Does Sleep Curtailment Stimulate Appetite, Motivation to Eat and Dietary Intake in Humans? A Narrative Synthesis of Evidence and Considerations for Future Studies

ABSTRACT

Insufficient sleep has been increasingly recognised as a risk factor for obesity, yet the underlying mechanisms remain incompletely understood. Research suggests that sleep restriction promotes excessive dietary intake, and it is commonly assumed that this relationship can be explained by appetite dysregulation. Human appetite is multifaceted and includes homeostatic appetite regulation (governed by energy balance), hedonic responses to food and motivation to eat. However, these appetitive dimensions have rarely been considered together when understanding the links between sleep restriction and excessive dietary intake. Having employed a systematic literature search, this review synthesises evidence from human randomised, controlled trials within a comprehensive conceptual framework to critically examine the veracity of assumptions on whether sleep restriction heightens appetite sensations and, subsequently, increases dietary intake. This review demonstrates that the effects of sleep restriction on appetite and motivation to eat were inconsistent and often incongruent with observed changes in dietary intake. In many cases, higher energy intake following sleep restriction was not explained by corresponding changes in appetite or motivation to eat, challenging prevailing assumptions about causal pathways. We propose that these inconsistencies are likely driven, at least in part, by methodological limitations and the lack of an integrative framework that guides study design and interpretation. This review highlights that a structured framework that explicitly links sleep, appetite and dietary intake is imperative and should be used to identify key gaps and sources of discordance in the literature. We conclude by outlining recommendations to advance research in this area in the future.

1. Sleep, Appetite and Dietary Intake: A Conceptual Framework

Obesity is a complex and persistent public health challenge, driven by a combination of biological, behavioural and socioeconomic factors, including diet, genetics, stress and social environment (Masood and Moorthy 2023). Insufficient sleep has emerged as an important, yet often underappreciated, contributor to weight gain. Observational evidence consistently demonstrates associations between short sleep duration and higher BMI (Bacaro et al. 2020) in both children (Deng et al. 2021) and adults (Jiang et al. 2024). These relationships appear to be driven by behavioural mechanisms, with experimental studies indicating that sleep restriction increases energy intake (Jiang et al. 2024) and reduces physical activity (Schmid et al. 2009). Collectively, these findings suggest that inadequate sleep may influence both sides of the energy balance equation.

Since human energy intake is governed by appetite (defined as the absence of hunger and the anticipation of food reward (Rogers and Brunstrom 2016)), it is hypothesised that the effects of short sleep on higher energy intake are mediated through a variety of appetitive mechanisms such as heightened hunger and blunted fullness sensations. In addition, several studies have also reported that insufficient sleep contributed to increased food cravings (Yang et al. 2019), preference for sweeter foods and beverages (Szczygiel et al. 2019a, 2019b) and higher desire for energy‐dense foods (Greer et al. 2013). These appetitive changes were assumed to increase subsequent energy intake.

Insufficient sleep has been associated with several neurobiological changes that may plausibly influence appetite and energy intake. These alterations can be broadly described as follows: (i) heightened sensitivity of the brain to food reward stimuli (Benedict et al. 2012; Demos et al. 2017; Hanlon et al. 2005; Horne 2015) and (ii) higher ghrelin (Greer et al. 2013; Taheri et al. 2004) and neuropeptide orexin hormone levels, where both of these are orexigenic hormones shown to stimulate appetite and the intake of palatable foods in animals (Muthmainah et al. 2021). Collectively, these responses should then translate into stronger appetite sensations that increase food intake.

To our knowledge, only one systematic review of clinical trials that examined the effects of sleep alterations on subjective appetite ratings in humans has been published (Soltanieh et al. 2021). In this review, the authors concluded that sleep restriction significantly increased hunger sensation, but this was the only appetite sensation considered. Since subjective appetite sensations in humans are multifaceted and include fullness and desire to eat, the consideration of hunger sensation alone prevents a holistic understanding of the effects of insufficient sleep on appetite and intake.

