The role of insufficient sleep and circadian misalignment in obesity

Table of Contents

Overall Summary

Overview

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%.

Key Points

Comprehensive Evidence Synthesis (written-content)
The review comprehensively synthesizes evidence from human studies, demonstrating the impact of insufficient sleep and circadian misalignment on energy expenditure, appetite hormones, and food choices.
Section: Introduction, Energy expenditure and appetite hormones, Impact of insufficient sleep, Impact of circadian misalignment, Combined effects
Clear Definitions (written-content)
The review clearly defines insufficient sleep and circadian misalignment, providing a framework for understanding their distinct and overlapping effects.
Section: Introduction, Impact of insufficient sleep, Impact of circadian misalignment
Integration of Concepts (written-content)
The review effectively connects the discussion of circadian misalignment to insufficient sleep, highlighting their combined impact on metabolic health.
Section: Impact of circadian misalignment, Combined effects
Critical Evaluation of Evidence (written-content)
The review acknowledges the limitations of cross-sectional studies and self-reported data, advocating for more longitudinal research.
Section: Circadian misalignment and obesity risk, Obesity and its effect on sleep
Effective Visualizations (graphical-figure)
Figures effectively communicate complex information, visually demonstrating the impact of sleep and circadian rhythms on energy expenditure and appetite hormones.
Section: Energy expenditure and appetite hormones, Impact of insufficient sleep, Circadian misalignment and obesity risk
Strengthen Historical Context (written-content)
While the review provides a comprehensive overview of sleep disruptors, it could strengthen the rationale by explicitly linking historical sleep patterns to the rise in obesity.
Section: Introduction
Expand Discussion of Gut Hormones (written-content)
While the review discusses GLP-1 and pancreatic polypeptide, expanding on their potential roles, even with limited data, would provide a more complete picture.
Section: Energy expenditure and appetite hormones, Impact of insufficient sleep
Explore Interactions (written-content)
While the review summarizes combined effects, exploring potential synergistic or antagonistic interactions between insufficient sleep and circadian misalignment would enhance mechanistic insights.
Section: Combined effects
Enhance Figure Detail (graphical-figure)
While figures are generally clear, adding more detail to Figure 3's brain representation and clarifying "baseline" conditions in Figure 2 would improve accuracy and interpretation.
Section: Energy expenditure and appetite hormones, Impact of insufficient sleep
Provide Actionable Strategies (written-content)
While the review covers potential sleep improvement strategies, providing more specific, actionable recommendations and citations would enhance practical applicability.
Section: Potential strategies to improve sleep

Conclusion

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.

Section Analysis

Abstract

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Strengths

Suggestions for Improvement

Introduction

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Energy expenditure and appetite hormones

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Non-Text Elements

Fig. 1. Energy expenditure in healthy adults is influenced by both sleep and...
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Fig. 1. Energy expenditure in healthy adults is influenced by both sleep and circadian processes.

