The Role of Cheat Meals in Dieting: A Scoping Review of Physiological and Psychological Responses

Abstract

“Cheat” meals are characterized as a pause from energy restriction to allow relaxed ad libitum energy intake in a short period of time, usually as a single meal, a single day, or meals that spread across multiple days, such as over the weekend. Incorporating cheat meals has become a popular strategy in the diet and fitness communities, with individuals often indulging in large meals containing energy-dense foods. Proponents of this strategy typically suggest that intermittent periods of pauses in prolonged dieting might serve as a “mental break,” “boost metabolism,” or enhance exercise performance. This review aims to examine existing literature on cheat meals, exploring both physiological and psychological responses. A systematic search was conducted in 5 databases using all available records until October 2, 2024. A total of 8 articles were selected for detailed analysis. Currently, the available data provided some evidence regarding the ability of short, intermittent bouts of ad libitum dietary intake to facilitate effective weight reduction; however, the evidence on the retention of lean mass, the attenuation of metabolic adaptation, or the improvement in exercise performance during weight reduction was mixed. When framed as a goal-directed behavior, positive influences of ad libitum intake on eating behaviors, such as reducing feelings of hunger and enhancing satisfaction, were notable. However, the analysis revealed that framing cheat meals as contradictory to one’s goals or normalizing cheat meals as a form of reward for committing to a strict dietary regimen could be associated with the manifestation of eating disorder behaviors. Therefore, while cheat meals might offer physiological and/or psychological benefits in some circumstances or applications, they also pose risks of fostering unhealthy eating patterns. Considering the rising prevalence of cheat meals, future research is strongly warranted to unravel the complex physiological and psychological ramifications of cheat meals, to equip healthcare and fitness professionals in devising a safe and effective diet strategy for sustainable weight loss.

INTRODUCTION

In recent years, the concept of incorporating “cheat” meals into a diet has gained traction in the fitness communities. These intermittent break periods over the course of a diet, characterized by a more relaxed energy intake, are believed to potentially “boost metabolism” and offer a “mental break.”^1–3 Although scientific validation of these benefits is lacking, the practice has become increasingly popular. Celebrities with muscular and toned physiques frequently share photos of their cheat meals on social media, often resulting in viral posts. According to a thematic content analysis by Pila et al,⁴ the social media presence of cheat meals is evidenced by over 1.6 million images tagged “#cheatmeal” posted on the social media platform Instagram (Meta Platforms, USA) as of October of 2016. The same search returned 4.3 million posts when repeated on December 8, 2024. Additionally, a study involving over 2000 Canadian adolescents and young adults found that more than half reported having cheat meals at a frequency of more than once per week over 1 year.⁵

Continuous energy restriction (CER) has been used traditionally as a weight-reduction strategy, typically by reducing 15%–60% of daily energy intake from energy balance.⁶ It has, however, been well documented that CER could lead to a cascade of adverse effects to the human body, both physically and mentally.^7,8 The physiological effects include a series of homeostatic alterations in circulatory hormones, mitochondrial efficiency, and energy expenditure, in which the human body adapts towards underfeeding as a survival mechanism during famine.^8,9 During CER, the reduction in resting metabolic rate (RMR) is greater than that expected based solely on changes in body composition.¹⁰ This adaptive mechanism termed “metabolic adaptation” often leads to weight reaching a plateau despite adhering to a CER regimen.¹⁰ On the other hand, the psychological effects of CER include increased feelings of hunger and reduced satisfaction, increased irritability, mood swings, emotional instability, and preoccupation with food, often leading to attrition and nonadherence.^11,12

To mitigate the negative effects of CER, strategies to implement intermittent periods of breaks in dieting, such as diet breaks, refeeds, and cheat meals, have emerged as a viable strategy in weight-reduction regimens.² These intermittent breaks are characterized as periods of time that allow a more relaxed energy intake over the course of dieting. As reviewed by Roberts et al,³ there are important distinctions among common approaches to intermittent dieting. A diet break is a continuous period of time, typically lasting from 4 days to several weeks, in which energy intake is increased to restore neutral energy balance with specific macro-/micronutrient targets. A refeed is typically a 1- to 3-day period in which energy intake is increased to achieve neutral energy balance or a small (5%–10%) energy surplus with specific macro-/micronutrient targets. A cheat meal is a single ad libitum meal without specific energy or macro-/micronutrient targets. A cheat day is a similar strategy, with the only distinction being that the ad libitum approach is applied to the full day rather than a single meal. These strategies have been discussed extensively in previous literature^2,13 and are summarized in Figure 1. Systematic reviews on diet breaks and refeeds have shown that incorporating these breaks led to similar effects on body-composition changes as with CER.^13,14 However, there is a significantly smaller compensatory reduction in RMR as compared with CER, which suggests a lesser extent of metabolic adaptation.¹³ Some studies on diet breaks and refeeds have also shown improved psychological well-being with temporarily increased energy intake.^15,16

Figure 1.

