Systematic Review and Meta-analysis of Randomized Clinical Trials Comparing Time-Restricted Eating With and Without Caloric Restriction for Weight Loss

Abstract

Context

Although it is well established that caloric restriction (CR) is the primary driver of weight loss, circadian-driven metabolic benefits have been recognized as possibly enhancing the effects of CR. Time-restricted eating (TRE) has emerged as a promising approach in this context.

Objective

We conducted a systematic review and meta-analysis to compare the effects of TRE with isocaloric diet controls (analysis 1) and non-isocaloric controls (analysis 2) on anthropometric and body-composition parameters in adults with overweight or obesity.

Data Sources

A search was carried out in the Medline, LILACS, Embase, and CENTRAL databases using Medical Subject Heading (MeSH) and similar terms such as “Obesity,” “Obesity, Abdominal,” “Time-restricted eating,” “Body weight,” “Changes in body weight,” and others.

Data Extraction

We included 30 studies involving a total of 1341 participants. Studies were screened based on titles and abstracts followed by full-text reading, and data were extracted from eligible studies using a pre-established form. All these steps were performed by 2 authors independently and blinded, with discrepancies resolved by a third author.

Data Analysis

The results of main findings revealed that, in studies using non-isocaloric controls, the TRE group showed significant reductions in body weight (BW) (mean difference [MD]: –2.82 kg; 95% CI: –3.49, –2.15), fat mass (FM) (MD: –1.36 kg; 95% CI: –2.09, –0.63), and fat-free mass (FFM) (MD: –0.86 kg; 95% CI: –1.23, –0.49). In studies that used isocaloric control strategies, the TRE group showed significant reductions in BW (MD: –1.46 kg; 95% CI: –2.65, –0.26), FM (MD: –1.50 kg; 95% CI: –2.77, –0.24), and FFM (MD: –0.41 kg; 95% CI: –0.79, –0. 03).

Conclusion

TRE yields favorable anthropometric and clinical outcomes, even when intake is isocaloric between the intervention and control groups. This result suggests that circadian effects may enhance the impact of CR on excess weight.

Systematic Review Registration

PROSPERO registration no. CRD42022301594.

INTRODUCTION

The global prevalence of overweight and obesity has escalated into a significant public health concern. Over the last 50 years, rates of obesity have nearly doubled in 73 countries worldwide.¹ This alarming trend has resulted in approximately 40% of the adult population being classified as overweight and an additional 10% to 15% in the obesity category.² Numerous studies have demonstrated that obesity is linked to significant risk factors for a myriad of diseases,³ including various other chronic noncommunicable conditions.^4–7 Consequently, reducing body weight (BW) among those who are overweight or obese, and preventing individuals with adequate weight from becoming overweight, have now taken on a heightened sense of urgency in public health.⁸

Caloric restriction (CR) is considered the standard treatment for addressing overweight and obesity, typically resulting in modest short-term weight loss (WL) (5%–10%) within 26 weeks.⁹ Unfortunately, adherence to CR decreases significantly over time,¹⁰ and many individuals regain significant weight within 1 year.^3,10,11 It is already established that no single dietary approach will result in WL for all individuals,¹¹ and the best approach for a particular individual is the one they can adhere to over the long term.^3,9,12,13 In this context, intermittent fasting (IF), a dietary approach involving cyclic fasting and eating periods, has emerged as an innovative and viable strategy to mitigate the progression of obesity and address metabolic disruptions.^14–16 Among the different types of IF is time-restricted eating (TRE)¹⁷, which involves fasting for 12 to 21 hours daily without voluntary CR, although caloric reduction often occurs inadvertently.¹⁸

Time-restricted eating has gained attention as a simple and appealing lifestyle intervention due to its ease of implementation and adherence.^17,19,20 Several studies highlight the potential benefits of TRE, including weight reduction²¹; improved insulin sensitivity; reduced blood glucose, cholesterol, and triglyceride levels²²; and improved quality of life.²³ While these findings are promising, further research is necessary to confirm their validity and determine their broader applicability. Notably, animal studies consistently demonstrate significant positive outcomes of TRE,²⁴ yet the evidence in humans remains less conclusive.²⁵ Several clinical studies have reported positive metabolic changes, such as weight reduction in adults, while others have not produced comparable results.^26–29

