Time-restricted eating and its impact on body fat and metabolism in overweight and obese women

This systematic review and meta-analysis adhered to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines (23), and its protocol is registered on PROSPERO under the number CRD42024595472 (Appendix 1).

We systematically searched eight electronic databases (PubMed, Embase, Web of Science, Cochrane Library, CNKI, WanFang, VIP, and CBM) from inception through August 11, 2024. The search strategy aimed to identify all published RCTs evaluating the efficacy of TRE (≤12-h eating windows) for improving body composition (primary outcome) and metabolic parameters (secondary outcomes) in adult women (≥18 years) with overweight and obesity (BMI ≥ 25 kg/m²). Search terms were systematically developed using the PICO framework: (1) population (e.g., "obesity" "overweight"), (2) intervention (e.g., "time-restricted eating" "intermittent fasting" "TRE"), (3) outcomes (e.g., "weight loss" "body fat"), and (4) study design (e.g., "randomized controlled trial," "RCT"). We employed a combination of controlled vocabulary (MeSH/Emtree terms) and free-text terms across title/abstract/keyword fields, with language restrictions limited to English and Chinese. The complete search strategy for database is provided in Supplementary Table S1. To ensure comprehensive coverage, the reference lists of identified publications were manually screened to locate studies eligible for inclusion (24).

Inclusion and exclusion criteria are shown in Table 1. Only language (English and Chinese) were applied as restrictions to the search.

Two reviewers (ZXT and CSY) evaluated the RoB using Version 2 of the Cochrane risk-of-bias tool (RoB 2) (25). The assessment covered domains including random sequence generation, allocation concealment, blinding of participants, providers and outcome assessment, incomplete outcome data, and selective outcome reporting. Adherence issues were considered under RoB 2 (deviations from intended interventions). Every domain was determined to be of high, moderate, or low RoB. Disagreements were resolved by consensus between CSY and ZXT; if consensus could not be reached, a third reviewer (LHT) adjudicated the final judgment.

The Grading of Recommendations, Assessment, Development and Evaluation approach (GRADE) was employed to assess the certainty of the evidence (26). If sufficient publications were identified (n ≥ 10), the funnel-plot (visually asymmetry or not) with Egger's regression test (p < 0.05 indicates the presence of publication bias) was conducted to test publication bias (27).

The following details were extracted: study characteristics consisting of first author, country, year of publication, study design; demographic characteristics of participants: gender, age, sample size; study design including diet plan, intervention mode and period, additional interventions; outcomes such as weight change, BMI and assessment method; comparators; results of pre–post data, means and standard deviations of targeted outcomes.

We separately performed pairwise meta-analyses for each of the primary outcome measures using Stata 17. Weighted mean difference (WMD) was used to establish the effect sizes of TRE compared to the usual care control. Cochrane Q-test and Higgins and Green's I² test were used to test heterogeneity. A p-value less than 0.05 for Cochrane Q-test or an I² statistic higher than 50% would indicate the presence of significant heterogeneity. Random-effect analysis would be applied when substantial heterogeneity existed among included studies (28).

Study characteristics and outcome data were systematically summarized in tables. The primary effect measure was weighted mean difference (WMD) with 95% confidence intervals (CI) for continuous outcomes.

Our systematic search identified 4,482 records. After removing 1,410 duplicates, we screened 3,072 titles/abstracts, excluding 2,928 irrelevant studies. Full-text review of 144 articles excluded 131 for: ineligible interventions (n = 10), wrong settings (n = 58), and unavailable outcome data (n = 63).

Thirteen RCTs (n = 612 participants) met all inclusion criteria and provided sufficient data for WMD calculations. The selection process followed PRISMA guidelines (Figure 1), with independent dual-reviewer screening. Study characteristics are summarized in Table 2.

Our systematic review identified 13 randomized controlled trials (RCTs) with a total of 612 participants (intervention: n = 315; control: n = 297), all providing complete outcome data. Two studies employed three-arm designs: Cienfuegos (29) compared 4-h TRE and 6-h TRE against a shared blank control, and Queiroz (30) compared early TRE and delayed TRE against a shared CR control; these designs yielded 15 pairwise comparisons in total. For synthesis, analyses were stratified by caloric-restriction (CR) status; the dataset comprised seven comparisons of TRE + CR vs. CR and eight comparisons of ad libitum TRE vs. blank control. In multi-arm trials, the shared control was split equally between comparisons to avoid double-counting.