Drawing on existing literature (Blundell et al. 2010; Rogers and Hardman 2015), we developed a comprehensive conceptual framework to address the limited integration of subjective appetite sensations within existing models of sleep and energy intake (Figure 1). In this framework, we propose that dietary intake, the outcome, is influenced by humans' ‘motivation to eat’, which encompasses measurements such as desire to eat, food reward, wanting and food craving. Motivation to eat, in turn, is influenced by appetite sensations that are regulated via homeostatic and hedonic processes. ‘Homeostatic’ appetite sensations are decided by energy balance or needs and encompass satiation sensations (e.g., hunger, fullness, prospective eating) that govern the initiation and cessation of intake at an eating occasion, as well as satiety sensations that determine the length of time before the initiation of the next meal. In contrast, hedonic appetite sensations are not determined by energy needs but are instead based on one's liking and/or preference for a particular food.

FIGURE 1.

A conceptual framework relating sleep to homeostatic and non‐homeostatic appetitive sensations, which influence motivation to eat and subsequent dietary intake.

To our knowledge, there is no review that has examined the effects of sleep restriction on dietary intake via a comprehensive appetite framework concurrently, which forms the aim of this review. To achieve this aim and to ensure that all relevant publications are captured, we conducted a systematic search using the PRISMA 2025 guidelines of randomised controlled trials that manipulated sleep durations and measured subjective appetite and dietary intake within the same study (please refer to Table S1 for methods).

In total, 11 publications from 10 clinical trials were identified and analysed in this section. The details of these studies are summarised in Table S2. Overall, the design of these studies differed in the following major aspects: (i) length of sleep manipulation, with 9/11 studies restricting sleep to between 4 and 5 h per night and 6/11 studies restricting for two nights or fewer, (ii) type and timing of subjective appetite measurements taken (fasted or after meal challenge) (see Table S2), (iii) dietary intake assessment methods (ranging from single meal to 24‐h and intake at breakfast, lunch and/or as snacks). For the purpose of this review, an overview of the findings is provided in Table 1 based on the framework in Figure 1, while details of individual studies such as participant demographics and sleep interventions can be found in Table S2.

TABLE 1.

An overview of findings from 11 studies that examined the effects of sleep restriction on appetite, motivation to eat and dietary intake.

Study	Sleep restriction	Appetite			Motivation to eat	Dietary intake
		Satiation	Satiety	Hedonics
Brondel 2010	1 night	↑ Hunger	—	↔ Pleasantness of foods	↔ Desire to eat	↑ Energy, fat intake
Chamorro 2023	1 night	↑ Hunger	↔ Satiety	—	↔ Desire to eat	↑ Energy, protein, fat intake
						↔ CHO intake
McNeil 2017	1 night	↑ Hunger, prospective eating ↓ Fullness (all in advanced wake time group only)	—	↑ Liking of high fat foods (in advanced wake time group only)	↑ Desire to eat, desire for fatty foods (in advanced wake time group only)	↔ Energy, CHO, protein, fat intake
Yang 2021	1 night	↑ Hunger ↓ Fullness	—	—	↑ Desire to eat	↔ Energy, CHO, protein, fat intake
Hart 2015	2 nights	↔ Hunger	—	—	—	↓ Protein intake
						↔ Energy, CHO, fat intake
Schmid 2009	2 nights	↔ Hunger	↔ Satiety	—	—	↔ Energy, CHO, protein, fat intake
Radcliffe 2021	3 nights	Fasted: ↓ Prospective eating ↔ Hunger, fullness After test meal: ↓ Hunger, prospective eating ↑ Fullness			↓ Desire to eat (fasted & post‐test meal)	↑ Energy, CHO intake (Day 1–3)
			—	—		↓ Energy intake (in meal challenge) ↔ Protein, fat intake (in meal challenge)
Tajiri 2020	3 nights	↔ Hunger			↔ Desire for sweet & fatty foods	↑ Energy & CHO (g) intake (Day 1 & 3 only)
			—	—		↔ Protein & fat intake (Day 1 & 3 only)
Tajiri 2023	3 nights	↑ Hunger	—	—	↑ Desire for fatty foods	↑ Energy & CHO (g) intake at BF
						↔ Protein & fat intake
Hanlon 2016	4 nights	↑ Hunger, prospective eating	—		↑ Desire to eat
		↔ Fullness		↓ Liking of palatable foods		↔ Energy, CHO, protein, fat intake
St‐Onge 2011	5 nights	↓ Fullness (in men only)	↔ Satiety	—	↔ Desire to eat fruit, vegetables, sweet, savoury, salty foods	↑ Energy, fat, saturated fat intake
		↔ Hunger, prospective eating				↔ CHO, protein intake