Characteristics of Different Types of Intermittent Dieting

Compared with a diet break or a refeed, a cheat meal has 1 unique characteristic—that is, it involves a brief period of unrestricted eating without a specific energy or macronutrient target, which could lead to different physiological and psychological responses. It remains unclear whether consuming food ad libitum without a specific energy target might undo weight-reduction efforts from energy restriction as compared with diet breaks and refeeds, which usually involve set energy targets, or if a short duration of breaks might exhibit similar effects on attenuating metabolic adaptation as the week-long diet breaks. Currently, cheat meals are popular among the fitness community, and some evidence suggests its potential benefits in preserving lean mass and enhancing exercise performance.^17,18 Additionally, existing literature on diet breaks and refeeds indicates beneficial impacts on dietary behavior, such as reduced hunger and enhanced satisfaction.¹³ However, several psychological studies focused specifically on cheat meals have raised concerns that episodes of unrestricted eating could resemble symptoms of binge-eating disorder.^4,19 Therefore, it remains uncertain whether short and relaxed cheat meals might produce similar effects on eating behaviors when comparing with a diet break or refeed.

Despite the growing interest in cheat meals, to our knowledge a comprehensive review of the existing literature regarding the effects of cheat meals in dieting is currently lacking. To date, systematic reviews have predominantly examined diet breaks and refeeds,^13,14 while only a limited number of narrative reviews have addressed cheat meals.^2,3 Additionally, these narrative reviews have primarily looked at various intermittent dieting strategies without specifically analyzing cheat meals. Moreover, they did not include a systematic search and predominantly concentrated on the application of these dieting strategies among physique athletes. Yet, exploring the application of cheat meals within the general population is essential, given that these strategies are also widely adopted by non-athletes.^4,20 Furthermore, these reviews did not thoroughly explore the psychological outcomes associated with cheat meals. At present, there are only a small number of original studies available. While these studies yielded mixed and inconsistent results regarding the effects of cheat meals on physiological outcomes, such as metabolic adaptation, lean mass retention, exercise performance, and eating behaviors, they offer insights into the potential benefits and drawbacks of incorporating cheat meals into weight-reduction regimens. In light of the above, this scoping review aims to investigate the physiological and psychological effects of cheat meals. By providing a comprehensive analysis, the findings of this review would be valuable to healthcare and fitness professionals in devising a safe and effective diet strategy for sustainable weight loss, and cautiously advising on the practice of cheat meals in case of any potential harm they may bring.

METHODS

Search Strategy

This scoping review was conducted in accordance with the latest Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) 2018 checklist.²¹ Electronic database searches were performed in PubMed, Web of Science, Scopus, SPORTDiscus, and PsycINFO, utilizing all available records up to October 2, 2024. A literature search was also performed in the online registry (ClinicalTrials.gov). The search terms covered the areas of intermittent energy restriction, ad libitum refeed, RMR, body composition, intuitive eating, and binge eating. Detailed search strategies for databases are provided in Appendix S1 (see the Supporting Information online).

Study Eligibility

The Population, Concept, and Context (PCC) criteria are shown in Table 1. Various terms other than “cheat meal(s)” (such as “ad libitum feeding,” “self-selecting diet,” and “diet-breaking behavior”) have been used to describe the concept of a cheat meal. To be included in this review, eligible physiology-related studies needed to meet the following criteria: (1) clinical trials involving participants on an energy-restricted diet with short bouts of ad libitum intake, (2) the energy-restricted phase constituted the majority of the week, (3) the dietary intervention lasted at least 4 weeks (as this is the minimum time frame for any observable meaningful body-composition changes in typical intervention studies), and (4) body-composition outcomes were measured. Eligible psychology-related studies had to meet the following criterion: described the psychological issues associated with using cheat meals in the context of restricted dietary regimens. Studies involving intermittent breaks lasting for 1 week or longer and/or breaks with planned energy intake targets of neutral energy balance or only slightly above were excluded from this review, as they exhibit characteristics of “diet break” or “refeed” (instead of cheat meal) as defined by the classification scheme proposed by Escalante et al.² Furthermore, it is important to note that intermittent breaks, although described as intermittent periods of energy restriction, are conceptually different from intermittent fasting (IF). The former focuses on taking breaks from energy restriction, whereas the latter focuses on incorporating fasting episodes or severe energy restriction as a means to create energy deficit for weight reduction. Given the conceptual difference, studies that primarily focused on IF concepts, such as the 5:2 diet, time-restricted feeding, and alternate-day fasting, were also excluded.

Table 1.

PCC Criteria of Inclusion of Studies

Parameter	Criterion
Population	No exclusion criteria were applied to participants’ baseline characteristics. Individuals of all ages were included.
Concept	Cheat meal(s) is defined as short bouts of ad libitum intake that act as intermittent break periods during energy restriction. Outcomes include BM, FFM, RMR, eating behaviors, attrition rate, and psychological outcomes.
Context	Human clinical trials in English were selected.

Abbreviations: BM, body mass; FFM, fat-free mass; RMR, resting metabolic rate.