A crucial aspect of assessing variability in the benefits of TRE involves investigating whether these benefits result from involuntary CR due to the shortened eating window, from improvements in metabolic function associated with circadian rhythms, or from a combination of both. While other studies often evaluated TRE more generally, few have systematically analyzed the effects of TRE by comparing isocaloric and non-isocaloric groups.²¹ This approach is essential to determine whether the effects are solely due to CR or if circadian factors also play a role. In this context, the aim of this study was to separately investigate the impact of TRE compared with isocaloric diet controls and TRE compared with non-isocaloric diet controls on anthropometric and body-composition parameters in adults with overweight or obesity. We hypothesized that, even when TRE is compared with isocaloric strategies, it could still yield significant results in BW and body composition, suggesting the potential role of circadian metabolic advantages.

METHODS

This systematic review was conducted in accordance the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines³⁰ (Figure S1), and followed the recommendations outlined in the Cochrane Handbook for Systematic Reviews of Interventions.³¹ The protocol for this review was preregistered with PROSPERO (registration number: CRD42022301594). The search strategy and inclusion criteria were developed based only on randomized clinical trials (RCTs) and those meeting the PICOS (Population, Intervention, Comparison, Outcomes, and Study design) criteria (Table 1).

Search Strategy and Study Selection

A systematic literature search was performed in multiple databases, including LILACs (via Virtual Health Library [VHL]), Medline (via PubMed), Embase (via Elsevier), and CENTRAL (via the Cochrane Library) from February 2022 to April 2022 (first selection), followed by an additional search for articles in February 2023. In addition, a search was conducted in clinical trial registries (ClinicalTrials.gov), and gray literature sources were explored through Open Gray (http://opengray.eu) and Google Scholar. A manual search was also carried out in the reference lists of included studies and other systematic reviews. No language or publication date restrictions were applied. The search strategy used various key words related to but not limited to “Obesity” (Medical Subject Heading [MeSH]), “Obesity, Abdominal” (MeSH), “Time-restricted feeding” (MeSH), “Time-restricted eating” (MeSH), “Body Weight” (MeSH), “Body Weight Changes” (MeSH), and others (Table S1).

All studies obtained from the initial search were imported into the RAYYAN platform³² for initial screening. Two reviewers (D.F.-A. and G.P.T.) screened the studies based on titles and abstracts, independently and blinded. Any conflicts were resolved by a third reviewer (C.A.C.). Subsequently, full-text articles for potentially eligible studies were retrieved and independently reviewed by 2 authors (D.F.-A. and G.P.T.). Any discrepancies were resolved through consultation with a third author (C.A.C.). The inclusion criteria for the studies encompassed the following aspects: (1) RCTs; (2) intervention groups practicing TRE; (3) control group during the intervention period instructed to follow an isocaloric diet compared with the intervention group; (4) participants aged 18 years or older; and (5) participants classified with overweight or obesity (body mass index [BMI] >25 kg/m²), with or without any chronic diseases.

To classify the studies as isocaloric or non-isocaloric, we considered both the methodology described in the studies and a detailed analysis of the caloric intake data provided. A study was classified as isocaloric if it explicitly stated that caloric intake was equivalent (ie, with no statistically significant difference) between the groups (intervention and control) or, even without such a statement, presented data showing similar caloric intake between the groups. Conversely, studies were classified as non-isocaloric if they did not mention caloric intake equivalence or if the data presented indicated significant differences in caloric intake between the groups. In cases where caloric intake data were not explicitly reported in the articles, we contacted the authors via email to obtain this information.

Data Extraction

Data extraction from the included studies was independently performed by 2 authors (D.F.-A. and G.P.T.) using an adapted data-collection form based on the Cochrane model.³³ The following data were extracted from each study: authors and year of publication; information regarding the intervention, comparison, and duration of the intervention; baseline characteristics of the participants; and results. Missing data were requested from the study authors by email.