First Reference in Text
Multiple components of energy metabolism are influenced by circadian and sleep-wakefulness processes, including energy expenditure75-77 and metabolic and appetite hormones78-83 (FIGS. 1,2 and 3).
Description
  • Overview of Figure Panels: Figure 1 shows how energy expenditure changes over a 24-hour period under different sleep and circadian conditions. Energy expenditure is the amount of energy the body uses, often measured in kilojoules (kJ). The x-axes typically represent time, either as hours from scheduled wake time, or as "relative clock hour" linked to the individual's melatonin onset. Melatonin is a hormone that regulates sleep, and its onset is used as a marker of the biological night. The y-axes represent energy expenditure, either in absolute units (kJ/min) or as a percentage change from a baseline. Panel (a) compares energy expenditure during a normal sleep schedule (16 hours awake, 8 hours of sleep) with a period of total sleep deprivation (24 hours awake). Panel (b) shows the inherent circadian rhythm of energy expenditure under constant conditions, meaning factors like light, food intake, and posture are carefully controlled to isolate the effect of the body's internal clock. Panel (c) shows energy expenditure during adequate and insufficient sleep, with or without controlling food intake. Panel (d) illustrates the impact of simulated night shift work (sleeping during the day) on energy expenditure.
  • Constant Routine Protocol: A constant routine protocol is a research method used in chronobiology to isolate the effects of the body's internal clock (the circadian rhythm) on physiological processes. Participants are kept in carefully controlled conditions, such as dim light, constant temperature, and regular small meals or continuous feeding, to minimize the influence of external factors. This method helps researchers identify the true circadian rhythm of a process, like energy expenditure, independent of other influences like sleep or food intake.
  • Thermic Effect of Food: The thermic effect of food, also known as diet-induced thermogenesis, refers to the increase in energy expenditure that occurs after eating a meal. It represents the energy the body uses to digest, absorb, and process the nutrients from the food.
  • Whole-Room Calorimeter: A whole-room calorimeter is a specialized chamber used to measure a person's energy expenditure. It precisely tracks oxygen consumption and carbon dioxide production, which are used to calculate energy expenditure. This method is highly accurate and sensitive compared to other methods like doubly labelled water.
  • Doubly Labelled Water: Doubly labelled water is another method used to estimate energy expenditure over longer periods, typically days or weeks. It involves giving a person water containing isotopes (slightly different forms) of hydrogen and oxygen. By measuring how these isotopes are eliminated from the body, researchers can estimate energy expenditure. This method is less precise than calorimetry but is more practical for free-living studies.
Scientific Validity
  • Methodological Rigor: The figure presents data from multiple published studies employing robust methodologies such as the constant routine protocol and whole-room calorimetry. This strengthens the scientific validity of the findings.
  • Experimental Design: The inclusion of both experimental and free-living data adds to the figure's comprehensiveness. Panel (c), in particular, highlights the importance of controlling for energy intake when assessing the impact of sleep on energy expenditure. However, the lack of a direct comparison between controlled and ad libitum feeding during circadian misalignment (panel d) limits the conclusions that can be drawn about the independent effects of circadian disruption.
  • Relevance to Paper's Argument: The figure effectively supports the paper's overall argument about the interplay between sleep, circadian rhythms, and energy metabolism. It visually demonstrates the distinct and combined effects of these factors on energy expenditure, providing compelling evidence for their importance in metabolic health.
Communication
  • Clarity of Take Away Message: The figure effectively communicates the main takeaway that energy expenditure is influenced by both sleep and circadian rhythms. The different panels showing different experimental conditions help to illustrate this point clearly. However, it would improve clarity to provide a brief explanation of what "relative clock hour" means within each panel, specifically referencing the relationship to melatonin onset.
  • Visual Presentation of Data: The visual presentation of the data is generally clear, using distinct lines and colors for different conditions. The inclusion of shaded areas to represent sleep periods is helpful. However, the b-spline smoothing in panels (b) and (d) might obscure some of the finer details of the data, particularly the raw fluctuations in energy expenditure. Showing the individual data points underneath the smoothed curves would allow for a more complete representation of the data.
  • Completeness of Caption: The figure caption provides a concise and accurate summary of the figure's content. However, it could be strengthened by explicitly mentioning the key finding that circadian rhythms in energy expenditure persist even under constant conditions, as shown in panel (b).
Fig. 2. The appetite-stimulating hormone ghrelin and the satiety hormones...
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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.