Data Extraction and Bias Assessment

Two reviewers (J.H.T. and E.T.-C.P.) independently screened the titles, abstracts, and full texts of the identified studies using predetermined criteria. Reviewer disagreements were resolved through consensus or arbitration with a third reviewer (F.S.). Two data-extraction tables were developed (Tables  2 and  3). Table 2 includes the extracted data of physiology-related studies, detailing the lead author, country, year of publication, population characteristics, intervention protocols, duration, attrition rate, and main findings. Table 3 includes the extracted data from psychology-related studies, detailing the lead author, country, year of publication, population characteristics, observed phenomena, and psychological issues identified. The risk-of-bias assessment was conducted using the Cochrane risk-of-bias tool for randomized trials (RoB 2)²² with the following domain included: randomization process, deviations from intended interventions, missing outcome data, measurement of the outcome, and selection of the reported results.

Table 2.

Summary of Physiology-Related Studies Meeting the Inclusion Criteria

Study (year), country	Population	Age, y	Group	Sample size, n	Intervention	Total duration, wk	Attrition rate, %	Main findings
Davoodi et al (2014),23 Iran	74 Overweight/obese females	37.1 ± 5.7	Ad-I	37	Consisted of three 2-wk phases with 11 d of ER (subtracted 45% of baseline EI) followed by 3 d of self-selected diet	6	15.7	BM of Ad-I and CER decreased significantly with no between-group differences RMR tended to remain unchanged in Ad-I Feeling of hunger decreased and satisfaction increased in Ad-I after 4 wk into intervention
		35.2 ± 4.8	CER	37	Prescribed low-calorie diet (subtracted 55% of baseline EI)	6	36.8
de Moraes et al (2024),18 Brazil	14 Male bodybuilders	20.6 ± 3.1	Ad-I	14	Consumed the allocated ER diet (<40% of habitual intake) for 5 d, followed by 2 d of refeed (included 2 ad libitum meals)	4	0	BM decreased with most participants having reduced BF and preserved/gained LM Amount of EI during Ad-I is inversely related to satiety, confidence in hunger and satiety cues, IES-2 total score, congruence in food-body choice dimensions Emotional coping is inversely related to IES-2 total score and amount of EI during Ad-I
Moura et al (2021),17 Brazil	11 Male bodybuilders	28.4 ± 2.3	Ad-I (moderate ER)	6	Consumed the allocated ER diet (≥60% of habitual intake) for 5 d, followed by 2 d of refeed (included 2 ad libitum meals)	4	0	Both groups had a reduction in BM and BF while maintaining FFM Blood CK and VAS values for muscle soreness were reduced only in Ad-I group with severe ER
			Ad-I (severe ER)	5	Consumed the allocated ER diet (<60% of habitual intake) for 5 d, followed by 2 d of refeed (included 2 ad libitum meals)	4	0
Xu et al (2021),24 China	26 Healthy adults (22 females)	34.3 ± 5.1	Ad-I	12	Consumed low daily EI (∼800 kcal) for 1-4 d, followed by 1 cheat day	4	33.3	BM of Ad-I and CER decreased significantly with no between-group differences RMR had a significant decrease in Ad-I but not in CER; however, there were no between-group differences
		29.0 ± 6.4	CER	14	Consumed ER of 500 kcal daily (excluded EAT)	4	28.6

Abbreviations: Ad-I, ad libitum intake; BF, body fat; BM, body mass; CER, continuous energy restriction; CK, creatine kinase; EAT, exercise activity thermogenesis; EI, energy intake; ER, energy restriction; FFM, fat-free mass; IES-2, Intuitive Eating Scale-2; LM, lean mass; RMR, resting metabolic rate; RT, resistance training; VAS, visual analog scale.

Table 3.

Summary of Psychology-Related Studies Meeting the Inclusion Criteria

Study (year), country	Population	Age, y	Observed phenomena	Psychological issues identified
Coelho do Vale et al (2016),25 Portugal (study 2)	36 University students and staff (29 females)	24 ± 7.44	N/A	Weight reduction requires sustained behaviors for a prolonged period Rather than a straight goal pursuit, a planned goal deviation may improve self-regulatory ability, increase motivation, boost experience of positive affect, and increase flexibility while not negatively influencing the desired weight-reduction outcomes
Ganson et al (2022),5 Canada	2717 Canadian adolescents and young adults (1476 females, 1060 males, 181 transgender)	16-30	60.9% Men, 53.7% women, and 52.5% transgender participants engaged in cheat meals in the past 12 mo >1 Cheat meal per week for 12 mo Cheat meals mostly contained 1000-1499 kcal Men have a higher frequency of opting for high-protein foods during cheat meals, whereas women and transgender participants opt for sweet foods	Associated with patterns of eating disorder behaviors and psychopathology that are displayed in the presentation of binge-eating–related behaviors
Murray et al (2018),19 USA	248 Young adults (139 females)	19.29 ± 0.58	89.1% of participants reported engagement in either planned or spontaneous cheat meals	Frequency of cheat meals is positively associated with global eating disorder symptoms and objective binge episodes among men Cheat meals do not resemble loss-of-control eating but are perceived as eating episodes of volitionally letting go of control, predominantly aimed at managing food cravings and assisting adherence to strict dietary regimens Not associated with psychological distress or clinical mental health–related impairment for either gender
Pila et al (2017),4 USA	600 Images with #cheatmeal tag on a social media platform	N/A	Over 1.6 million photos with the tag “cheatmeal” were found on social media Photos displayed energy-dense foods (71.3%) that were of large quantities (54.5%) containing 214 kcal to as much as 9120 kcal   - 60.7% of photos displayed individuals of objectified highly muscular bodies, with 40% of intentional body exposure	A cheat meal with at least 1000 kcal per meal is rated to qualify as an objective binge episode Its characteristics of an immediate compensation post–cheat meal via adherence to strict dietary restrictions and exercise (ie, weightlifting) resemble the symptomatic patterns displayed in bulimia nervosa Exemplifies the normalization and explicit endorsement of overconsumption behavior, which is portrayed as a reward for strict commitment to rigid fitness practices associated with the pursuit of muscularity

Abbreviation: N/A, not applicable.