Note: Shaded boxes represent results that aligned with the hypotheses that short sleep led to heightened appetite and dietary intake.

Abbreviations: ↑, significantly higher after sleep curtailment; ↓, significantly lower after sleep curtailment; ↔, not significantly different between usual and sleep curtailment; BF, breakfast; CHO, carbohydrate; VAS, visual analog scales.

2. What Are the Effects of Sleep Restriction on Appetite and Dietary Intake?

2.1. Effects of Sleep on Within‐Meal Satiation (Homeostatic)

In terms of homeostatic appetite regulation (e.g., hunger, fullness and prospective eating), all studies reported on hunger sensations. Seven studies reported significantly higher hunger levels after sleep restriction for one, three or four nights (Brondel et al. 2010; Chamorro et al. 2023; Hanlon et al. 2016; McNeil et al. 2017; Tajiri et al. 2020, 2023; Yang and Tucker 2021). Of these studies, one examined the effects of the timing of the restriction on appetite outcomes and noted that the hunger‐stimulating effects of sleep restriction were seen only when restriction derived from advanced wake time compared to a delayed bedtime (McNeil et al. 2017). The remaining four studies did not observe significant differences in hunger levels over two to five nights of restriction (Hart et al. 2015; Radcliffe et al. 2021; Schmid et al. 2009; St‐Onge et al. 2011).

Fullness was measured in five studies (Hanlon et al. 2016; McNeil et al. 2017; Radcliffe et al. 2021; St‐Onge et al. 2011; Yang and Tucker 2021). Three of these studies observed significantly lower fullness levels after sleep curtailment over one to five nights; one noted reduced fullness under fasting conditions (Yang and Tucker 2021), another observed reduced fullness only in the advanced wake time condition (McNeil et al. 2017) and the third reported reduced fullness in males only (St‐Onge et al. 2011). Contrary to the hypothesis that sleep restriction reduces sensations of fullness, one study (Radcliffe et al. 2021) documented higher fullness levels after a test meal in the curtailment condition. The remaining study (Hanlon et al. 2005) did not observe any difference in fullness sensation between sleep conditions.

Finally, prospective eating was assessed in four studies (Hanlon et al. 2016; McNeil et al. 2017; Radcliffe et al. 2021; St‐Onge et al. 2011). Two studies reported higher prospective eating ratings after three to four nights of sleep restriction (Hanlon et al. 2016; McNeil et al. 2017). Notably, this effect was observed only under an advanced wake‐time condition compared with usual sleep (McNeil et al. 2017). One study reported no difference in prospective eating ratings after five nights of curtailment (St‐Onge et al. 2011); whereas, another observed lower prospective eating scores (contrary to hypothesis) in both the fasted and fed states following three nights of two‐hour sleep opportunity (Radcliffe et al. 2021).

Overall, the effects of sleep restriction on all homeostatic satiation measurements such as hunger, fullness and prospective eating were mixed and inconclusive. Possible explanations for these discrepancies are discussed below (Section 4).

