under 'Uncontrolled Energy Intake,' discuss the paradoxical changes in these hormones despite increased energy intake and weight gain.
Fig. 3. Model of changes in appetite hormones, hunger and energy intake in response to insufficient sleep.
Fig. 4. Insufficient sleep affects energy intake and energy expenditure, which leads to a positive energy balance and the risk of weight gain.
The section effectively synthesizes a large body of evidence from human studies, demonstrating a clear understanding of the complex interplay between circadian misalignment, energy expenditure, appetite hormones, and food choices.
The section clearly defines circadian misalignment from a metabolic perspective, providing a specific framework for the subsequent discussion.
The section effectively connects the discussion of circadian misalignment to the previous section on insufficient sleep, highlighting the overlapping and distinct effects of these two forms of sleep disruption.
This is a high-impact suggestion that would strengthen the section's discussion of the mechanisms underlying the effects of circadian misalignment. While the section mentions internal circadian desynchrony, it doesn't fully explore its potential role in the metabolic consequences of circadian misalignment in humans. Expanding on this concept, even with limited human data, would provide a more complete mechanistic picture and highlight an important area for future research.
Implementation: Expand the discussion of internal circadian desynchrony to include its potential role in the metabolic consequences of circadian misalignment in humans. Discuss the limited available evidence and propose specific research questions to address this gap. For example, 'While data on internal circadian desynchrony in humans are limited, this phenomenon may play a crucial role in the metabolic dysregulation observed during circadian misalignment. Future research should investigate whether internal desynchrony between central and peripheral clocks contributes to altered energy expenditure, appetite hormone profiles, and food choices in shift workers and other individuals experiencing chronic circadian misalignment.'
This is a medium-impact suggestion that would improve the clarity and organization of the section. The section discusses several related but distinct concepts, such as energy expenditure, food intake, physical activity, and appetite hormones. Creating separate subsections for each of these topics would enhance readability and allow for a more focused discussion of each factor's role in the metabolic consequences of circadian misalignment.
Implementation: Divide the section into distinct subsections for each key aspect of circadian misalignment's impact on metabolism: 1. Energy Expenditure, 2. Food Intake, Physical Activity, and Food Timing, 3. Appetite Hormones. This will improve the flow of information and make it easier for readers to follow the complex interplay between these factors.
The section effectively summarizes the complex interplay between circadian misalignment and insufficient sleep, highlighting their combined impact on ghrelin, leptin, and PYY levels.
The section emphasizes the need for further research to understand the influence of combined sleep restriction and circadian misalignment on energy intake under ad libitum conditions, addressing a crucial gap in the current literature.
This is a high-impact suggestion that would significantly enhance the section's contribution to the field by providing a more nuanced understanding of the interaction between circadian misalignment and insufficient sleep. While the section acknowledges that both factors disturb sleep, it doesn't fully explore the potential synergistic or antagonistic effects of these combined disruptions. A deeper discussion of how these factors interact at a physiological level, including their impact on the circadian clock, sleep architecture, and metabolic processes, would strengthen the review's mechanistic insights and provide a more comprehensive understanding of their combined effects on metabolic health. This enhanced discussion belongs in this section as it directly addresses the core topic of combined effects. By exploring the potential interactions, the review would move beyond simply reporting the individual effects of each factor and offer valuable insights into their combined influence on metabolic health. This would strengthen the review's contribution to the field and provide a more valuable resource for researchers and clinicians alike. Ultimately, incorporating a discussion of the potential interactions between circadian misalignment and insufficient sleep would significantly enhance the section's scientific value and stimulate future research in this critical area.
Implementation: Expand the discussion of combined effects to include a thorough exploration of potential interactions between circadian misalignment and insufficient sleep. Discuss how these factors might synergistically or antagonistically influence the circadian clock, sleep architecture (e.g., sleep stages, sleep efficiency), and metabolic processes (e.g., glucose homeostasis, hormone secretion). For example, 'The combined effects of circadian misalignment and insufficient sleep may not be simply additive, but rather interactive. Circadian misalignment can disrupt sleep architecture, leading to reduced slow-wave sleep and increased sleep fragmentation, which can further exacerbate the metabolic consequences of insufficient sleep. Additionally, insufficient sleep may alter the sensitivity of the circadian clock to light-dark cues, potentially worsening the effects of circadian misalignment. Further research is needed to disentangle these complex interactions and elucidate the precise mechanisms by which combined circadian misalignment and insufficient sleep affect metabolic health.'