First Reference in Text
Multiple components of energy metabolism are influenced by circadian and sleep-wakefulness processes, including energy expenditure75-77 and metabolic and appetite hormones78-83 (FIGS. 1,2 and 3).
Description
  • Hormone Profiles and Conditions: This figure shows how the levels of different appetite-regulating hormones change throughout the day and night in healthy adults, and how these changes are affected by sleep and the body's internal clock. Ghrelin is a hormone that makes you feel hungry (appetite-stimulating), while leptin and PYY are hormones that make you feel full (satiety hormones). The figure displays 24-hour profiles of these hormones under two different conditions: normal daily routines and a "constant routine" protocol.
  • Habitual Condition Panels: Panels (a), (c), and (e) show the 24-hour patterns of ghrelin, leptin, and PYY, respectively, under normal living conditions, assuming adequate sleep and a balanced energy intake (referred to as "baseline" in the figure). The x-axis represents the time elapsed since waking up, and the y-axis represents the hormone concentration in the blood (pg/mL for ghrelin and PYY, ng/mL for leptin). The gray shaded areas represent the typical sleep period.
  • Constant Routine Panels: Panels (b), (d), and (f) show the circadian rhythms of these hormones under a "constant routine" protocol. This research method controls for external factors like light and meals to isolate the effect of the body's internal clock. Participants are kept in dim light, eat small, regularly timed snacks, and stay awake in a semi-recumbent position for at least 24 hours. The x-axis represents the circadian phase, with 0° corresponding to the onset of melatonin secretion (a marker of the biological night), and the y-axis represents the percent change in hormone levels from the average value. The gray shaded areas show the biological night based on the melatonin rhythm.
  • B-Spline: A b-spline is a mathematical function used to create smooth curves that fit to a set of data points. In this figure, b-splines are used to represent the average trends in hormone levels over time, smoothing out the short-term fluctuations.
  • Circadian Rhythm: Circadian rhythm is the body's natural, internal process that regulates the sleep-wake cycle and repeats roughly every 24 hours. It is driven by the body's internal "clock", which is influenced by external cues like light and dark.
Scientific Validity
  • Consistency with Literature and Methodology: The data presented are consistent with the established literature on the hormonal regulation of appetite and the influence of sleep and circadian rhythms. The use of the constant routine protocol is a scientifically sound method for isolating circadian effects, strengthening the validity of the circadian rhythm panels (b, d, f).
  • Generalizability: The figure relies on data from healthy adults, which limits the generalizability of the findings to other populations, such as individuals with obesity or sleep disorders. Future research should investigate how these hormone profiles might differ in these groups.
  • Feeding Paradigm in Constant Routine: The study from which the constant routine data are derived (Ref. 80) used hourly snacks to control energy intake. While this is a standard practice, it does not perfectly mimic the typical eating patterns of free-living individuals. More research using different feeding paradigms (e.g., larger, less frequent meals) would strengthen the conclusions about the independent effects of circadian rhythms on hormone secretion.
Communication
  • Overall Clarity: The figure successfully conveys the main point that appetite hormones are influenced by energy intake, sleep, and circadian rhythms. The separate panels illustrating habitual and constant routine conditions are helpful, and the consistent use of gray shading for the sleep/biological night period aids in visual comparison. However, the figure would benefit from a clearer explanation within the caption or figure itself about what constitutes "adequate sleep" and an "energy-balanced diet" in the habitual condition panels (a, c, e). Simply stating "baseline" is insufficient, as the reader needs to know the precise parameters of these baseline conditions for proper interpretation.
  • Data Presentation: The presentation of the data using smoothed curves (b-splines) is appropriate for showing overall trends. However, it also obscures the underlying variability in the data. Adding individual data points (perhaps with some transparency or jitter) underneath the smoothed curves would allow the reader to appreciate the extent of individual variation and the robustness of the average trends.
  • Synchronization with Meal Timing: While the labeling of meal times (B, L, D) in panels (a, c, e) provides some context, it would be helpful to include shaded regions or other visual cues to represent the timing and duration of meals in the constant routine panels (b, d, f) as well. This would facilitate direct comparison of the hormone profiles under different feeding conditions.
  • Caption Detail: The caption could be more explicit about the key takeaway messages of each panel. For example, stating that ghrelin peaks before meals and during early sleep, while leptin and PYY show opposite patterns. This would guide the reader towards the most important observations and reinforce the paper's main points.

Impact of insufficient sleep

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Fig. 3. Model of changes in appetite hormones, hunger and energy intake in...
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Fig. 3. Model of changes in appetite hormones, hunger and energy intake in response to insufficient sleep.

