Meals

Obesity and metabolic disorders remain major global health concerns, traditionally attributed to excessive caloric intake and poor diet quality. Recent studies emphasize that the timing of meals plays a crucial role in determining metabolic health. This review explores chrononutrition, a growing field that examines how food intake patterns interact with endogenous circadian rhythms to influence energy balance, glucose and lipid metabolism, and cardiometabolic risk. The circadian system, which includes a central clock in the suprachiasmatic nucleus and peripheral clocks in metabolic tissues, regulates physiological functions on a 24 h cycle. While light entrains the central clock, feeding schedules act as key synchronizers for peripheral clocks. Disrupting this alignment-common in modern lifestyles involving shift work or late-night eating-can impair hormonal rhythms, reduce insulin sensitivity, and promote adiposity. Evidence from clinical and preclinical studies suggests that early time-restricted eating, where food intake is confined to the morning or early afternoon, offers significant benefits for weight control, glycemic regulation, lipid profiles, and mitochondrial efficiency, even in the absence of caloric restriction. These effects are particularly relevant for populations vulnerable to circadian disruption, such as adolescents, older adults, and night-shift workers. In conclusion, aligning food intake with circadian biology represents a promising, low-cost, and modifiable strategy to improve metabolic outcomes. Integrating chrononutrition into clinical and public health strategies may enhance dietary adherence and treatment efficacy. Future large-scale studies are needed to define optimal eating windows, assess long-term sustainability, and establish population-specific chrononutritional guidelines.

ImportanceMeal timing strategies, such as time-restricted eating (TRE), reducing meal frequency, or altering calorie distribution across the day, have gained interest for their potential to enhance weight loss and metabolic health, particularly in managing chronic diseases, yet their long-term benefits are not known.ObjectiveTo evaluate the association between meal timing strategies (≥12 weeks) and anthropometric and metabolic indicators.Data sourcesMedline, Embase, CINAHL, and Cochrane CENTRAL were searched from inception to October 17, 2023.Study selectionRandomized clinical trials, regardless of language and publication date, involving adults 18 years and older, evaluating within-day meal timing patterns for 12 or more weeks, and reporting anthropometric measures were included. Studies were excluded if participants had eating disorders, prior significant weight change, underwent bariatric surgery, were pregnant, or if controlled variables differed between groups.Data extraction and synthesisStudy quality was determined via Risk of Bias 2.0 tool. Data were extracted independently by multiple reviewers. Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines were used. Meta-analysis was performed using random-effects model on pooled continuous outcomes with 2 or more studies.Main outcome and measuresWeight change in kilograms, reported as between-group mean difference with 95% CIs.ResultsSixty-nine reports of 29 randomized clinical trials including 2485 individuals (1703 [69%] female; mean [SD] age, 44 [9.5] years; and mean [SD] body mass index, 33 [3.5]) were included. Study interventions included TRE (17 studies), meal frequency (8 studies), and calorie distribution (4 studies). There were some concerns of risk of bias for 7 studies and high concerns for 22 studies. Statistically significant weight change was observed in TRE when compared with control (-1.37 kg; 95% CI, -1.99 to -0.75 kg). Lower meal frequency and earlier caloric distribution were also both associated with greater change (-1.85 kg; 95% CI, -3.55 to -0.13 kg; and -1.75 kg; 95% CI, -2.37 to -1.13 kg, respectively).Conclusions and relevanceThe findings of this meta-analysis suggest that TRE, lower meal frequency, and earlier caloric distribution in the day may reduce weight compared with standard care and/or nutritional advice; however, the effect sizes found were small and of uncertain clinical importance. High heterogeneity and risk of bias among included studies led to concerns about the certainty of the underpinning evidence. Further research, including trials with larger sample sizes, standardized interventions with prescribed or matched energy intake, and longer follow-up, are needed.

BackgroundA novel 'whole day' approach that could motivate the public to be more physically active is Snacktivity™. The Snacktivity™ approach encourages individuals to accumulate 150 min of physical activity in short 2-5-min 'snacks' of moderate-vigorous intensity physical activity (MVPA) throughout the day/week.MethodA randomised controlled trial to assess the feasibility/acceptability of a Snacktivity™ intervention and trial processes was conducted. The trial aimed to recruit 80 physically inactive adults from healthcare services and via social media. Participants were randomised to the Snacktivity™ intervention or usual care and followed up at 12 weeks. The intervention was predominately delivered by health professionals within consultations. Assessment of whether the Snacktivity™ intervention and trial methods were acceptable to participants, adherence to Snacktivity™ (assessed by Fitbit) and physical activity (assessed by accelerometer), and retention were considered according to traffic light stop-go progression criteria (green-amber-red).ResultsSeventy-two participants (n = 37 Snacktivity™ intervention; n = 35 usual care) were recruited across 14 months (72/80, 90%, (green) 95% CI: 83% to 97%). Snacktivity™ adherence was achieved in 12/37 participants (32%, (red) 95% CI: 17% to 48%). Physical activity adherence was achieved in 17/37 participants (46%, (amber) 95% CI: 30% to 62%). Seven participants (10%, (green) 95% CI: 3% to 17%) withdrew from follow-up and 25/72 (35%, (amber) 95% CI: 24% to 46%) had no accelerometer data at follow-up (retention).ConclusionThe Snacktivity™ intervention may be feasible and acceptable to implement. Findings can inform subsequent research that seeks to investigate whether Snacktivity™ based approaches are effective in promoting physical activity in the population.Trial registrationISRCTN: 64851242. Registration date: 31/01/21.

Associations between stress, emotions and unhealthy eating have been reported, yet findings remain inconsistent. Stress eating and emotional eating have frequently been used interchangeably despite potential differences regarding physiological and psychological explanations. To aid in disentangling the shared and unique effects of stressors and emotions, we examined their associations with distinct aspects of eating behaviour (food craving, quantity, healthiness and snacking) in daily life in an experience-sampling study. Participants (N = 64) responded to six daily smartphone prompts over 4 weeks, reporting stressors, multidimensional emotional states (valence, arousal, calmness) and eating behaviour. Bayesian multilevel models revealed that general stressors were unrelated to snacking (OR = 1.07, 90% CI = [0.87, 1.32]), but episodes of time pressure increased snacking likelihood (OR = 1.34, 90% CI = [1.01, 1.75]) while being associated with lower food quantity (B = -2.45, 90% CI = [-4.07, -0.82]). Arousal was associated with more food intake (B = 0.04, 90% CI = [0.001, 0.087]), while there was no other emotional state-eating association. Together, these results indicate that changes in snacking behaviour are more strongly linked to specific situational constraints, such as time pressure, than to momentary emotional fluctuations. Emotional eating, operationalised as emotion-driven snacking independent of stressors, received little support in this sample. These findings suggest that interventions may benefit from targeting situational constraints, such as time pressure.