Risk-of-Bias Assessment

The risk-of-bias assessment was performed using the Cochrane Risk of Bias table³⁴ through the Cochrane Review Manager software version 5.4.³³ Two authors (D.F.-A. and G.P.T.) were responsible for screening the included studies and evaluating the risk of bias. This assessment encompassed various domains, including sequence generation, allocation concealment, participant and outcome blinding, incomplete outcome data, selective reporting, and other potential sources of bias. The overall quality of bias was independently judged by 2 authors (D.F.-A. and G.P.T.) and discrepancies in judgment were resolved by a third author (C.A.C.). The methodological rigor of each domain was judged as follows: low risk (no identified issues), unclear risk (insufficient information for assessment), or high risk of bias (relevant bias identified).

Assessment of Evidence Quality and Strength of Recommendations

The Grading of Recommendations Assessment, Development and Evaluation (GRADE)³⁵ approach was used to analyze the quality of evidence and assess the strength of recommendations related to the primary outcomes of this study. The GRADE approach allows for a detailed analysis of each study included in the meta-analysis, considering a series of criteria such as study design, consistency of results, precision of estimates, publication bias, and other relevant considerations. Based on this analysis, we were able to classify the recommendations as high, moderate, low, and very low (Table S2).

Data Synthesis

We used Review Manager version 5.4³³ to conduct 2 separate meta-analyses based on interventions and control characteristics. Both analyses compared the TRE group with a control group. In isocaloric TRE studies, both the intervention and control groups followed an isocaloric diet, meaning that calorie consumption was statistically similar between the groups. In non-isocaloric TRE studies, the TRE group’s calorie intake may have been lower than the control group’s due to the reduced eating window. To classify articles as isocaloric or non-isocaloric, we used the information provided in the methods and results sections, including whether energy intake results were presented for both groups (intervention and control) and whether the article described total daily caloric intake as isocaloric or non-isocaloric. When these data were unavailable, we contacted the authors by email to request this. Studies that did not provide the information or for which the authors did not respond were not included in the review.

For continuous data, the results are presented as weighted mean differences (WMDs) with corresponding 95% CIs. A random-effects model was used for meta-analysis due to anticipated clinical and methodological heterogeneity between studies. Forest plots were used to assess the overall effects of both interventions (with isocaloric strategies and non-isocaloric strategies). The presence of heterogeneity was evaluated using the I² statistic, where I² >50% indicated significant heterogeneity among the included studies.^36,37 Additionally, a risk-of-bias chart was generated using Review Manager version 5.4³³ to visually assess potential bias between the studies. We conducted subgroup analysis to investigate the sources of heterogeneity, but these did not reveal any significant differences.

RESULTS

Characteristics of Included Studies

Figure 1 shows a flowchart of the entire study selection process. A total of 8026 studies were included after an initial search of electronic databases and manual search. The studies were selected using Rayyan software³² by 2 independent authors, blinded, and who screened the studies by reading of the title and abstract according to the inclusion criteria. After removing 2306 duplicates, 5730 records were available for screening. Following review of the titles and abstracts, we excluded 5607 studies, resulting in 123 studies. After reading the full texts, 93 articles were excluded if they did not meet the inclusion criteria, resulting in a total of 30 articles being included. Among the studies included, 15 had isocaloric strategies in the control group (isocaloric TRE) and 15 studies did not have isocaloric strategies in the control group (non-isocaloric TRE).

A total of 1341 participants were included in this study. The largest study recruited 118 individuals,¹⁸ while the smallest recruited 18 individuals.³⁸ The duration of interventions varied significantly, with the longest study spanning 12 months³⁹ and the shortest intervention lasting 13 days.³⁸ We performed subgroup analysis using the median intervention duration in both meta-analyses (with and without isocaloric strategies). The results of these analyses were consistent, suggesting that the variation in intervention duration did not significantly affect the outcomes. Table 2 provides a comprehensive view of the incorporated studies, highlighting their respective interventions and primary outcomes.

