Feeding during the rest phase promotes circadian conflict in nuclei that control energy homeostasis and sleep-wake cycle in rats

A Late Meal Timing Pattern Is Associated with Insulin Resistance in European Children and Adolescents

Meal timing has been associated with metabolic markers in adults, but not in children or adolescents. The aim of this study was to investigate associations of meal timing patterns (MTPs) with insulin resistance (IR) and triglyceride levels in children and adolescents. In this cross-sectional study, we included 2,195 participants aged 8-15 years from the European I.Family study (2013/14). Habitual diet exposures were derived using 24-hr dietary recalls and HOMA-IR, HbA1c, and triglycerides were used as metabolic outcome variables. We applied k-means cluster analysis on five dietary exposures (energy proportion in the morning and evening, eating window, pre-sleep fasting and eating frequency), which revealed the following three MTPs: "early-often", "late-long" and "late-infrequent-short". We used linear mixed models to estimate the associations between MTPs and the z-scores of the metabolic outcome variables. The association analysis revealed differences between MTPs in HOMA-IR but not in HbA1c or triglyceride z-scores. The "late-infrequent-short" pattern was associated with a 0.19 (95%-CI: (0.01, 0.36)) higher HOMA-IR z-score compared to the "early-often" pattern in the model adjusted for age, BMI z-score, education, sex, country, and family membership. These findings suggest that the timing of meals may influence IR already in childhood and adolescence. Therefore, the time of meals should be considered in future nutrition research and dietary advice for children and adolescents.

Feeding during the resting phase causes gastrointestinal tract dysfunction and desynchronization of metabolic and neuronal rhythms in rats

BACKGROUND

Disrupted circadian rhythms may result from a misalignment between the environmental cycles (due to shift work, sleep restriction, feeding at an unusual time of day) and endogenous rhythms or by physiological aging. Among the numerous adverse effects, disrupted rhythms affect the brain-gut axis, contributing to the pathogenesis of several diseases in the gastrointestinal tract, for example, abdominal pain, constipation, gastric dyspepsia, inflammatory bowel disease, irritable bowel syndrome, and others.

METHODS

This study evaluated the rat gastric emptying, gastrointestinal motility, a clock gene, gut hormones, and the neuron activity on the nucleus of tractus solitarius (NTS), area postrema (AP), and the dorsal motor nucleus of the vagus (DMV) in rats with restricted food access to the rest phase for 4 weeks.

KEY RESULTS

Our results show that food restricted to the rest light period disturbed the expression pattern of a series of transcripts, including metabolic and circadian regulation. Also, the secretion of gastrointestinal hormones, gastric emptying, intestinal motility, and NTS, AP, and DMV activity were altered.

CONCLUSIONS & INFERENCES

These data indicate the importance of the time of the day food is ingested on the regulation of energy balance and the endocrine activity of the stomach and small intestine, emphasizing the importance of food as a powerful circadian synchronizer and an essential factor for the triggering of gastrointestinal diseases and metabolic problems. These findings offer a novel clue regarding the obesity-promoting effect attributed to feeding time and open the possibility of treating this and other intestinal disorders.

Minor Changes in Daily Rhythms Induced by a Skeleton Photoperiod Are Associated with Increased Adiposity and Glucose Intolerance

Eating during the rest phase is associated with metabolic syndrome, proposed to result from a conflict between food consumption and the energy-saving state imposed by the circadian system. However, in nocturnal rodents, eating during the rest phase (day-feeding, DF) also implies food intake during light exposure. To investigate whether light exposure contributes to DF-induced metabolic impairments, animals receive food during the subjective day without light. A skeleton photoperiod (SP) is used to entrain rats to a 12:12 cycle with two short light pulses framing the subjective day. DF-induced adiposity is prevented by SP, suggesting that the conflict between light and feeding stimulates fat accumulation. However, all animals under SP conditions develop glucose intolerance regardless of their feeding schedule. Moreover, animals under SP with ad libitum or night-feeding have increased adiposity. SP animals show a delayed onset of the daily rise in body temperature and energy expenditure and shorter duration of nighttime activity, which may contribute to the metabolic disturbances. These data emphasize that metabolic homeostasis can only be achieved when all daily cycling variables are synchronized. Even small shifts in the alignment of different metabolic rhythms, such as those induced by SP, may predispose individuals to metabolic disease.

Day/night Changes in the Dorsomedial Hypothalamus Firing Responses to Ghrelin are Modulated by High-fat Diet

Dorsomedial hypothalamus (DMH) is a part of the feeding center involved in food intake and regulation of the metabolism. DMH neurons express many receptors for different metabolic cues which can modulate its network and influence animals' behaviour. One of the metabolic peptides deliveredto this structure is ghrelin, the only well-known hunger signal, produced mainly in the stomach. Diet-induced obesity is a physiological model of obesity widely used in research. Here we investigated how time-of-day and high-fat diet (HFD) affect neuronal networks and the sensitivity to the metabolic information received by the DMH. Our results indicate that even a short period of HFD (2-3 weeks) consumption can cause dysregulation of the DMH neuronal network, manifested as a disruption of the day/night pattern of basal activity and altered sensitivity to incoming information. We showed for the first time a day/night pattern of sensitivity to ghrelin in the DMH, with a higher level during the behaviorally active phase of animals. This day/night rhythm of sensitivity to ghrelin was reversed in HFD group, causing a stronger effect during the non-active phase. After prolongation of the HFD consumption to 7-8 weeks we observed an increase in the responsiveness to ghrelin, than during the short-term diet.