2.2. Effects of Sleep on Between‐Meal Satiety (Homeostatic)

Only three studies measured satiety (Chamorro et al. 2023; Schmid et al. 2009; St‐Onge et al. 2011). The studies ranged in duration from one to five nights. None of the studies reported an effect of sleep manipulation on satiety. Based on the limited available data, satiety does not seem to be affected by sleep curtailment.

2.3. Effects of Sleep on Food Hedonics

Three studies assessed hedonic perceptions, that is, liking and perceived pleasantness of foods (Brondel et al. 2010; Hanlon et al. 2016; McNeil et al. 2017) and reported mixed results. In one study, an advanced wake time after one night resulted in higher liking ratings of high fat foods but only when compared to the control group and not the delayed wake time group (McNeil et al. 2017). One study that utilised a one‐night restriction did not find any differences in the ratings of the pleasantness of foods (Brondel et al. 2010); while the remaining study used a four‐night restriction protocol and documented lower liking for palatable foods (Hanlon et al. 2016), which was contrary to the hypothesis that sleep curtailment would increase participants' liking of foods. Based on the limited available evidence, hedonic liking of foods does not appear to be consistently affected by sleep.

2.4. Effects of Sleep on Motivation to Eat

Across nine studies assessing motivation to eat, findings were also variable (Brondel et al. 2010; Chamorro et al. 2023; Hanlon et al. 2016; McNeil et al. 2017; Radcliffe et al. 2021; St‐Onge et al. 2011; Tajiri et al. 2020, 2023; Yang and Tucker 2021). Four studies reported increases in general desire to eat with restrictions of one to four nights (Hanlon et al. 2016; McNeil et al. 2017; Tajiri et al. 2023; Yang and Tucker 2021), with one of these studies observing higher desire to eat only in the advanced wake time sleep restriction condition (McNeil et al. 2017). Other studies noted increased desire to eat fatty (but not sweet) foods over 16 h (Tajiri et al. 2023), but not at breakfast (Tajiri et al. 2020). Of the remaining four studies that utilised sleep restriction protocols between one and five nights, three studies reported no difference in general desire to eat (Brondel et al. 2010; Chamorro et al. 2023) or desire to eat fruit, vegetables or something sweet, savoury or salty (St‐Onge et al. 2011). Consistent with findings for other appetitive outcomes, the study employing the most extreme sleep curtailment protocol (two‐hour sleep for three nights) reported effects contrary to the hypothesised direction, that is, significantly lower desire to eat in both the fasted and fed states was observed following sleep curtailment (Radcliffe et al. 2021). Overall, sleep curtailment may be more likely to increase motivation to eat than decrease it; although, the prevalence of null findings impedes firm conclusions.

2.5. Effects of Sleep on Dietary Intake

Five studies investigated the effects of sleep restriction on single‐meal intake (Hart et al. 2015; McNeil et al. 2017; Radcliffe et al. 2021; Tajiri et al. 2020; Yang and Tucker 2021). Two studies that applied sleep restriction for one night did not find differences in dietary intake (McNeil et al. 2017; Yang and Tucker 2021). A study that applied two nights of sleep restriction found a higher percentage of energy derived from protein, despite no significant differences in total energy intake (Hart et al. 2015). Two studies examining three nights of sleep restriction reported significant effects on dietary intake, although in opposing directions. One study observed higher energy and carbohydrate intake at breakfast (Tajiri et al. 2020), whereas another reported lower energy intake following three nights of a two‐hour sleep opportunity per night (Radcliffe et al. 2021).