Of the 30 studies included in this study, 16 studies were not included in the meta-analysis due to incompatible data.^{28,29,40–48,50–53} Of the studies selected for conducting the meta-analysis, 9 studies had participants who followed an isocaloric dietary strategy in both the control group and the intervention group (TRE group).^{18,39,54–60} In 5 studies, participants in the intervention group (TRE) followed their usual diet without specific guidance on nutritional quality, macronutrient composition, or caloric intake, resulting in variations in energy intake between the groups.^16,61–64

Risk of Bias in Included Studies

The risk of bias for the RCTs is shown in Figure 2. Two studies identified in this analysis did not provide information on randomization procedures. Allocation concealment was not mentioned in 8 studies.^{18,40,45,47,48,52,54,65} Blinding of participants was not possible due to the nature of the study, but in 9 included studies, blinding of participants was not mentioned.^{23,29,38,39,43,55,56,61,64} Four studies did not mention investigator masking and statistical analysis of the data.^38,39,55,56 One study was conducted virtually and was included as another source of bias.⁵⁷

We conducted sensitivity analyses to assess the robustness of the findings to potential biases arising from studies with a high risk of bias for randomization, allocation concealment, incomplete outcome data, and selective reporting. Studies presenting these biases were excluded, and the meta-analysis was subsequently repeated. The overall direction and significance of the results remained consistent.

Weight Loss

Non-Isocaloric Strategies

Five studies evaluating WL using non-isocaloric strategies were included in the analysis.^16,61–64 A significant reduction in WL favoring the TRE group was observed when compared with the control group (MD: –2.82 kg; 95% CI: –3.49 to –2.15; GRADE: low certainty of evidence, I² = 97%) (Figure 3).

Ten studies were not included in the meta-analysis due to incompatible data.^{28,29,41–44,46,65–67} Among them, the studies by Chow et al,⁴³ Bantle et al,⁴¹ Crose et al,⁴⁴ Lobene et al,⁶⁷ Papageorgiou et al,²⁸ Gabel et al,^46,65 Chair et al,⁴² and Domaszewski et al⁶⁶ reported significant WL in the TRE groups, while Phillips et al²⁹ found no significant difference in WL between the TRE and control groups.

Isocaloric Strategies

Nine studies using isocaloric strategies provided data on WL.^{18,39,54–60} A significant reduction in WL favoring TRE was observed compared with the control group (MD: –1.46 kg; 95% CI: –2.65 to –0.26; GRADE: moderate certainty of evidence; I² = 90%) (Figure 3).

Six studies were excluded from the meta-analysis due to incompatible data.^{40,47,48,51–53} Among them, Kotarsky et al,⁴⁷ Amodio et al,⁴⁰ and Lin et al⁴⁸ reported significantly higher WL in the TRE groups, while Parr et al,⁵¹ Tinsley et al,⁵³ and Steger et al⁵² found no significant difference in WL between the TRE and control groups.

Body Mass Index

Non-Isocaloric Strategies

Two studies using non-isocaloric strategies^16,64 provided data on BMI reduction. Both studies reported no significant differences between the TRE group and the control group (MD: –0.63 kg/m²; 95% CI: –1.81 to 0.56; GRADE: low certainty of evidence; I² = 96%) (Figure 4A).

Thirteen studies were not included in the meta-analysis due to incompatible data.^{23,28,29,41–43,45,46,61–63,65,67} Among them, Chair et al⁴² reported more significant reductions in BMI in the TRE group compared with the control group, while Phillips et al²⁹ found no significant difference in BMI reduction between the TRE and control groups. BMI results were not reported in the remaining studies.

Isocaloric Strategies

Four studies using isocaloric strategies^18,39,59,60 evaluated BMI. In these studies, no significant differences were observed between the TRE group and the control group (MD: –0.13 kg/m²; 95% CI: –0.28 to 0.01; GRADE: low certainty of evidence; I² = 9%), indicating a more pronounced reduction in the TRE group (Figure 4A).

Eleven studies were not included in the meta-analysis due to incompatible data.^{40,47,48,51–58} However, Kotarsky et al⁴⁷ demonstrated a greater increase in BMI for the TRE group (1%) compared with the control group (0.1%). In other studies, BMI results were not reported.

Waist Circumference

Non-Isocaloric Strategies

Figure 4B shows 1 study using non-isocaloric strategies⁶⁴ that evaluated WC. No significant MD was observed between the TRE and the control groups (MD: 0.10 cm; 95% CI: –1.24 to 1.44; GRADE: low certainty of evidence).