Results concerning the risk of bias in each domain are shown in Figures 2, 3. Two reviewers (ZXT and CSY) evaluated the RoB using Version 2 of the Cochrane risk-of-bias tool (RoB 2) (25). Most of the studies were considered to carry moderate risk (Supplementary Table S2). One exception was rated as carrying a high risk of bias. The Physiotherapy Evidence Database (PEDro) scale further confirmed study quality, with all included trials scoring ≥ 5 (Supplemental Table S3). For publication bias assessment, funnel plot analysis and Egger's test showed no significant asymmetry (Supplemental Figure S1).

We performed a systematic meta-analysis examining 15 distinct outcome measures across four physiological domains: body composition, lipid metabolism, glucose metabolism, and blood pressure in the study participants.

Obesity elevates mortality risks associated with various diseases and increases the likelihood of developing multiple comorbidities. Our findings demonstrate that TRE shows superior efficacy in weight regulation compared to a regular diet among overweight and obese women, the pooled effect aligns with recent meta-analyses showing modest losses, likely reflecting spontaneous reductions in energy intake rather than meal timing under isocaloric conditions (42). Animal studies by Chaix et al. (43, 44) have demonstrated that TRE prevents and reverses adverse metabolic outcomes induced by various nutritional challenges, including obesogenic diets high in fat and sucrose. Compared to high-fat diet-fed mice, TRE-treated mice demonstrated significant reductions in obesity indices and hepatic steatosis, along with improved glucose tolerance and lowered cholesterol levels. These metabolic alterations may indicate enhanced homeostatic regulation across multiple tissue systems. In the general population, daily eating patterns typically span 15 h or longer. The desynchronization between circadian biology and behavioral patterns, particularly food consumption misaligned with endogenous circadian phases, has been identified as a key determinant of obesity and metabolic disorder risks (45). TRE facilitates circadian rhythm realignment through regulated eating-fasting cycles and avoidance of nocturnal caloric intake (46). Furthermore, human participants under TRE protocols have been observed to voluntarily reduce their caloric intake (47).

A key aspect of this study is the subgroup analysis of TRE variants based on CR status. TRE protocols are generally classified as "ad libitum" or "prescribed" (48). "Ad libitum" TRE allows unrestricted food consumption without caloric restriction (CR) during specified feeding windows. In contrast, prescribed TRE entails adherence to specific guidelines regarding food selection or caloric intake during feeding windows. Subgroup analysis demonstrated that TRE alone showed significant weight-loss effects compared to blank controls, whereas the combination of TRE with CR showed no statistically significant difference compared to CR alone. This suggests that TRE's metabolic effects may not surpass those of daily CR in obese individuals (49), with CR accounting for the majority of benefits observed in time-restricted feeding protocols. This interpretation is supported by findings from isocaloric trials, which report no significant difference in weight loss between TRE and traditional calorie-restricted diets when total energy intake is matched (50). These findings highlight the importance of considering distinct characteristics across TRE methodologies. Future research should prioritize standardization of controlled dietary interventions to enable direct comparisons and establish more conclusive findings (48).

TRE demonstrates efficacy in reducing insulin levels among women with overweight or obesity. As a primary metabolic hormone secreted by pancreatic β-cells, insulin primarily regulates glucose homeostasis by promoting cellular glucose uptake and glycogen synthesis. Insulin resistance, characterized by diminished sensitivity to insulin's metabolic actions, is mediated by genetic predisposition and environmental determinants. This metabolic dysfunction constitutes a principal risk factor for type 2 diabetes mellitus, hypertension, dyslipidemia, and atherosclerotic cardiovascular pathologies (51). In our meta-analysis, TRE lowered fasting insulin and HOMA-IR, in line with prior reports (52–54). Mechanistically, constraining the eating window reduces the number and duration of insulinogenic exposures and limits late-evening intake, thereby avoiding the melatonin–dinner mismatch and blunted β-cell responsiveness (55, 56). Shorter eating hours also reduce snacking opportunities; in practice, ad libitum TRE often produces modest spontaneous energy-intake reductions, further decreasing insulin demand (42). Over weeks, prolonged nightly fasting increases fatty-acid oxidation/ketogenesis and may enhance hepatic insulin signaling and insulin clearance, changes consistent with the observed reductions in fasting insulin (57, 58). Previous investigations into prolonged fasting protocols have documented weight reduction, enhanced insulin sensitivity, improved sleep parameters, and attenuated inflammatory responses (37, 59–62). This interpretation is consistent with recent syntheses attributing early metabolic gains to longer fasting-induced energy deficits and circadian alignment rather than timing alone under isocaloric prescriptions (42).