Seven studies also reported dietary intake beyond one meal (Brondel et al. 2010; Chamorro et al. 2023; Hanlon et al. 2016; Schmid et al. 2009; St‐Onge et al. 2011; Tajiri et al. 2023; Yang and Tucker 2021). After one‐night curtailment, two out of three studies reported higher energy intake (Brondel et al. 2010; Chamorro et al. 2023) while another study found no effect (Yang and Tucker 2021). All three studies did not find differences in carbohydrate intake, while protein and fat intake was found to be higher in one (Chamorro et al. 2023) and two (Brondel et al. 2010; Chamorro et al. 2023) studies respectively. The remaining four studies restricted sleep for more than one night (Hanlon et al. 2016; Schmid et al. 2009; St‐Onge et al. 2011; Tajiri et al. 2023): Two studies did not observe a difference in dietary intake (Hanlon et al. 2016; Schmid et al. 2009); one study found higher intake of snacks on Day 3 of the experiment but this did not alter total daily energy intake (Tajiri et al. 2023); and the fourth study documented higher energy, fat and saturated fat intake, but not protein and carbohydrate, after sleep curtailment (St‐Onge et al. 2011).

3. Is There Congruency Between Sleep, Appetite and Intake Measurements?

To determine congruency, that is, whether changes in appetite consistently influence motivation to eat and subsequently dietary intake in the expected direction during sleep restriction, the complex inter‐relationships between sleep, appetite and dietary intake from the 11 studies are synthesised and presented in Figure 2. In this figure, studies are grouped under the three aspects illustrated in the conceptual framework (Figure 1): (i) ‘appetite’ that influences (ii) ‘motivation to eat’, and, in turn, (iii) ‘dietary intake’. In Figure 2, studies in white boxes are those consistent with the hypothesis that sleep restriction promotes at least one measurement of appetite (as higher hunger and prospective eating or lower fullness), stimulates motivation to eat and results in higher dietary intake. Black boxes represent studies that contradicted the hypothesis, while grey boxes are studies that did not observe significant differences between usual and short sleep conditions. If the evidence is congruent, the findings would appear as white boxes consistently across appetite, motivation to eat and dietary intake to support the hypothesis that sleep restriction stimulates appetite and food intake.

FIGURE 2.

The lack of congruency of evidence supporting the hypothesis that sleep curtailment increases dietary intake via stimulation of appetite and motivation to eat. Appetite includes satiation, satiety and food hedonics. White boxes—Significantly higher in at least one appetite, motivation to eat and dietary intake measurements after sleep restriction (hypothesised effects). Black boxes—Significantly lower only in at least one satiation/satiety/food hedonic measurements and motivation to eat after sleep restrictions (contradicting effects). Grey boxes—No significant differences between sleep conditions in all appetite and dietary measures (no effect).

Three key observations arise from this figure. First, the effects of sleep on appetite and motivation to eat varied and were inconsistent between studies. Second, only four studies showed that sleep curtailment significantly increased appetite and food intake (Brondel et al. 2010; Chamorro et al. 2023; St‐Onge et al. 2011; Tajiri et al. 2023); however, three of these studies found no significant differences in participants' motivation to eat (Brondel et al. 2010; Chamorro et al. 2023; St‐Onge et al. 2011). Third, incongruency was observed where significantly higher intake was not explained by appetite and motivation to eat (Radcliffe et al. 2021; Tajiri et al. 2020) or where higher appetite and motivation to eat did not result in higher intake (Hanlon et al. 2016; McNeil et al. 2017; Yang and Tucker 2021). Among all available studies, only one study consistently showed that sleep restriction increased appetite and motivation to eat and subsequently dietary intake (Tajiri et al. 2023).

4. Plausible Explanations and Considerations for Incongruency of the Evidence

The lack of congruency between sleep, appetite, motivation to eat and dietary intake from available evidence suggests two possibilities: (1) that sleep restriction had no true effect on appetite, motivation to eat and dietary intake or (2) that methodological issues may have influenced the findings from these studies. While the former possibility is plausible, we argue that the latter may be more likely. In this section, we offer some plausible explanations and considerations for future studies in this field.