First Reference in Text
When energy intake is uncontrolled in lean adults during periods of insufficient sleep, an increase in energy intake occurs that is larger than the increase in energy expenditure, which results in a positive 24-h energy balance and weight gain76 (FIG. 4).
Description
  • Overview of Model: Figure 3 presents a simplified model explaining how insufficient sleep affects appetite hormones, hunger, and energy intake. The model shows interactions between the stomach, small intestine, adipose tissue (fat storage), the brain, and hunger levels. The model considers two scenarios: one where energy intake is controlled (to maintain energy balance as if the subject had gotten adequate sleep) and another where energy intake is freely chosen (ad libitum).
  • Controlled Energy Intake Scenario: The model illustrates that under insufficient sleep with controlled energy intake, ghrelin (a hormone that increases appetite) increases, while leptin (a hormone that decreases appetite) decreases. This hormonal shift leads to increased hunger. In this scenario, the energy intake is insufficient to compensate for the increased energy the body is expending due to being awake longer, resulting in a negative energy balance (more energy burned than consumed).
  • Ad Libitum Energy Intake Scenario: Conversely, when energy intake is ad libitum (unrestricted) during insufficient sleep, ghrelin decreases, and leptin and PYY (another appetite-suppressing hormone) increase. Despite this hormonal shift, which should reduce hunger, people tend to overeat. The increased food intake more than compensates for the extra energy expenditure caused by being awake longer, resulting in a positive energy balance and potential weight gain. The model suggests that factors beyond appetite hormones must be driving the increased energy intake in this situation.
  • Insufficient Sleep: Insufficient sleep refers to not getting enough sleep to support optimal physical and cognitive function. In this context, it's not necessarily about a specific number of hours, but rather about the quality and restorative nature of the sleep.
  • Ad Libitum: Ad libitum, in the context of dietary studies, means 'as desired' or 'freely chosen'. Participants are allowed to eat as much or as little as they want.
Scientific Validity
  • Hormonal and Behavioral Factors: The model is supported by experimental findings showing that sleep restriction alters levels of ghrelin, leptin, and PYY. However, the model simplifies the complex neuroendocrine control of appetite and does not fully account for all factors contributing to overeating during insufficient sleep. Other influences, such as changes in reward pathways, cognitive control, and emotional regulation, are likely also involved and could be incorporated into a more comprehensive model.
  • Hedonic Eating and Other Factors: The model accurately reflects the paradoxical finding that despite appetite-suppressing hormones increasing during insufficient sleep with ad libitum food access, energy intake still increases. This highlights the importance of factors beyond homeostatic appetite regulation, such as hedonic eating (eating for pleasure), in driving overconsumption. However, the model does not explicitly address these hedonic factors or their underlying mechanisms.
  • Neurobiological Mechanisms: The model lacks specific detail about the downstream effects of the hormonal changes depicted. For example, it does not explain how changes in ghrelin, leptin, and PYY specifically influence brain activity and subsequent feeding behavior. Adding more detail about the neurobiological pathways involved would strengthen the model's scientific rigor.
Communication
  • Clarity of Model: The figure clearly communicates the complex interplay between appetite hormones, hunger, and energy intake during insufficient sleep. The use of different panels to illustrate distinct dietary conditions (controlled vs. ad libitum) effectively highlights the paradoxical relationship between appetite hormones and actual energy intake when food is freely available. However, the model's representation of the brain could be enhanced by adding more detail or context. For example, including specific brain regions known to be involved in appetite regulation (e.g., hypothalamus, reward centers) would enhance the scientific accuracy and educational value of the figure.
  • Visual Appeal: The visual presentation of the model is simple and easy to understand, with clear icons and labels. The use of arrows effectively illustrates the directional relationships between different components of the model. However, the figure could benefit from a more visually engaging design. The current layout is somewhat basic and could be improved with more sophisticated graphics or a more dynamic representation of the interactions between hormones, brain, and behavior.
  • Caption Detail: The caption is concise and accurate, but could be more informative by explicitly mentioning the key takeaway message, which is that energy intake remains excessive during insufficient sleep even when appetite-reducing hormones increase, suggesting the involvement of other factors like reward pathways or cognitive control.
Fig. 4. Insufficient sleep affects energy intake and energy expenditure, which...
Full Caption

Fig. 4. Insufficient sleep affects energy intake and energy expenditure, which leads to a positive energy balance and the risk of weight gain.