RESULTS

Study Selection

The search strategy described previously identified 3191 records from electronic databases and 4 records from registers. A total of 1201 duplicate records were removed, and 1990 records were screened. Among all of the screened records, 1894 records were excluded after title and abstract screening due to different topic of interest. Of the 96 remaining records, review articles and studies with experimental protocols that did not match the inclusion criteria of a cheat meal were eliminated by retrieving full texts (Appendix S2). Studies that adopted diet breaks, refeeds, and IF protocols were also excluded. As a result, 4 studies fulfilled the inclusion criteria. In addition, 1 record was retrieved from a website and 3 records were retrieved from citation searching. These records did not appear in the database search due to the use of uncommon key words such as “planned hedonic deviations”, “calorie shifting diet”, and “bodybuilders”. A total of 8 records with 4 physiology-related and 4 psychology-related studies were included in the review (Figure 2).

Figure 2.

Flow Diagram of the Literature Search Process.

Characteristics of the Included Studies

The 4 physiology-related studies are summarized in Table 2.^17,18,23,24 The publication dates were between 2014 and 2024. The total sample sizes of the studies ranged from 11¹⁸ to 74,²³ with a total of 125 participants. One study involved healthy individuals,²⁴ 2 studies involved bodybuilders,^17,18 and 1 study involved individuals who were overweight/obese.²³ One study involved both sexes,²⁴ 2 involved only males,^17,18 and 1 study involved only females.²³ With regard to age range, all 4 studies had relatively young participants aged from 20.6 ± 3.1¹⁸ to 37.1 ± 5.7 years.²³ The studies were conducted in China,²⁴ Brazil,^17,18 and Iran.²³ The dietary intervention of 2 studies compared the incorporation of ad libitum intake with CER^23,24; 1 study compared ad libitum intake with moderate energy restriction (MER) or severe energy restriction (SER)¹⁷; and 1 study did not have a comparison arm.¹⁸ The duration of the studies ranged from 4 to 6 weeks.

The 4 psychology-related studies are summarized in Table 3.^4,5,19,25 The dates of publication were between 2016 and 2022. The total sample sizes of the studies ranged from 36²⁵ to 2717,⁵ with a total of 3065 participants. Four studies involved individuals of both sexes,^4,5,19,25 with 1 study also involving transgender participants.⁵ With regard to age range, the studies had relatively young participants aged from 16 to 30 years.⁵ One study involved 600 social media images.⁴ Studies were conducted in the United States,^4,19 Canada,⁵ and Portugal.²⁵ The studies examined the phenomenon of cheat meals and their underlying psychopathology/psychological issues.

DISCUSSION

To the best of our knowledge, this is the first review investigating the responses of cheat meals during an energy-restricted diet on physiological and psychological aspects of the human body and mind. Key findings from the existing literature suggest that incorporating ad libitum intake during energy restriction results in a significant reduction in body weight. However, the evidence regarding its effects on mitigating metabolic adaptation, preserving lean mass, and enhancing exercise performance remains inconclusive. Furthermore, cheat meals have been associated with positive changes in eating behaviors, such as reduced hunger and increased satiety. This approach, which offers flexibility rather than a rigid dieting regimen, may provide psychological benefits by enhancing motivation, although it could also resemble disordered eating patterns.

Changes in Body Weight

A common concern with incorporating ad libitum feeding episodes, which resemble cheat meals after a period of energy restriction, is whether the unlimited energy intake might overcompensate for the energy deficit created during the energy-restricted period, potentially hindering weight-reduction efficacy or even cause weight gain. Earlier studies on diet breaks and refeeds, which incorporated non–energy-restricted phases maintained at energy balance instead of ad libitum, predictably found significant weight reduction.^16,26 Interestingly, all 4 studies included in our review that incorporated ad libitum intake as an intervention protocol also showed a significant reduction in body weight.^17,18