Sixteen studies were not included in the meta-analysis due to incompatible data.^{16,23,28,29,41–43,45,46,61–63,65,67} Among them, Chair et al⁴² reported more significant reductions in WC in the TRF group compared with the control group, while Phillips et al²⁹ found no significant difference in WC reduction between the TRE and control groups. The WC results were not reported in the remaining studies.

Isocaloric Strategies

In relation to studies that used isocaloric strategies, there were no significant MDs between the TRE group and control group (MD: –0.59 cm; 95% CI: –2.23 to 1.05; GRADE: low certainty of evidence; I² = 30%)^18,39,56,60 (Figure 4B).

Eleven studies were not presented in the meta-analysis due to incompatible data.^{40,47,48,51–55,57–59} Among them, Kotarsky et al,⁴⁷ Fagundes et al,⁵⁵ and Lin et al⁴⁸ reported significant reductions in WC after the intervention, while Steger et al⁵⁸ found no statistically significant difference in WC reduction. In other studies, WC results were not reported.

Percentage of Body Fat

Non-Isocaloric Strategies

It was not possible to perform a meta-analysis with the percentage body fat (%BF) data due to the incompatibility of data from all studies. In the study conducted by Isenmann et al,⁶⁴ the TRF group exhibited a decrease in %BF from 22.8 ± 6.4 kg to 19.4 ± 6.0 kg (Δ: 3.4 ± 1.6 kg; 14.99%; P < .000, r = 0.548). In the study by Chow et al,⁴³ the TRE group did not show significant reductions compared with control group. In other studies, %BF results were not reported.

Isocaloric Strategies

No significant differences in %BF were observed between the TRE group and the control group with isocaloric strategies (MD: –0.58%; 95% CI: –1.31% to 0.16%; GRADE: low certainty of evidence; I² = 51%)^18,39,60 (Figure 5A).

Twelve studies were not included in the meta-analysis due to incompatible data.^{40,47,48,51–59} Among them, Fagundes et al,⁵⁵ Tinsley et al,⁵³ and Kotarsky et al⁴⁷ reported changes in %BF, with Fagundes et al⁵⁵ observing a reduction in %BF in both groups, while Tinsley et al⁵³ found a reduction in the TRE group. However, Parr et al⁵¹ found a greater decrease in %BF in the control group compared with the TRE group, and Kotarsky et al⁴⁷ found no significant differences in %BF reduction between groups.

Fat Mass

Non-Isocaloric Strategies

Three studies^62–64 using non-isocaloric strategies reported data on fat mass (FM), and a significant difference was observed favoring the TRE group compared with the control group (MD: –1.36 kg; 95% CI: –2.09 to –0.63; GRADE: low certainty of evidence; I² = 97%) (Figure 5B).

Twelve studies were not presented in the meta-analysis due to incompatible data.^{16,23,28,29,41–43,45,46,61,65,67} Chow et al⁴³ demonstrated that the TRE group experienced a greater reduction in FM (–4.0%; SD: 2.9%). In other studies, FM results were not reported.

Isocaloric Strategies

Studies evaluating FM in participants using isocaloric strategies also revealed significant differences favoring the TRE group compared with the control group (MD: –1.50 kg; 95% CI: –2.77 to –0.24; GRADE: low certainty of evidence; I² = 69%)^18,53,56,58 (Figure 5B).

Eleven studies were not presented in the meta-analysis due to incompatible data.^{39,40,47,48,51,52,54,55,57,59,60} Among them, Kotarsky et al⁴⁷ reported nearly 3 times higher FM loss in the TRE group compared with the control group, while Parr et al⁵¹ observed a greater FM reduction in the control group compared with the TRE group. Lin et al⁴⁸ found significant FM reductions in both groups, while Steger et al⁵⁸ observed a greater FM reduction in the TRE group, although the results did not reach statistical significance. Fat mass results were not reported in the remaining studies.

Fat-Free Mass

Non-Isocaloric Strategies

Two studies^62,63 depicted in Figure 5C, which used non-isocaloric strategies, demonstrated significant differences in favor of the TRE group compared with control group regarding fat-free mass (FFM) (MD: –0.86 kg; 95% CI: –1.23 to –0.49; GRADE: low certainty of evidence; I² = 95%).