The section effectively summarizes the current literature on circadian misalignment and obesity risk, encompassing both major disruptions (e.g., shift work) and more minor, frequent misalignments (e.g., social jetlag). This breadth of coverage provides a comprehensive overview of the topic.
The section clearly articulates the limitations of cross-sectional study designs prevalent in social jetlag research, highlighting the need for more robust longitudinal studies to investigate causal relationships.
This is a high-impact suggestion that would strengthen the section's discussion of the mechanisms linking circadian misalignment to obesity risk. While the section mentions several associated factors (e.g., food choices, energy expenditure), it would benefit from a more explicit discussion of the underlying physiological pathways. This would provide a deeper understanding of how circadian misalignment translates into increased obesity risk.
Implementation: Expand the discussion of mechanisms to include specific physiological pathways linking circadian misalignment to obesity risk. For example, discuss the role of the circadian clock in regulating glucose metabolism, lipid metabolism, and inflammation. Additionally, explore the interplay between circadian misalignment, gut microbiome dysbiosis, and metabolic health. For instance, 'Circadian misalignment can disrupt the gut microbiome, leading to increased intestinal permeability and inflammation, which can contribute to insulin resistance and weight gain.'
This is a medium-impact suggestion that would enhance the section's practical relevance. While the section mentions social jetlag and other common misalignments, it doesn't offer specific recommendations for mitigating their effects. Providing actionable strategies for reducing these everyday misalignments would empower readers to improve their circadian health.
Implementation: Include actionable strategies for mitigating the effects of social jetlag and other common misalignments. For example, suggest maintaining a consistent sleep schedule even on weekends, gradually shifting sleep times during travel, and optimizing light exposure during the day and evening. For instance, 'Individuals experiencing social jetlag can minimize its impact by maintaining a consistent sleep-wake schedule seven days a week, even if it means slightly shorter sleep on weekends.'
Fig. 5. Circadian misalignment affects energy intake and appetite hormones, which potentially leads to a positive energy balance and the risk of weight gain.
The section effectively summarizes the current research on the bidirectional relationship between obesity and sleep, acknowledging the focus on sleep disorders while highlighting the gap in knowledge regarding the independent effects of obesity on sleep.
The section correctly identifies the limitations of self-reported sleep data and cross-sectional study designs, emphasizing the need for more rigorous methodologies to understand the complex relationship between obesity and sleep.
This is a high-impact suggestion that would significantly enhance the section's contribution to the field by providing a more nuanced understanding of the complex relationship between obesity and sleep. While the section mentions several physiological and behavioral factors, it lacks a structured framework for organizing and discussing these factors. A more systematic approach would improve clarity and guide future research.
Implementation: Reorganize the section to present the physiological and behavioral factors affecting sleep in obesity within a clear framework. For example, create distinct subsections for 1. Physiological Factors (e.g., adipose tissue distribution, inflammation, gut microbiome) and 2. Behavioral Factors (e.g., diet, physical activity). Within each subsection, discuss the specific mechanisms by which these factors influence sleep. For instance, under 'Physiological Factors,' explain how visceral adipose tissue can lead to increased inflammation and hormonal imbalances that disrupt sleep.
This is a medium-impact suggestion that would enhance the section's clinical relevance and provide valuable insights for healthcare professionals. While the section acknowledges the importance of sleep disorders in obesity, it doesn't discuss the potential implications of these findings for clinical practice. Addressing this gap would bridge the gap between research and practice and improve patient care.
Implementation: Include a brief discussion of the clinical implications of the findings presented in this section. For example, discuss how understanding the independent effects of obesity on sleep can inform the development of targeted interventions for weight management and sleep improvement in individuals with obesity. Additionally, mention the importance of screening for sleep disorders in patients with obesity and the potential benefits of addressing both sleep and weight issues concurrently.
The section comprehensively covers a range of potential strategies to improve sleep, addressing various lifestyle factors such as physical activity, diet, light exposure, caffeine intake, napping, alcohol consumption, and smoking.
The section appropriately connects the discussed strategies to their potential impact on metabolic health, aligning with the review's overall focus on the relationship between sleep and metabolic function.
This is a high-impact suggestion that would enhance the practical applicability and reader engagement of the section. While the section provides a good overview of potential strategies, it lacks specific, actionable recommendations for implementing these strategies. Providing more detailed guidance on how to incorporate these strategies into daily life would make the information more useful for readers seeking to improve their sleep and metabolic health. This enhanced practical guidance belongs in this section as it directly addresses the purpose of providing potential strategies for improving sleep. By offering concrete steps and examples, the review would empower readers to translate the scientific findings into real-world behavioral changes. This would strengthen the review's translational value and provide a more impactful resource for individuals seeking to improve their sleep and metabolic health. Ultimately, incorporating more specific, actionable recommendations would significantly enhance the practical utility of this section and increase its relevance for a broader audience.