The study by Davoodi et al²³ used an intermittent energy-restriction protocol alternated between 11 days of energy restriction at 55% of baseline energy intake (1365 ± 214 kcal/d) and 3 days of ad libitum intake and resulted in an increased energy intake at 1971 ± 224 kcal, which remained at an energy deficit compared with the baseline energy intake of 2460 ± 264 kcal. The 2 studies by Moura et al¹⁷ and de Moraes et al¹⁸ involved bodybuilders in preparation for competition. In Moura et al’s study, the 2 days of ad libitum intake led to a 36.8% and 46.3% increase in average daily energy intake as compared with the 5 energy-restricted days for the MER and SER groups, respectively. Despite the increase in energy intake on ad libitum feeding days, the mean energy intakes across the week were 72.9% and 53.4% of habitual energy intake for the MER and SER groups, respectively, which showed that they remained at an energy deficit. The de Moraes et al study,¹⁸ despite the 2 days of ad libitum intake, which led to a 44% increase in average daily energy intake compared with the 5 energy-restricted days, resulted in a 27% weekly energy deficit. Two studies^23,24 comparing the group with ad libitum intake with CER showed no significant differences in the degree of weight loss between the 2 intervention protocols. The study by Xu et al²⁴ showed no significant difference in the total energy deficits achieved between the group with ad libitum intake incorporated once every 1–4 days of energy restriction (<800 kcal) and the CER group at a daily 500-kcal deficit from energy balance, and no significant difference in the degree of weight loss between the 2 groups. As such, despite the heterogeneity among the included studies with various patterns of ad libitum intakes, the incorporation of these breaks with higher energy intake than energy-restricted days during dieting may still incur an overall energy deficit, leading to a significant reduction in body weight.

On the other hand, a previous study that did not adopt the protocol with the intention of weight reduction (therefore excluded from our review) observed only moderate weight loss after 4 weeks of alternating between 4 days of an energy-restricted diet (<600 kcal) and 3 days of ad libitum intake.²⁷ The mean intake on days with unlimited intake increased significantly from week 1 to week 4. We therefore speculate there could be a further increase in energy intake on the ad libitum feeding days if the intervention protocol extended beyond 4 weeks, which may largely reduce the degree of weight loss. One of the popular IF strategies used commonly with the intention of weight reduction is alternate-day fasting, which alternates between fasting days and unrestricted nonfasting days, and resembles a similar duration of ad libitum feeding as described above. It has, however, been shown to be effective in weight reduction as it can lead to a substantial energy deficit over time.²⁸ The findings were in line with existing literature that showed that energy intake during ad libitum feeding episodes was slightly lower than baseline energy intake, thereby creating an overall energy deficit.²⁹ As such, the effectiveness of incorporating ad libitum intake leading to positive body-composition changes might be dependent on whether it is implemented alongside the intention of weight reduction, the frequency and duration of ad libitum intake, and the degree of energy restriction during the energy-restricted phase.

Metabolic Adaptation

During a period of energy restriction, the human body responds to a negative energy balance by upregulating hunger cues and downregulating energy expenditure to defend against weight loss.⁹ The adaptive mechanism is driven by an increase in sympathetic drive and a cascade of hormonal alterations that include a reduction in levels of thyroid hormones, insulin, leptin, and testosterone and an increase in ghrelin and cortisol.² These adaptations potentially lead to weight-loss plateaus by reducing RMR to a greater extent. This has sparked the idea of incorporating “metabolic breaks” during energy-restricted phases, temporarily increasing energy intake to reverse or attenuate these metabolic adaptations.

Our group previously demonstrated in a systematic review and meta-analysis of 7 studies that incorporating intermittent breaks during dieting can potentially mitigate the compensatory reduction in RMR.¹³ In our current review, only 2 studies compared the incorporation of ad libitum feeding episodes with CER and that measured RMR as an outcome.²³ Xu et al²⁴ showed that RMR decreased significantly only in the group with ad libitum intakes but not CER; however, there were nonsignificant between-group differences. On the other hand, Davoodi et al²³ showed that, despite the nonsignificant between-group difference in percentage of weight loss, the reduction in RMR in the CER group was significantly greater. The contradictory results might be due to the heterogeneity of the studies with inconsistencies in the duration of ad libitum intake. Studies have previously shown that suppressed thyroid levels during energy restriction returned to baseline concentrations following a period of 7–10 days of increased energy intake.³⁰ In addition, a few days of energy restriction sufficiently suppressed leptin levels, while a 3-day overfeeding period resulted in a 25% increase in leptin in participants who were previously underfed.³¹ The insignificant findings in the ad-libitum group of Xu et al’s study²⁴ may be attributed to the possibility that the 1-day ad libitum intake might be too short to reverse any hormonal adaptations to elicit imminent mitigation of RMR during energy restriction. As with Davoodi et al’s²³ study, the RMR of the group with ad libitum intake tended to decrease during each 11-day period of energy restriction and then increased with 3 days of ad libitum intake. Overall, the RMR remained unchanged when comparing baseline with post-intervention values. In addition, a previous study that utilized a 2-day refeed suggested potential advantages in lessening the reduction in RMR as compared with CER.²⁶ However, the applicability of this finding has been challenged based on a nuanced critique of the statistical approach used to interpret RMR.³² As such, it is unclear whether there is a potential “metabolic boosting” effect of short ad libitum intake protocols, such as a single cheat day or cheat meal. Further investigation is needed to examine the dose–response relationship of ad libitum intakes (ie, 1 meal per week vs 1–2 days per week), the extent of energy intake (ie, overfeeding vs energy balance), and the potential underlying hormonal responses that may be responsible for producing metabolic attenuation benefits.