4.1. Consideration 1: Type, Severity and Duration of Sleep Deprivation

This review reveals a number of issues in sleep and appetite research. The variability in sleep restriction protocols—in terms of duration (number of nights the protocol was implemented) and severity (number of hours of sleep allowed per night)—likely contributes to uncertainty and lack of congruence in the findings. Reports on the effects of sleep quality are notably absent. Each of these is discussed below.

Regarding the duration of curtailment, four of the studies included in this review applied sleep curtailment only over one night (Brondel et al. 2010; Chamorro et al. 2023; McNeil et al. 2017; Yang and Tucker 2021), while the rest restricted sleep over two‐ (Hart et al. 2015; Schmid et al. 2009), three‐ (Radcliffe et al. 2021; Tajiri et al. 2020, 2023), four‐ (Hanlon et al. 2016) or five‐nights (St‐Onge et al. 2011). Although there was no clear pattern of influence on results, it is important to point out that all studies reporting no effects of sleep curtailment on hunger (Hart et al. 2015; Radcliffe et al. 2021; Schmid et al. 2009; St‐Onge et al. 2011) applied sleep restriction for more than one night. This suggests that the effect of sleep on hunger was either acute or that adaptation to higher hunger occurred after multiple days of sleep restriction. Future research is needed to distinguish between these possibilities.

In terms of the severity of sleep curtailment, protocols ranged from 2 h of sleep per night up to 6 h per night. While it is logical to assume that more severe sleep curtailment leads to increased appetite and dietary intake dysregulation, this was not the case and there was no clear trend from the studies included in this review. In fact, the study that applied the most severe sleep curtailment reported findings that were contrary to the hypothesised effects, that is, sleep curtailment led to lower appetite and motivation to eat, although dietary intake was found to be significantly higher (Radcliffe et al. 2021). In contrast, another study not included in this review due to the lack of dietary intake data reported total sleep deprivation had no significant effect on hunger (Chan 2024). It is not immediately clear how these differences can be reconciled. In summary, the available data fail to suggest a ‘break point’ at which changes in appetite and intake are reliable and congruent.

The studies in this review focused on sleep duration interventions but did not examine the effects of changes of sleep quality on appetite and intake. Together, sleep quantity and quality provide a holistic view of sleep health. Both are independent risk factors for chronic disease risk (Anothaisintawee et al. 2016; Lao et al. 2018) and while sleep duration is the focus of public health messaging, poor sleep quality may have greater adverse effects on health than duration (Andreasson et al. 2021). Measurements of sleep quality may provide additional insight into how sleep affects appetite and intake.

4.2. Consideration 2: Appetite Assessment Methods

In terms of appetite, all studies assessed the combination of satiation (predominantly as hunger sensations) and satiety sensations, while only 3 studies measured hedonic perception of foods after sleep manipulation. Since satiation and satiety are governed by energy homeostasis, this implies that previous sleep curtailment studies had hypothesised an effect of sleep on energy balance. From a mechanistic perspective, there is some evidence that sleep restriction increases energy expenditure (Jung et al. 2011), which theoretically can induce negative energy balance and stimulate homeostatic hunger as a consequence. However, several studies have also reported that sleep curtailment did not alter energy expenditure (Calvin et al. 2013; Covassin et al. 2022) or even reduced it (Benedict et al. 2011). Therefore, there is currently no strong scientific evidence to believe that homeostatic appetite ratings can be influenced by sleep curtailment, regardless of how logical this might seem. The implication is that measuring post‐sleep‐curtailment appetite ratings that are dictated by homeostatic energy balance alone may not be adequate to understand how sleep restriction may have an impact on motivation to eat and dietary intake.