Implementation: Provide more detailed and actionable recommendations for each strategy. For example, for physical activity, specify the recommended type, intensity, duration, and timing of exercise. For diet, provide examples of healthy eating patterns and specific foods to include or avoid. For light exposure, offer practical tips for increasing daytime light exposure and reducing evening blue light exposure. For example, 'Aim for at least 150 minutes of moderate-intensity aerobic exercise per week, spread throughout the week. Consume a balanced diet rich in fruits, vegetables, and whole grains, while limiting processed foods, sugary drinks, and saturated fats. Increase daytime light exposure by spending time outdoors, especially in the morning, and reduce evening blue light exposure by using blue light-blocking glasses or apps.'
This is a medium-impact suggestion that would improve the section's scientific rigor and provide a more nuanced understanding of the evidence base for the recommended strategies. While the section mentions the National Sleep Foundation as a source of further information, it would benefit from including specific citations for the studies supporting each strategy. This would allow readers to access the primary research and critically evaluate the evidence themselves. This enhanced referencing belongs in this section as it directly supports the scientific claims made about the effectiveness of each strategy. By providing specific citations, the review would increase the transparency and credibility of its recommendations. This would strengthen the review's scientific rigor and provide a more valuable resource for researchers and clinicians seeking evidence-based strategies for improving sleep. Ultimately, incorporating specific citations for each recommended strategy would significantly enhance the scientific quality of this section and increase its value for a scientific audience.
Implementation: Include specific citations for the studies supporting each strategy. Ensure that the cited studies directly address the specific recommendations made in the review. For example, when discussing the benefits of physical activity, cite studies that have specifically investigated the effects of exercise on sleep quality in the context of metabolic health.
The conclusion effectively synthesizes the key findings presented throughout the review, summarizing the impact of both insufficient sleep and circadian misalignment on metabolic health and obesity. It clearly reiterates the core message that both sleep quantity and timing are crucial for maintaining healthy metabolic function.
The conclusion appropriately highlights the significant increase in knowledge in the field over the past decade, emphasizing the growing recognition of sleep's importance in public health and clinical practice. This underscores the review's timeliness and relevance.
This is a high-impact suggestion that would strengthen the conclusion's contribution to the field by providing a more focused and actionable call to action. While the conclusion mentions the need for future studies and highlights key knowledge gaps, it would benefit from a more concise and specific list of research priorities. This would provide a clear roadmap for future research and facilitate progress in the field. This enhanced call to action belongs in the conclusion as it provides direction for future research based on the review's findings. By offering concrete research questions, the review would stimulate further investigation and accelerate progress in understanding the complex relationship between sleep, circadian rhythms, and metabolic health. Ultimately, incorporating a more specific and actionable call to action would significantly enhance the conclusion's impact and contribute to advancing the field.
Implementation: Replace the general reference to Box 3 with a concise and prioritized list of 3-5 key research priorities directly stemming from the review's findings. Focus on actionable research questions that can be addressed in future studies. For example, 'Future research should prioritize: 1) Investigating the long-term effects of chronic insufficient sleep and circadian misalignment on metabolic health using longitudinal study designs; 2) Examining the interplay between sleep, circadian rhythms, and the gut microbiome in the development of obesity; 3) Developing and testing targeted interventions to improve sleep and circadian health in populations at high risk for metabolic disorders.'
This is a medium-impact suggestion that would enhance the conclusion's broader impact and relevance. While the conclusion mentions the importance of sleep and circadian health, it would benefit from briefly discussing the potential societal and economic implications of poor sleep health. This would strengthen the argument for prioritizing sleep health as a public health issue. This discussion of societal impact belongs in the conclusion as it connects the scientific findings to real-world consequences. By highlighting the economic burden of poor sleep health, the review would underscore the importance of investing in research and interventions to improve sleep at a population level. Ultimately, including a brief discussion of societal and economic implications would broaden the conclusion's reach and strengthen the case for prioritizing sleep health as a public health concern.
Implementation: Add a brief paragraph discussing the potential societal and economic implications of poor sleep health. For example, 'The widespread prevalence of insufficient sleep and circadian misalignment poses a significant burden on society, contributing to reduced productivity, increased healthcare costs, and a higher risk of chronic diseases. Investing in public health initiatives to promote healthy sleep habits could yield substantial economic and societal benefits.'