The 2 studies included in the review had some limitations. The study by Xu et al²⁴ estimated RMR using a population-based formula—Schofield’s equation—as opposed to measuring RMR using laboratory-based metabolic measurements. This approach posed challenges in accurately reflecting metabolic adaptation through changes in RMR. The study by Davoodi et al²³ had weekly RMR measurements, some of which took place during or shortly after an abrupt increase in energy intake, which may reflect a transient increase in response to short-term increases in energy intake rather than a sustained attenuation of metabolic adaptation. This can have considerable, but transient, impacts on measured RMR.³³ Moreover, the potential for inadequate dietary adherence should be considered in this study. The ad libitum intake group had a higher energy intake per day than the CER group; however, given the lack of substantial differences in baseline characteristics and the modest changes in RMR throughout the 6-week intervention period, it remains unclear how the ad libitum group was able to achieve nominally greater weight loss than the CER group.

Furthermore, this area of research is complicated by the focus on measuring metabolic adaptation mainly through changes in RMR. While RMR is the most feasible component of total daily energy expenditure to measure in such studies, non–exercise-activity thermogenesis may also significantly contribute to adaptations in response to weight-loss interventions.³⁴ Given the small amount of published data in this area, inconsistent findings, and the methodological considerations described above, a definitive conclusion remains elusive.

Lean Mass and Exercise Performance

Among fitness communities that pursue high levels of muscular development, a commonly proposed benefit of cheat meals, which typically involve consuming large amounts of carbohydrates, is to potentially enhance anabolic response and reduce catabolic response when combined with resistance training, thereby preserving lean mass during energy restriction.³⁵ The theory is supported by the underlying physiology pathway, by potentially increasing leptin concentrations, which activate the insulin-mediated Mammalian Target of Rapamycin Complex 1 pathway for enhancing muscle protein synthesis, and reducing cortisol and muscle protein breakdown.³⁶ In the study by Moura et al,¹⁷ which adopted a 2-day carbohydrate ad libitum intake alternated with a 5-day energy restriction protocol for 4 weeks, participants in the MER and SER groups lost 50% and 25% of their weight as fat-free mass, respectively; however, this did not reach statistical significance. A study by de Moraes et al,¹⁸ which followed a comparable intervention protocol, showed that participants lost 48% of their weight as lean body mass and 52% as fat mass simultaneously. These proportions of weight lost as lean mass are not meaningfully dissimilar from typical weight-loss studies,³⁷ although both studies involved individuals actively engaging in resistance training and consuming a high-protein diet. Nonetheless, the findings from these studies are consistent with previous studies, which also focused on resistance-trained individuals and compared the effects of incorporating diet breaks with CER.^15,16 These studies exhibited similar retention in fat-free mass between CER and groups with diet breaks. In contrast, findings from another study involving obese individuals showed a smaller proportion of weight loss as fat-free mass in the group with diet breaks compared with the CER group.³⁸ It is plausible to infer that the contrasting results are related to inherently different starting body composition between resistance-trained and obese individuals.¹⁵ Taken together, there is insufficient evidence to suggest that ad libitum feeding or any type of intermittent breaks during weight loss meaningfully improve lean mass retention in resistance-trained individuals; however, further research is warranted for other population groups.

With regard to exercise performance, acute high-carbohydrate intake is thought to provide temporary benefits on training quality as intramuscular glycogen depletion has previously been shown to impair muscle function.³ However, Moura et al’s study,¹⁷ which examined the effect of a high-carbohydrate, ad libitum intake on the performance of an intensive training protocol (German Volume Training), found that high-carbohydrate, ad libitum intake had no effects on ratings of perceived exertion and total number of repetitions performed when compared with training conducted during the energy-restricted phase. Blood creatine kinase levels and muscle soreness scores were reduced only in the SER group but not the MER group, suggesting that high-carbohydrate, ad libitum intake may help with attenuating the perception of muscle soreness and maintaining performance when energy restriction is severe. These results are in line with a previous study that also found no differences in muscle strength and endurance between groups that utilized diet breaks and CER approaches.³⁹ The minimal effects could be explained by a recent systematic review, which indicated that neither acute carbohydrate feeding nor a high-carbohydrate diet benefits resistance-training performance when compared with low-carbohydrate intake unless training is conducted at higher volumes under a fasted state.⁴⁰ It is therefore speculated that the benefit of intermittent breaks, whether ad libitum or not, is small on exercise performance unless energy restriction is severe and training volume is high.

Eating Behavior and Psychological Responses

Eating Behavior and Adherence

From a physiological perspective, altered appetite sensations during energy restriction could be due to changes in appetite-regulating hormones, including a reduction in satiety hormones (ie, leptin and peptide YY) and an increase in the hunger hormone ghrelin.¹⁵ Incorporating ad libitum intakes may temporarily mitigate these negative effects, potentially by reversing the hormonal adaptations. The study by Davoodi et al²³ found that feelings of hunger were significantly less in the group with ad libitum intake as compared with the CER group towards the end of the weight-loss phase in overweight/obese individuals. Satisfaction also significantly increased among those with ad libitum intake after 4 weeks of the intervention. Similarly, an earlier study on diet breaks also showed that the group with diet breaks had significantly higher satiety and satisfaction than the CER group, along with elevated fasting peptide YY levels.¹⁵ However other appetite-regulating hormones, such as leptin and active ghrelin, did not differ between groups.¹⁵ While the positive changes in appetite sensation are evident in groups with intermittent breaks, future research is needed to confirm the hormonal responses related to ad libitum intakes.