On the other hand, non‐homeostatic appetite regulation, that is, hedonic liking towards foods, in response to sleep curtailment was not well‐investigated. Hedonic appetite ratings are highly relevant in sleep research as our previous systematic review demonstrated that preference for sweet taste was heightened by sleep restriction (Tucker et al. 2025), which has the potential to drive food intake and lead to obesity in the long‐term (Finlayson and Dalton 2012). In another study, it was also observed that sleep restriction led to significantly higher craving for chocolate, higher energy intake at breakfast and the selection of bigger portion sizes for carbohydrate‐rich foods such as rice and potato (Yang et al. 2019). However, the evidence of the effects of sleep curtailment on hedonic appetite measures is not consistent across the studies included in this paper. Regardless, it is important for future sleep research to consider both homeostatic and hedonic (non‐homeostatic) appetite measurements in order to gain a more complete and sophisticated understanding of the dynamic interactions between homeostatic and hedonic appetite sensations following sleep curtailment. This, in turn, will improve our understanding of how sleep impacts motivation to eat, especially on food reward, wanting, craving and the subsequent intake of palatable foods, which have been implicated in obesity (Berthoud 2012; Hall et al. 2014). Work exploring whether sleep restriction differentially affects individuals with characteristics like high dietary restraint or increased engagement in emotional eating may also help to improve congruency of outcomes. This supposition stems from a recent review that concluded emotional eating and dietary disinhibition mediate the relationship between insufficient sleep and obesity, particularly in women (Zerón‐Rugerio et al. 2023).

Next, the timing of appetite measurements should be carefully considered, as well. It is logical to assess appetite and motivation to eat immediately upon waking (in a fasted state), as the effects of sleep curtailment on appetite are expected to be strongest at this time. Studies included in this review also investigated the impact of sleep curtailment on appetite periodically (e.g., every 30 min or 2 h) over a period of time ranging from 3 (McNeil et al. 2017) to 19 h (Tajiri et al. 2020, 2023). The variation in the appetite scales and timing of appetite assessment, when combined with variations in which aspects of appetite were measured (e.g., hunger, fullness etc.) and how results are presented (as absolute values vs. area under the curves (Tajiri et al. 2023; Yang and Tucker 2021)), has no doubt contributed to the inconsistent findings and added complexity to the comparison of outcomes from different studies.

Finally, subjective appetite measurements using tools such as visual analogue scales are susceptible to low sensitivity and high variability due to several factors including differences in how individuals use the scales and the environment where experiments are conducted (Flint et al. 2000; Stubbs et al. 2000). Due to high variations, bigger samples sizes are likely needed to achieve statistical significance, which may not always be feasible. All studies in this review used a crossover study design where measurements were repeated in the same participants under standardised conditions and participants served as their own control. This study design can reduce variability generated by the use of VAS (Flint et al. 2000).

4.3. Consideration 3: Dietary Intake Assessment and Length of Effects

Another important observation that arises from this review is that dietary intake assessment differed among these studies in a number of aspects. For example, dietary intake was assessed at one meal in some studies or multiple meals throughout a day in others. The decision to assess dietary intake at a meal vs. all day should be guided by the aims and hypotheses of the studies. Assessing intake at the first meal after sleep curtailment may provide a better understanding of its acute, direct and immediate effects. The advantage of this method is that it can be performed in a laboratory as a buffet after sleep curtailment, which provides more reliable intake data than self‐reported intake in a free‐living environment and is less susceptible to reporting errors. At a buffet, it is important to consider carefully which foods will be offered. If testing for homeostatic regulation of intake, ideally, a typical breakfast should be provided to reduce the potential impact of factors such as food unfamiliarity, palatability and desirability. However, if the effects of sleep curtailment on intake are hypothesised to be mediated through the hedonic appetite and food reward pathways, assessing the intake of highly palatable foods (e.g., (Yang et al. 2019)), is a stronger methodological choice.

