Achieving synchronization between the central and peripheral body clocks is essential for ensuring optimal metabolic function. Meal timing is an emerging field of research that investigates the influence of eating patterns on our circadian rhythm, metabolism, and overall health. This narrative review examines the relationship between meal timing, circadian rhythm, clock genes, circadian hormones, and metabolic function. It analyzes the existing literature and experimental data to explore the connection between mealtime, circadian rhythms, and metabolic processes. The available evidence highlights the importance of aligning mealtime with the body's natural rhythms to promote metabolic health and prevent metabolic disorders. Specifically, studies show that consuming meals later in the day is associated with an elevated prevalence of metabolic disorders, while early time-restricted eating, such as having an early breakfast and an earlier dinner, improves levels of glucose in the blood and substrate oxidation. Circadian hormones, including cortisol and melatonin, interact with mealtimes and play vital roles in regulating metabolic processes. Cortisol, aligned with dawn in diurnal mammals, activates energy reserves, stimulates appetite, influences clock gene expression, and synchronizes peripheral clocks. Consuming meals during periods of elevated melatonin levels, specifically during the circadian night, has been correlated with potential implications for glucose tolerance. Understanding the mechanisms of central and peripheral clock synchronization, including genetics, interactions with chronotype, sleep duration, and hormonal changes, provides valuable insights for optimizing dietary strategies and timing. This knowledge contributes to improved overall health and well-being by aligning mealtime with the body's natural circadian rhythm.

Globally, increasing rates of obesity are one of the most important health issues. The association between breakfast skipping and body weight is contradictory between cross-sectional and interventional studies. This systematic review and meta-analysis aims to summarize this association based on observational longitudinal studies. We included prospective studies on breakfast skipping and overweight/obesity or weight change in adults. The literature was searched until September 2020 in PubMed and Web of Science. Summary risk ratios (RRs) or β coefficients with a 95% confidence interval (CI), respectively, were estimated in pairwise meta-analyses by applying a random-effects model. In total, nine studies were included in the systematic review and five of them were included in the meta-analyses. The meta-analyses indicated an 11% increased RR for overweight/obesity when breakfast was skipped on ≥3 days per week compared to ≤2 days per week (95% CI: 1.04, 1.19, <i>n</i> = two studies). The meta-analysis on body mass index (BMI) change displayed no difference between breakfast skipping and eating (β = -0.02; 95% CI: -0.05, 0.01; <i>n</i> = two studies). This study provides minimal evidence that breakfast skipping might lead to weight gain and the onset of overweight and obesity.

Current dietary trends show that humans consume up to 40% of their energy intake during the night. Those who habitually eat during the night are observed to have an increased risk of metabolic conditions such as type-2 diabetes and cardiovascular disease. Increasing evidence suggest that a biological consequence of eating during the night is a larger postprandial glucose response, compared to meals eaten earlier in the day. However, findings from individual acute postprandial studies have been inconsistent, due to variations in protocols. Therefore, this review aimed to systematically summarize findings from acute postprandial studies and investigate whether postprandial glucose and insulin response at night differs to during the day in healthy adults. This would indicate a possible physiological mechanism linking habitual nighttime eating and increased risk of metabolic conditions. Seven electronic databases were searched in February 2018. Included studies met the following criteria: had a day-time test between 0700 - 1600h, a nighttime test between 2000 and 0400h, the test meals were identical and consumed by the same participant at both day and night time points, preceded by a 3-h fast (minimum). Primary outcome measures were postprandial glucose and insulin incremental area under the curve (iAUC) or area under the curve (AUC). Studies that reported numerical data were included in the meta-analyses, conducted using Stata statistical software (version 13.0, StataCorp, College Station, TX, USA). For eligible studies that did not report numerical data, their authors' conclusions on the effect of time of day on the primary outcome measures were summarized qualitatively. Full text of 172 articles were assessed for eligibility. Fifteen studies met the eligibility criteria, ten of which were included in the meta-analyses. Meta-analysis for glucose showed a lower postprandial glucose response in the day compared to during the night, after an identical meal (SMD = -1.66; 95% CI, -1.97 to -1.36; <i>p</i> < .001). This was supported by the findings from included studies ineligible for meta-analysis. Meta-analysis also showed a lower postprandial insulin response in the day compared to during the night (SMD = -0.35; 95% CI, -0.63 to -0.06; <i>p</i> = .016). However, findings from included studies ineligible for meta-analysis were inconsistent. Our results suggest poor glucose tolerance at night compared to the day. This may be a contributing factor to the increased risk of metabolic diseases observed in those who habitually eat during the night, such as shift workers.