The positive appetite responses potentially led to a lower attrition rate for the group with ad libitum intake (15.7%) as compared with the CER group (36.8%) in the study by Davoodi et al.²³ Studies by Moura et al¹⁷ and de Moraes et al¹⁸ also did not have any dropouts; however, it is worth noting that these 2 studies involved bodybuilders only, who were well-trained individuals with high levels of self-discipline.⁴¹ Although a slightly higher attrition rate in the group with ad libitum intake (33.3%) than that of the CER group (28.6%) was observed in Xu et al’s²⁴ study involving healthy participants, the number of participants who dropped out of the study was the same, and the total sample size was small (n = 26) in this study. Despite the heterogeneity of population types among studies, incorporating ad libitum intakes appears to be a potentially effective strategy for maintaining diet adherence.

Potential Psychological Benefits

From a psychological perspective, periods of ad libitum intake may offer a “mental break” from strict energy restrictions by managing food cravings and social aspects. Both men and women, typically of highly muscular physiques, often engaged in spontaneous or planned cheat meals as a reward for sustaining a commitment to fitness goals.⁴ In addition, individuals on a restrictive diet might face social issues (eg, when eating out with others not on restrictive diets), and can use cheat meals as a means to assimilate with the groups during social activities.⁴² Traditional goal pursuit theory has emphasized the importance of persistence in goal-striving activities and avoiding goal-breaking activities.^25,43 However, the concept of cheat meals challenges the theory as to whether these hedonic goal deviations are beneficial in achieving weight loss as a goal. Coelho do Vale et al²⁵ found that participants with 1 day of increased energy intake per week retained self-regulatory ability levels and motivation to pursue their diet, whereas those without this dietary deviation did not, showing that deviations may increase persistence to achieve goals. As such, flexibility rather than persistence might be of greater importance during dieting. However, deviations should remain small and temporary, and should not override the overarching weight-loss goal.

Potential Risks of Normalizing Cheat Meals

The magnitude and frequency of ad libitum intakes can be too small, so that they do not elicit any psychological benefits as a “mental break,” or can be too large, and so can be detrimental by associating with eating disorders. In our current review, we found 3 studies investigating the possible linkage of cheat meals with disordered eating. Photos with #cheatmeals on social media reveal the presence of large quantities of energy-dense foods, which often show meals containing over 1000 kcal, with some as high as 9000 kcal, which suggest symptoms of eating disorders, particularly when these meals are followed by immediate compensation via adherence to strict dietary restrictions and exercise.^4,5,19 Furthermore, many of these images show individuals of muscular physiques, explicitly endorsing and normalizing cheat meal behaviors that are positively associated with binge episodes.⁴ This normalization can perpetuate cyclical compensatory behaviors aimed at regulating physiques and body weight, potentially leading to long-term psychological effects, including low self-esteem, body image dissatisfaction, and depressive symptoms.⁴⁴

Planned vs Spontaneous Cheat Meals

The psychological mechanisms behind these behaviors are complex and multifaceted. Planned or spontaneous cheat meals may influence distinct forms of disordered eating psychopathology. When cheat meals are planned and perceived as eating episodes of volitionally “letting go” of control that aim at managing food cravings and assisting adherence to a strict diet, rather than a loss of control, they are not associated with psychological distress or clinical mental health–related impairment.¹⁹ This distinction underscores the importance of framing cheat meals as goal-directed behavior rather than behavior that undermines one’s goal. As observed in research on planned hedonic deviation²⁵ or “slack with a cost,”⁴⁵ goal-directed increases in energy intake during weight reduction do not appear to be associated with negative psychological responses. However, deviations perceived as poor compliance or failure from a weight-reduction program have been associated with negative affective responses and subsequent overeating,⁴⁶ consistent with the abstinence violation effect.⁴⁷

In such scenarios, cheat meals may lead to further negative psychological responses and amotivation,⁴⁷ potentially exacerbating disordered eating behaviors. A previous study found that participants’ mood, irritability, and ability to concentrate significantly worsened during a <600-kcal energy-restricted phase, and they experienced a greater drive to consume greater amounts over time during periods of unlimited food consumption.²⁷ This propensity for greater overconsumption may negatively impact dietary adherence, psychological well-being, and long-term body composition. Individuals in weight-loss programs who experience unsatisfactory progress or unintended weight regain due to poor dietary adherence are likely to experience negative psychological symptoms,⁴⁸ further threatening future adherence due to the abstinence violation effect.⁴⁷ The study by de Moraes et al¹⁸ found that heightened perception of hunger and satiety cues, along with intuitive eating practices, reduced aggressive energy consumption during periods of ad libitum intake, even in the presence of emotional coping. In summary, the psychological and behavioral sequelae resulting from unplanned deviations may promote repeating cycles of overeating, negative affect, and restrictive compensatory behaviors, potentially exacerbating disordered eating behaviors and ultimately leading to long-term motivational collapse. Therefore, rather than episodes of mindless eating, incorporating planned cheat meals by appropriately utilizing internal hunger and satiety cues as a strategy to remain motivated during a non–overly restricted diet is preferable to prevent disordered eating.