In contrast to the one‐meal approach, if a study aims to understand the potentially longer‐lasting effects of sleep curtailment, assessing dietary intake over a day or longer will be necessary. Lengthy studies may not be feasible in a laboratory setting; a discussion on using laboratory vs. free‐living environments is provided in the next paragraph. Measuring intake over several meals will offer valuable insights on whether higher dietary intake in the first meal post‐sleep curtailment (if any) can lead to a persistent positive energy balance or induce compensatory mechanisms where higher intake in the first meal is offset in subsequent meals. In the multiple‐meal assessment approach, it is important to note that day‐to‐day intake is highly variable and compensation in energy intake to restore energy balance can lag by 3 to 6 days (Champagne et al. 2013), which may explain why some studies in this review did not see an effect of sleep on food intake. Thus, dietary assessment over several days will be required to fully assess the full impact of sleep curtailment on intake.

We also noted that dietary intake in these studies was assessed in a lab (using fixed meals or ad libitum) or self‐reported in a free‐living environment or a combination of both. Laboratory environments increase accuracy by reducing reporting bias and error but do not reflect intake in a real‐life setting, resulting in lower ecological validity. This ecological validity problem can be overcome by measuring intake in a free‐living environment. However, self‐reported intake is susceptible to reporting errors, leading to less reliable and potentially larger variations in dietary intake data, which can reduce the effect size of the study and increase the sample size required. In summary, the selection of dietary assessment methods should consider the research questions and aims.

5. Recommendations for Future Research

Guided by a framework (Figure 1) and based on available studies, the hypothesis that sleep curtailment stimulates appetite and motivation to eat, which leads to subsequent higher dietary intake, cannot be confirmed due to several limitations. Based on what has been presented so far, recommendations for future research in this area include:

1. The use of a solid framework to guide study design. Some key considerations include the severity of sleep curtailment (how many hours/night), length of curtailment (how many days) and structure of curtailment (advanced wake time vs. delayed bedtime).

2. Selecting methods that best capture the effects of interest. For example, the selection of appetite tools that capture homeostatic and/or hedonic appetite or the selection of food type based on the hypothesised homeostatic vs. hedonic appetite regulation pathways, which will guide how dietary intake should be analysed or reported. For example, if hedonic appetite is the focus, reporting intake of sugar and salt and the intake of palatable foods in the diet may be particularly relevant

3. Careful consideration of the research setting. If the research question explores immediate effects on intake, a laboratory setting is ideal. However, if the study focuses on long‐term effects, a free‐living environment may be necessary to increase study feasibility and ecological validity, but careful selection of tools to capture dietary intake in a free‐living environment will be crucial.

6. Conclusion

Given the limited number of studies involving different sleep curtailment protocols, frequent use of small sample sizes and varied approaches to measure appetite and dietary intake, definitive conclusions about whether sleep curtailment alters appetite, motivation to eat and dietary intake cannot be drawn at this time. More carefully designed studies, which consider the points above, are needed to improve our knowledge and understanding of this topic.

Author Contributions

Sze‐Yen Tan: conceptualization, methodology, data curation, supervision, writing – original draft, writing – review and editing, formal analysis, visualization, project administration. Isabella Emillya Tjahjono: methodology, data curation, writing – review and editing. Ilili Feyesa: methodology, data curation, writing – review and editing. Jeew Hettiarachchi: methodology, data curation, writing review and editing. Nahyun Kim: methodology, data curation, writing – review and editing. Reagan Pennycuff: methodology, data curation, writing – review and editing. Amani Qawasmeh: methodology, data curation, writing – review and editing. Robin M. Tucker: conceptualization, methodology, data curation, supervision, writing – review and editing, writing – original draft, formal analysis, visualization.

Funding

Amani Qawasmeh was supported by the USDA National Institute of Food and Agriculture (Award No. 2024‐38420‐41519) and Robin M. Tucker by the USDA National Institute of Food and Agriculture (Hatch #1012976).

Ethics Statement

The authors have nothing to report.

Consent

The authors have nothing to report.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Table S1: Systematic literature search strategy.

Table S2: Summary of findings from randomised, crossover studies (n = 11) included in this review.

Data Availability Statement

Data sharing not applicable to this article as no datasets were generated or analysed during the current study.