First Reference in Text
When energy intake is uncontrolled in lean adults during periods of insufficient sleep, an increase in energy intake occurs that is larger than the increase in energy expenditure, which results in a positive 24-h energy balance and weight gain76 (FIG. 4).
Description
  • Overview of Flowchart: This figure is a flowchart illustrating how insufficient sleep can lead to weight gain. It presents a chain of events, starting with insufficient sleep and ending with a positive energy balance and increased risk of weight gain. The figure differentiates between two scenarios based on energy intake: one where energy intake is controlled, and the other where intake is ad libitum (freely chosen).
  • Effects of Insufficient Sleep: Insufficient sleep increases 24-hour energy expenditure (the total amount of energy the body burns in a day). However, it also affects appetite hormones (chemical messengers that regulate hunger and fullness).
  • Controlled Energy Intake: When energy intake is controlled to maintain energy balance at the level needed for a typical day with adequate sleep, the increased energy expenditure combined with unchanged or insufficient energy intake leads to a *negative* energy balance (more energy burned than consumed). In this scenario, ghrelin (an appetite-stimulating hormone) increases, while leptin (an appetite-suppressing hormone) decreases, leading to increased appetite. This makes intuitive sense: the body is trying to compensate for the energy deficit.
  • Ad Libitum Energy Intake: When energy intake is ad libitum (unrestricted), individuals tend to overeat during insufficient sleep. The increased food intake more than compensates for the increased energy expenditure, resulting in a *positive* energy balance (more energy consumed than burned). This positive energy balance, if sustained, leads to weight gain. Paradoxically, under these conditions, ghrelin decreases, and leptin increases, suggesting a hormonal drive to *reduce* appetite. This indicates that factors beyond appetite hormones are driving the overeating, potentially related to changes in reward pathways or cognitive control in the brain.
  • Energy Balance and Weight Gain: A positive energy balance means that you consume more calories than your body burns. A negative energy balance means you burn more calories than you consume. Weight gain occurs when there's a sustained positive energy balance.
  • Appetite Hormones: Appetite hormones are hormones that regulate hunger and fullness. Ghrelin increases appetite, while leptin and PYY decrease appetite.
Scientific Validity
  • Accuracy of Representation: The figure accurately represents the key findings of experimental studies on sleep restriction and energy balance. The distinction between controlled and ad libitum energy intake is crucial, as it highlights the complex and sometimes counterintuitive effects of sleep on appetite hormones and eating behavior.
  • Experimental vs. Real-World Settings: The figure relies on experimental evidence from controlled laboratory studies, which enhances its scientific validity. However, it's important to note that these findings may not fully translate to real-world settings where other factors, such as stress, social influences, and food availability, also play a role in energy balance. More research is needed to investigate the long-term effects of insufficient sleep on weight gain in free-living individuals.
  • Scope of Figure: The figure appropriately focuses on the impact of insufficient sleep on energy balance, which is a key factor in weight regulation. However, it doesn't address other potential health consequences of insufficient sleep, such as increased risk of metabolic disorders like type 2 diabetes. A more comprehensive figure could incorporate these broader health implications.
Communication
  • Clarity and Simplicity: The flowchart style effectively visualizes the cause-and-effect relationship between insufficient sleep and weight gain, making the complex interplay of factors easy to grasp. The use of plus and minus symbols to represent positive and negative energy balance is intuitive and reinforces the key message. However, the figure's simplicity could also be considered a limitation, as it doesn't fully capture the nuances of the interactions involved. For instance, the figure could be enhanced by visually separating the two scenarios described in the text: one with controlled energy intake and one with ad libitum intake. This would clarify the paradoxical effects of insufficient sleep on appetite hormones and energy balance.
  • Placement of Asterisk: The placement of the asterisk and the corresponding note about opposite effects under ad libitum conditions is somewhat unclear. It would improve readability to incorporate this information directly into the flow of the diagram. For instance, the "Appetite Hormones" box could be split into two branches, one for controlled intake and one for ad libitum intake, each showing the corresponding hormonal changes.
  • Lack of Mechanistic Detail: While the figure effectively conveys the overall message, it lacks specific details about the mechanisms involved. For example, it doesn't explain *how* insufficient sleep leads to increased energy expenditure or increased energy intake. Adding brief annotations or linking this figure to other figures illustrating these mechanisms would enhance its scientific value.

Impact of circadian misalignment

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Combined effects

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Circadian misalignment and obesity risk

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Non-Text Elements

Fig. 5. Circadian misalignment affects energy intake and appetite hormones,...
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Fig. 5. Circadian misalignment affects energy intake and appetite hormones, which potentially leads to a positive energy balance and the risk of weight gain.