Balancing Psychological Benefits and Risks

While cheat meals may serve as a psychological break and enhance dietary adherence when framed strategically as goal-directed behaviors, their normalization, when amplified by the prevalent portrayal of cheat meals in social media and association with disordered eating, necessitates careful examination of the underlying psychological mechanisms. Addressing these mechanisms—that is, the role of perceived control, the abstinence violation effect, and the practice of intuitive eating—offers a pathway to mitigating the long-term psychological consequences of cheat meals, hence cultivating sustainable approaches to weight management and mental well-being.

Strengths and Limitations

Our review for the first time provides a comprehensive summary of the evidence surrounding a popular weight-reduction strategy that has not previously been adequately explored. It not only looks at the plausible physiological responses to cheat meals but also psychological perspectives, as they play a significant role in the implementation of cheat meals during a weight-reduction regimen as a whole. Furthermore, we adhered to the latest PRISMA-ScR checklist²¹ to systematically synthesize and report evidence on the effects of cheat meals. We also included a robust search strategy using stringent criteria for study eligibility, which provided new insights into the definition of cheat meals, consolidating physiology-related research that focuses specifically on regimens involving ad libitum intakes that act as intermittent breaks during energy restriction.

Our review also has limitations. First, the number of studies and participants included in physiology-related studies was relatively small. The duration of interventions was also relatively short (ie, 4 to 6 weeks).^17,18,23,24 Additionally, the heterogeneity in study designs, which included varying patterns of cheat meals and different population groups, contributes to the limitations. Risk-of-bias assessment conducted on 2 randomized controlled trials using the Cochrane risk-of-bias tool for randomized trials (RoB 2)²² showed overall “some concerns”²⁴ and “high”²³ risk of bias (Appendix S3). Although a “low” risk of bias was noted for randomization processes, “some concerns” or “high” risk of bias mainly arises from a lack of objective methodological measurement, deviations from intended interventions, missing outcome data with high dropout rates, and selective reporting.^23,24 Other physiology-related studies lacked a comparison arm¹⁸ or control group.¹⁷ Three psychology-related studies were observational cross-sectional studies,^4,5,19 which were considered to be lower in the hierarchy of evidence within the evidence pyramid.⁴⁹ In light of these limitations, the present review highlights the significance of this area of research and warrants future research to fill the knowledge gap. High-quality randomized controlled trials with robust study designs (eg, increasing participant numbers and intervention duration, incorporating control groups, and minimizing biases) are desired as a future research direction. Specifically, examining the individual variability in responses to cheat meals, influenced by factors such as sex, age, metabolic health, modes of physical activity, and cultural influences, could also enhance their individualized application.

Practical Recommendations

Cheat meals, when incorporated in a weight-reduction regimen, should be approached with caution and should not be accompanied by unfounded claims lacking evidence. While there is some evidence regarding their effectiveness on weight reduction and psychological relief, claims regarding their role in mitigating metabolic adaptation and enhancing exercise performance currently lack robust evidence. Instead of engaging in mindless episodes of unplanned eating, cheat meals should be kept minor and occasional throughout the course of a diet regimen. Healthcare and fitness professionals should exercise caution over the incorporation of cheat meals by emphasizing mindful planning and providing individualized guidance, and monitoring for any signs of disordered eating behaviors to minimize potential risks.

CONCLUSION

The incorporation of short bouts of relaxed ad libitum energy intake during prolonged dieting may potentially support effective weight reduction. Nonetheless, the evidence regarding its efficacy in attenuating metabolic adaptation remains inconclusive, possibly due to the short duration of these bouts being insufficient to reverse hormonal adaptations. There is also mixed evidence to substantiate their effectiveness in mitigating the loss of lean mass and preserving exercise performance. Notably, when framed and perceived as a goal-directed behavior, these short breaks may offer psychological relief. However, engaging in mindless episodes of unplanned eating may also resemble patterns of disordered eating behaviors. The present review offers some novel insights into the evidence surrounding this popular strategy, yet further rigorous research is imperative to fill the knowledge gap, particularly in areas of metabolic adaptation, lean mass retention, exercise performance, and psychological outcomes, for the safe and effective incorporation of cheat meals into a weight-reduction regimen.

Author Contributions

J.H.T. and F.S. designed the research. J.H.T. and E.T.-C.P. conducted the searches and completed the screening process. J.H.T. extracted the data, which were verified by E.T.-C.P. and F.S. J.H.T. wrote the manuscript, with critical input from E.T.-C.P., E.T.T., C.Z., S.H.-S.W., and F.S. All authors have read and approved the final manuscript.

Supplementary Material

Supplementary Material is available at Nutrition Reviews online.

Funding

No external funding was received to support this work.

Conflicts of Interest

None declared.

Data availability

Data available upon request.