Time-Restricted Eating is an eating pattern based on the circadian rhythm which limits daily food intake (usually to ≤12 h/day), unique in that no overt restriction is imposed on the quality, nor quantity, of food intake. This paper aimed to examine the effects of two patterns of TRE, traditional TRE, and Ramadan fasting, on two markers of circadian rhythm, cortisol and melatonin. PubMed and Web of Science were searched up to December 2020 for studies examining the effects of time restricted eating on cortisol and melatonin. Fourteen studies met our inclusion criteria. All Ramadan papers found statistically significant decrease in melatonin (<i>p</i> < 0.05) during Ramadan. Two out of the three Ramadan papers noted an abolishing of the circadian rhythm of cortisol (<i>p</i> < 0.05). The non-Ramadan TRE papers did not examine melatonin, and cortisol changes were mixed. In studies comparing TRE to control diets, Stratton et al. found increased cortisol levels in the non-TRE fasting group (<i>p</i> = 0.0018) and McAllister et al. noted no difference. Dinner-skipping resulted in significantly reduced evening cortisol and non-significantly raised morning cortisol. Conversely, breakfast skipping resulted in significantly reduced morning cortisol. This blunting indicates a dysfunctional HPA axis, and may be associated with poor cardio-metabolic outcomes. There is a paucity of research examining the effects of TRE on cortisol and melatonin. The contrasting effect of dinner and breakfast-skipping should be further examined to ascertain whether timing the feeding window indeed has an impact on circadian rhythmicity.

Eating out of phase with the biological clock induces circadian misalignment in peripheral organs and impairs glucose tolerance in preclinical models. Time‐restricted eating (TRE) is a dietary approach that consolidates energy intake to 6 to 10 hours during the biologically active phase of the day, without necessarily altering diet quality and quantity. TRE induces pleiotropic metabolic benefits in mice, flies, and humans. Most studies have initiated TRE early in the biological morning. This perspective discusses the potential challenges in translating early TRE to the community and considers the potential metabolic consequences of delaying TRE.

Background Breakfast consumption is frequently recommended for weight loss and the prevention of obesity. Although breakfast eating has been repeatedly associated with lower BMIs through numerous observational studies and meta‐analyses of observational studies, the causal effects of eating versus skipping breakfast on obesity has not been systematically reviewed. Objective To synthesize available evidence on the effects of eating versus skipping breakfast on anthropometric measures related to weight in randomized controlled trials. Methods Scopus, PsycInfo, CINAHL, Alt‐HealthWatch, and Proquest Global Thesis and Dissertation databases were searched for randomized controlled trials in humans that investigated the effects of breakfast consumption or skipping on weight‐related outcomes. Inclusion criteria were: studies with 72 hours or longer of intervention; reported changes in weight‐related outcomes measured objectively; participants with normal weight or greater; participants without diseases expected to influence weight; and the effects of breakfast eating versus breakfast skipping could be isolated from other treatment components. Titles and abstracts were double coded. Results The search resulted in 4,047 results across databases; 3,255 after duplicates removed; and 3,182 after animal studies were removed using an automated approach. Titles and abstracts from 47 entries were reevaluated for inclusion, with 19 evaluated at the full text level. Two additional articles were identified from alternative sources. Only 6 articles met all criteria, with another 6 papers (possibly only 3 unique studies) seeming to meet all criteria except for reporting of weight. In the 6 papers that met all the criteria, 4 studies were conducted in the US, 2 in the UK; 5 studies in adults, 1 in adolescents (age 18+); study length ranged from 2–16 weeks; 4 parallel arm RCTs, 2 cross‐over RCTs; 3 provided meals and 3 gave recommendations/meal plans; weight‐related outcomes included fat mass, fat mass index, percent fat mass, BMI, fat free mass, waist circumference, waist:hip ratio, and body mass; and the n randomized ranged from 5 to 56 per treatment arm. Of 38 comparisons among breakfast vs skipping on weight‐related outcomes, 2 were significant in favor of a breakfast, and two were significant in favor of skipping. The rest were non‐significant. Conclusions This systematic review does not support the general contention that eating versus skipping breakfast is beneficial for weight‐related outcomes. This does not preclude the possibility that certain types of breakfasts or certain populations may respond positively or negatively to eating vs skipping, or that breakfast may have other health beneficial or detrimental effects. Quantitative synthesis of these results is forthcoming. This systematic review and meta‐analysis was registered at http://www.crd.york.ac.uk/PROSPERO/as CRD42016033290.