First Reference in Text
Findings from rodent models indicate that the consumption of calories during the circadian time typically reserved for sleep leads to more weight gain than consumption of the same number of calories during the circadian time typically reserved for wakefulness134,153 These findings highlight that, even without changes in energy intake, weight gain could ensue when energy is consumed at inappropriate circadian times (FIG. 5).
Description
  • Overview of flowchart: Figure 5 presents a flowchart illustrating how circadian misalignment can potentially lead to weight gain. Circadian misalignment refers to a mismatch between the body's internal clock and the external environment, often caused by factors like shift work, jet lag, or irregular sleep schedules. The figure highlights the effects of this misalignment on energy expenditure, appetite hormones, food choices, and ultimately, energy balance.
  • Reduced energy expenditure: Circadian misalignment is shown to decrease 24-hour energy expenditure (the total amount of energy the body burns in a day). This is primarily due to reduced energy expenditure during sleep when sleep occurs during the biological daytime.
  • Mixed findings on energy intake: The figure acknowledges that the effects of circadian misalignment on energy *intake* are less clear. While some studies suggest that misalignment leads to poorer food choices and/or eating at inappropriate circadian times, the overall effect on total energy intake is uncertain, hence the question mark in the figure. The figure also notes that some evidence suggests that circadian misalignment leads to poor food choices or food quality which, over time, might contribute to a positive energy balance. For example, increased consumption of highly processed or sugary foods.
  • Appetite hormones and energy balance: Circadian misalignment is shown to alter appetite hormones (chemical messengers that regulate hunger and fullness). Specifically, it decreases PYY and leptin (hormones that promote satiety or feelings of fullness) and may increase ghrelin (a hormone that stimulates appetite). These hormonal changes, in combination with the reduced energy expenditure and potentially unhealthy food choices, can create a state of positive energy balance, meaning that more calories are consumed than burned.
  • Positive energy balance and obesity risk: A positive energy balance, if sustained over time, leads to weight gain and increases the risk of obesity.
  • Hormonal changes under controlled energy intake: The figure also includes a note at the bottom stating that when energy intake is controlled (meaning it is fixed to match the needs for energy balance with adequate night-time sleep at baseline), circadian misalignment leads to decreases in leptin and PYY and potentially increases ghrelin. This suggests that the hormonal changes associated with circadian misalignment occur independently of changes in how much a person eats.
Scientific Validity
  • Scientific basis: The figure is grounded in established scientific findings on the effects of circadian misalignment on energy expenditure and appetite hormones. The citations provided support the claim that mistimed eating can lead to weight gain, even without changes in total caloric intake. This highlights the importance of considering not only *how much* we eat but also *when* we eat.
  • Acknowledgement of uncertainty: The figure acknowledges the uncertainty surrounding the effects of circadian misalignment on total energy intake in humans. This is an important point, as the evidence in this area is indeed mixed. The use of a question mark to represent this uncertainty is appropriate and encourages further research to clarify this relationship.
  • Generalizability from rodent models: While the figure cites evidence from rodent models regarding the impact of mistimed eating on weight gain, it's important to note that these findings may not fully translate to humans. Human eating patterns and metabolic responses are more complex and can be influenced by a wider range of factors. More research is needed to directly investigate the long-term effects of circadian misalignment on energy intake and weight gain in human populations.
Communication
  • Overall clarity and simplicity: The figure effectively communicates the potential link between circadian misalignment, altered energy metabolism, and weight gain. The flowchart format clearly presents the sequence of events, starting with circadian misalignment and ending with potential obesity risk. The use of a question mark to acknowledge the uncertainty surrounding changes in energy intake is appropriate, reflecting the current state of the research. However, the figure's visual simplicity could also be a limitation. Adding more visual detail about the types of metabolic changes or unhealthy food choices associated with circadian misalignment would enhance its communicative power and provide a more complete picture of the phenomenon.
  • Caption detail: The figure's caption clearly summarizes the main message. However, it would benefit from a more explicit statement about the mixed findings regarding energy intake during circadian misalignment. This would reinforce the uncertainty represented by the question mark in the diagram and encourage further research in this area.
  • Detail of hormonal changes: The figure could benefit from a more detailed representation of the "Appetite Hormones" box. Breaking it down to show the specific changes in individual hormones (e.g., decreased leptin, PYY; increased ghrelin) would strengthen the link between circadian misalignment and appetite regulation.
  • Inclusion of broader metabolic consequences: While the figure focuses on the potential for weight gain, it would be beneficial to include other adverse metabolic consequences of circadian misalignment, such as increased risk of insulin resistance, type 2 diabetes, and cardiovascular disease. This would broaden the scope of the figure and emphasize the wider health implications of circadian disruption.

Obesity and its effect on sleep

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Potential strategies to improve sleep

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Conclusions

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