Thirteen studies were not presented in the meta-analysis due to incompatible data.^{16,23,28,29,42,43,45,46,61,64,65,67,68} Among them, Chow et al⁴³ reported a greater reduction in FFM in the TRE group, while Lobene et al⁶⁷ observed a reduction in FFM in the TRE group compared with pre-intervention. Isenmann et al⁶⁴ found no significant changes in FFM in either group, and Gabel et al^46,65 reported no significant differences between the TRE and control groups. The FFM results were not reported in the remaining studies.

Isocaloric Strategies

Similarly, studies using isocaloric strategies^18,56,58 to evaluate FFM also demonstrated significant differences favoring the TRE group when compared with the control group (MD: –0.41 kg; 95% CI: –0.79 to –0.03; GRADE: low certainty of evidence; I² = 19%) (Figure 5C).

Twelve studies were not presented in the meta-analysis due to incompatible data.^{38–40,47,48,52–55,57,59,60} Among them, Kotarsky et al⁴⁷ reported an increase in FFM in the TRE group (2.4%) compared with the control group (1.2%), while Parr et al⁵¹ observed a greater reduction in FFM in the TRE group compared with the control group. Fagundes et al⁵⁵ also found a reduction in FFM in both groups, with 40.7% in the TRE group and 31.8% in the non-TRE group. The FFM results were not reported in the remaining studies.

High heterogeneity was observed in the analyses of BW with isocaloric and non-isocaloric strategies, BMI with non-isocaloric strategies, FM (kg) with isocaloric and non-isocaloric strategies, and FFM with non-isocaloric strategies.

Secondary Risk Factors

Three studies^16,62,63 using non-isocaloric strategies suggested a potential reduction in fasting blood glucose levels in the TRE group (MD: –8.35 mg/dL; 95% CI: –13.76 to –2.93). Three studies that evaluated non-isocaloric strategies^16,62,63 evaluated reduction in insulin levels and significant differences were observed favoring the TRE group compared with the control group (MD: –6.29 mg/dL; 95% CI: –7.90 to –4.68; I² = 95%). Additionally, 1 study¹⁶ with non-isocaloric strategies suggested a reduction in total cholesterol in the TRE group (MD: –3.06 mg/dL; 95% CI: –3.09 to –3.03). In studies that used non-isocaloric strategies,^16,62,63 a notable difference was observed favoring the TRE group compared with the control group regarding triglyceride (TG) levels (MD: –2.97 mg/dL; 95% CI: –5.40 to –0.54; I² = 73%). Two studies^62,63 using non-isocaloric strategies suggested significant reductions in both diastolic blood pressure (DBP) (MD: –5.39 mmHg; 95% CI: –6.30 to –4.47) and systolic blood pressure (SBP) (MD: –8.40 mmHg; 95% CI: –9.54 to –7.27) in the TRE group (see Figures S2–S4 in the Supporting Information online).

DISCUSSION

The present study evaluated the relationship between TRE and anthropometric and body-composition parameters in adults with overweight or obesity, focusing exclusively on RCTs to isolate the effects of circadian alignment and the benefits associated with CR. The analyses revealed that studies evaluating TRE strategies with non-isocaloric control groups—where the TRE group may have experienced greater CR due to the reduced eating window—showed, as expected, significant reductions in several anthropometric and metabolic variables, such as BW, FM, FFM, fasting blood glucose, insulin, total cholesterol, TG, SBP, and DBP, compared with the control group. However, in studies using TRE strategies with isocaloric controls, significant reductions were observed primarily in anthropometric variables such as BW, FM, and FFM. Notably, no significant differences were found between TRE strategies with isocaloric and non-isocaloric controls in terms of BMI, WC, %BF, glycated hemoglobin (HbA1c), Homeostatic Model Assessment for Insulin Resistance (HOMA-IR), or high-density-lipoprotein (HDL) and low-density-lipoprotein (LDL) cholesterol in the TRE group.