While weight loss remains the primary intervention target for overweight and obese individuals, concomitant body composition changes merit equal attention. Existing evidence indicates that daily CR-induced weight loss comprises approximately 75–80% fat mass reduction and 20–25% FFM loss (63). As a key determinant of basal metabolic rate, FFM plays crucial roles in metabolic regulation, skeletal integrity maintenance, and functional capacity preservation (64). FFM reduction may accelerate age-related strength decline in older women. Moreover, CR-induced weight loss may reduce both resting metabolic rate (RMR) and sympathetic nervous system (SNS) activity, potentially predisposing women to weight regain (65). Our findings reveal that weight loss observed during TRE interventions did not induce additional reductions in fat-free mass or lean body mass among female participants. This finding aligns with previous observations in healthy male cohorts. In this protocol, participants maintained daily 16-h fasting windows while continuing regular resistance training. The intervention resulted in preserved lean body mass and maximal strength alongside body fat reduction in male TRE participants (66). Within the included studies, only one participant discontinued due to inability to adhere to the prescribed feeding window (37). Four trials (29, 30, 33, 34) documented mild transient adverse events, including dizziness, headaches, nausea, and diarrhea. These symptoms typically occurred during the initial intervention phase and resolved spontaneously over time. Collectively, these findings suggest superior compliance and safety profiles of TRE compared to CR interventions.

Our findings indicate that TRE significantly improves insulin levels in overweight and obese women, whereas no significant alterations were observed in blood pressure, glucose metabolism, or lipid profiles. Consistent with these observations, clinical evidence for lipid outcomes in women remains inconclusive, with contradictory findings across trials (67). Notably, experimental evidence demonstrating metabolic benefits predominantly originates from male rodent models (68, 69) or small-scale human clinical trials (70). Taken together, these observations suggest that not all TRE schedules are physiologically equivalent (71, 72). Population data also indicate a non-linear association between nocturnal fasting duration and cardiometabolic indicators: both shorter (<10.0 h) and longer (>14.1 h) fasting durations were independently associated with higher age-related markers in NHANES (73). This schedule-dependence underscores the need to delineate the timing, duration, and stability of the eating window when evaluating metabolic endpoints (55, 74).

These findings imply that the health impacts of TRE's fasting window may involve complex mechanisms requiring further investigation. Future research should prioritize large-scale clinical studies with rigorous designs to objectively determine TRE's effects on glucose metabolism, lipid profiles, and blood pressure regulation.

This systematic review specifically focused on TRE as a distinct dietary intervention and restricted inclusion to overweight and obese female populations, thereby enhancing the clinical relevance and sex-specific interpretability of the findings. By separately analyzing anthropometric and metabolic parameters, and employing standardized tools for quality assessment and evidence grading, the study provides a methodologically robust synthesis of TRE's effects in this demographic. Nonetheless, several limitations should be acknowledged that may influence the generalizability and interpretation of the findings. First, the relatively small number of eligible trials—together with our eligibility criterion restricting inclusion to women-only cohorts or mixed-sex cohorts with ≥85% female participants to preserve analytic focus—resulted in a limited total sample size; accordingly, the findings are primarily applicable to women. Second, the inherent design characteristics of the included studies precluded implementation of blinding procedures. Third, substantial heterogeneity in outcome measurements across primary studies and the limited number of randomized controlled trials reporting secondary outcomes precluded quantitative assessment of publication bias through funnel plot analyses for most endpoints. Collectively, these limitations underscore the necessity for methodologically robust studies with larger sample sizes and extended follow-up periods to comprehensively evaluate TRE interventions in female populations. We also acknowledge that heterogeneity in TRE protocols, such as differences in feeding window duration, timing, and caloric restriction, limited our ability to perform subgroup analyses. We emphasize the need for future trials to directly compare different TRE regimens in women.

Most outcomes had low heterogeneity (I² < 25%). Where ≥10 trials were available, funnel plots were roughly symmetric and Egger's tests were non-significant (Supplementary Figure S1), though limited study numbers mean small-study/publication bias cannot be excluded. We encourage precise TRE reporting—clock-defined daily window (start/end, length), caloric strategy, adherence with monitoring, co-interventions/comparators, and standardized outcomes—to improve inclusion and comparability across trials.