<b>Objective:</b> Metabolic syndrome (MetS) represents a growing and significant public health burden worldwide. The evidence regarding whether skipping breakfast affects the development of MetS and its components remains inconsistent and uncertain. This study aimed to synthesize the best available evidence regarding the association between skipping breakfast and the risk of MetS and its components. <b>Methods:</b> This systematic review and meta-analysis was conducted in accordance with the PRISMA 2020 guidelines. We systematically searched the PubMed, Embase, Cochrane Library, and Web of Science databases from inception until May 2025. Two reviewers independently screened titles/abstracts and full texts, extracted data, and assessed the risk of bias. This review included cross-sectional and cohort studies on the association between breakfast skipping and the risk of MetS and its components. <b>Results:</b> Nine studies were included after quality evaluation by NOS. Pooled results from the meta-analysis revealed that skipping breakfast was significantly associated with an increased risk of MetS (OR: 1.10, 95% CI: 1.04-1.17) and its components-namely abdominal obesity (OR = 1.17, 95% CI 1.01-1.34), hypertension (OR: 1.21, 95% CI: 1.10-1.32), hyperlipidemia (OR: 1.13, 95% CI: 1.04-1.23), and hyperglycemia (OR = 1.26, 95% CI: 1.16-1.37). <b>Conclusions:</b> The meta-analysis demonstrated that skipping breakfast was significantly associated with an increased risk of MetS and its key components-abdominal obesity, hypertension, hyperlipidemia, and hyperglycemia. These findings highlight regular breakfast consumption as a potential modifiable factor for preventing and managing MetS and related cardiometabolic diseases.

not significantly related to hypercholesterolemia and coronary heart disease regardless of gender. Nevertheless, skipping breakfast once a week may greatly reduce the benefits of cardio-metabolism. Therefore, public institutions should promote and encourage citizens to cultivate regular daily breakfast habits. Keywords: cardiovascular diseases, meta-analysis, metabolic diseases, mortality 1. Introduction With the acceleration of the pace of modern life, breakfast, which is regarded as an important meal of the day, is being ignored by more and more people, which seemingly as a universal behavior, may have negative effects on your health. [ 1 , 2 ] There are various reasons for skipping breakfast. For office workers, they may not have enough time to eat breakfast. For students, they may lack a good breakfast habit. As for obese patients, they may have a poor appetite or must limit their energy intake. As a matter of fact, regular breakfast habits can keep us energetic in work and study. In addition, eating breakfast can increase satiety, thereby reducing overeating later in the day to restrict weight gain. [ 3 ] Recently, several studies have shown that skipping breakfast increases the risk of obesity, [ 4 ] hypertension, [ 5 ] hypercholesterolemia (HC), [ 6 ] type 2 diabetes mellitus (T2DM), [ 7 ] metabolic syndrome (MetS), [ 8 ] coronary heart disease (CHD), [ 9 ] and cardiovascular mortality (CVM). [ 10 ] Conversely, can regular breakfast habits reduce cardiovascular and metabolic diseases? Most of the previous dietary studies have focused on dietary components and combinations, [ 11 – 14 ] such as dietary fat, cereals, and the Mediterranean diet patterns, while few pay attention to the effects of daily eating behavior on cardiovascular diseases (CVD) and metabolic diseases (MetD). Besides, although a large number of previous studies have revealed the relationship between skipping breakfast and diabetes, most of them were cross-sectional ones. [ 14 – 17 ] In this c

Franz Halberg had very many experiences in India. The word circadian and chronobiology, chronocardiology and chronoastrobiology were coined by him. He also discovered that in studies of single daily meals, eating breakfast was associated with weight loss compared to dinner, despite similar energy intake. The role of time-adjusted drug intake, especially in the early morning, was also known to ancient Indian physicians. In Ayurveda, drinking of large amounts of water in the early morning is advised, which appears to be in an attempt to increase vagal tone due to gastric distention. A circadian cell cycle resides in every cell, and peripheral timing mechanisms are being documented in molecular biologic terms at about 24-hour (circadian) and higher (ultradian) frequencies, with coordination, in mammals, by the adrenal and the pineal-hypothalamic-pituitary network. The suprachiasmatic nuclei (SCN) and clock gene contribute to the coordination of the circadian rhythms' phase and amplitude, in every day life. The SCN are influenced by the daily alternation between light and darkness directly via the eyes and by plasma melatonin concentrations secreted by the pineal gland, which is a window to both light and geomagnetics. A clinical event occurs when our neuroendocrine time structures (chronomes) are not able to cope with the adverse effects of stimuli from within or from without, acting, e.g., via the sympathetic nervous system. Triggering of the neuroendocrines by environmental fa