Reducing energy intake is a widely adopted approach recognized for inducing WL through a negative caloric deficit^9,12 and appears to yield greater effectiveness when pursued gradually with consistency, encompassing sustainable lifestyle changes.¹² The positive effect is attributed to the inhibition of anabolic processes, enhancing mitochondrial energy metabolism, and alterations in substrate utilization.^69–71 These mechanisms decrease reliance on glucose metabolism while promoting increased oxidation of fatty acids.^72,73 Given the potential of TRE to either induce or not induce caloric deficits, we deemed it relevant to conduct 2 meta-analyses based on caloric content (with isocaloric and non-isocaloric strategies compared with their respective controls) to discern whether the alterations in body composition, glucose levels, lipid profiles, and blood pressure could be attributed to the TRE strategy alone or jointly to a reduction in energy intake. From this perspective, as expected, we found in the 2 analyses carried out that TRE promoted numerous metabolic and anthropometric benefits. However, we also found that TRE, compared with the control group with the same caloric intake, still yields significant anthropometric effects in individuals with overweight or obesity. These findings should be considered significant as they attribute an additional benefit to TRE in the treatment of excess weight, a chronic condition that affects the global population and for which available treatments remain insufficient.⁷⁴

Among dietary therapeutic strategies, TRE has garnered attention for its potential health benefits, including enhancements in metabolic parameters.^75,76 This phenomenon arises from the circadian benefits of earlier food intake during the day and limiting nocturnal consumption,⁷⁶ given that late-day periods appear to lead to greater insulin resistance⁷⁷ and lipid disturbances⁷⁸ compared with the morning time period. Furthermore, TRE strategies appear to offer a potentially cost-effective and sustainable lifestyle in which daily calorie intake is confined to a consistent time window without explicit attempts to alter diet composition or reduce calories.^24,26,79 Despite the growing number of clinical trials on this topic,^{18,57,75,79,80} it remains uncertain whether any potential benefits of TRE arise from the CR derived from its practice or the circadian benefits of reducing nocturnal energy intake, or both. In our study, metabolic improvements were evident only when TRE effectively induced CR in most analysis, suggesting that improvement in the metabolic circadian component alone may not be sufficient if not accompanied by energy restriction.

It is important to highlight that TRE is not a suitable strategy for everyone. Some individuals may encounter difficulties in adhering to this practice, with the main barriers including inadequate diet quality during the eating window, hunger, sluggishness, misalignment of TRE with 24-hour activity behaviors, and challenges with self-monitoring.⁸¹ It is estimated that adherence to the protocol that exceeds 70% is necessary to observe beneficial effects.⁶⁴ Therefore, it is always advisable for a qualified healthcare professional to evaluate the patient before initiating any protocol.

The present review does have certain limitations that need to be addressed. First, the number of studies per outcome included in the meta-analyses was limited, thus reducing statistical power. Consequently, we emphasize the importance of conducting further high-quality studies, to better observe the effectiveness of TRE on anthropometric and metabolic variables. Additionally, high heterogeneity was found in some analyses, highlighting the differences among the studies. However, this bias is inherent and commonly encountered in meta-analyses. Finally, the assessment of dietary intake in the included studies relied on subjective methods. While these are widely used and have scientific validity, they have known limitations, including potential recall bias and underreporting. Readers should take note of these limitations when assessing the practical or clinical impact of TRE for WL. On a positive note, we underscore the thoroughness of the literature search conducted and the fact that this analysis included only RCTs, ensuring high methodological rigor.

CONCLUSION

In conclusion, the results presented in this research highlight the efficacy of TRE in achieving significant reductions in several anthropometric variables. These results indicate that TRE leads to favorable anthropometric and clinical outcomes. Similar benefits were observed even when TRE did not produce a greater caloric deficit compared with the control group—that is, when intake was isocaloric between the intervention and control groups. This suggests that circadian benefits may augment the effects of CR in the treatment of overweight.

Author Contributions

D.F.-A., K.C.G., and C.A.C. participated in the planning, interpretation of results, and writing of the manuscript. D.F.-A. and K.C.G. performed the statistical analysis. D.F.-A., G.P.T., K.C.G., and C.A.C. participated in the interpretation of results, the statistical analysis, and writing of the manuscript.

Supplementary Material

Supplementary Material is available at Nutrition Reviews online.

Funding

C.A.C. is a CNPq fellow (no. 401761/2022–3) and expresses gratitude for this support. D.F.-A. received a Capes scholarship and is grateful for the support.

Conflicts of Interest

None declared.

REFERENCES