Insulin-like Growth Factor I Couples Metabolism with Circadian Activity through Hypo-Thalamic Orexin Neurons

Uncoupling of metabolism and circadian activity is associated with an increased risk of a wide spectrum of pathologies. Recently, insulin and the closely related insulin-like growth factor I (IGF-I) were shown to entrain feeding patterns with circadian rhythms. Both hormones act centrally to modulate peripheral glucose metabolism; however, whereas central targets of insulin actions are intensely scrutinized, those mediating the actions of IGF-I remain less defined. We recently showed that IGF-I targets orexin neurons in the lateral hypothalamus, and now we evaluated whether IGF-I modulates orexin neurons to align circadian rhythms with metabolism. Mice with disrupted IGF-IR activity in orexin neurons (Firoc mice) showed sexually dimorphic alterations in daily glucose rhythms and feeding activity patterns which preceded the appearance of metabolic disturbances. Thus, Firoc males developed hyperglycemia and glucose intolerance, while females developed obesity. Since IGF-I directly modulates orexin levels and hepatic expression of KLF genes involved in circadian and metabolic entrainment in an orexin-dependent manner, it seems that IGF-I entrains metabolism and circadian rhythms by modulating the activity of orexin neurons.

Temporal dysregulation of hypothalamic integrative and metabolic nuclei in rats fed during the rest phase

Temporal coordination of organisms according to the daytime allows a better performance of physiological processes. However, modern lifestyle habits, such as food intake during the rest phase, promote internal desynchronization and compromise homeostasis and health. The hypothalamic suprachiasmatic nucleus (SCN) synchronizes body physiology and behavior with the environmental light-dark cycle by transmitting time information to several integrative hypothalamic nuclei, such as the paraventricular nucleus (PVN), dorsomedial hypothalamic nucleus (DMH) and median preoptic area (MnPO). The SCN receives metabolic information mainly via Neuropeptide Y (NPY) inputs from the intergeniculate nucleus of the thalamus (IGL). Nowadays, there is no evidence of the response of the PVN, DMH and MnPO when the animals are subjected to internal desynchronization by restricting food access to the rest phase of the day. To explore this issue, we compared the circadian activity of the SCN, PVN, DMH and MnPO. In addition, we analyzed the daily activity of the satiety centers of the brainstem, the nucleus of the tractus solitarius (NTS) and area postrema (AP), which send metabolic information to the SCN, directly or via the thalamic intergeniculate leaflet (IGL). For that, male Wistar rats were assigned to three meal protocols: fed during the rest phase (Day Fed); fed during the active phase (Night Fed); free access to food (ad libitum). After 21 d, the daily activity patterns of these nuclei were analyzed by c-Fos immunohistochemistry, as well as NPY immunohistochemistry, in the SCN. The results show that eating during the rest period produces a phase advance in the activity of the SCN, changes the daily activity pattern in the MnPO, NTS and AP and flattens the c-Fos rhythm in the PVN and DMH. Altogether, these results validate previous observations of circadian dysregulation that occurs within the central nervous system when meals are consumed during the rest phase, a behavior that is involved in the metabolic alterations described in the literature.

Crosstalk between Melanin Concentrating Hormone and Endocrine Factors: Implications for Obesity

Melanin-concentrating hormone (MCH) is a 19aa cyclic peptide exclusively expressed in the lateral hypothalamic area, which is an area of the brain involved in a large number of physiological functions and vital processes such as nutrient sensing, food intake, sleep-wake arousal, memory formation, and reproduction. However, the role of the lateral hypothalamic area in metabolic regulation stands out as the most relevant function. MCH regulates energy balance and glucose homeostasis by controlling food intake and peripheral lipid metabolism, energy expenditure, locomotor activity and brown adipose tissue thermogenesis. However, the MCH control of energy balance is a complex mechanism that involves the interaction of several neuroendocrine systems. The aim of the present work is to describe the current knowledge of the crosstalk of MCH with different endocrine factors. We also provide our view about the possible use of melanin-concentrating hormone receptor antagonists for the treatment of metabolic complications. In light of the data provided here and based on its actions and function, we believe that the MCH system emerges as an important target for the treatment of obesity and its comorbidities.

The Circadian Clock and Obesity

The modern way of life has dramatically affected our biological rhythms. Circadian rhythms, which are generated by an endogenous circadian clock, are observed in a large number of physiological functions including metabolism. Proper peripheral clock synchronization by different signals including appropriate feeding/fasting cycles is essential to coordinate and temporally gate metabolic processes. In this chapter, we emphasize the importance of nutrient sensing by peripheral clocks and highlight the major role of peripheral and central clock communication to locally regulate metabolic processes and ensure optimal energy storage and expenditure. As a consequence, changes in eating behavior and/or bedtime, as occurs upon shift work and jet lag, have direct consequences on metabolism and participate in the increasing prevalence of obesity and associated metabolic diseases such as type 2 diabetes and non-alcoholic fatty liver disease. In this setting, time-restricted feeding has been suggested as an efficient approach to ameliorate metabolic parameters and control body weight.

Involvement of the Orexinergic System in Feeding

To know the processes involved in feeding, the dysregulation of hypothalamic neuropeptides promoting anorexigenic/orexigenic mechanisms must be investigated. Many neuropeptides are involved in this behavior and in overweight/obesity. Current pharmacological strategies for the treatment of obesity are unfortunately not very effective and, hence, new therapeutic strategies must be investigated and developed. Due to the crucial role played by orexins in feeding behavior, the aim of this review is to update the involvement of the orexinergic system in this behavior. The studies performed in experimental animal models and humans and the relationships between the orexinergic system and other substances are mentioned and discussed. Promising research lines on the orexinergic system are highlighted (signaling pathways, heterogeneity of the hypothalamic orexinergic neurons, receptor-receptor interaction, and sex differences). Each of the orexin 1 and 2 receptors plays a unique role in energy metabolism, exerting a differential function in obesity. Additional preclinical/clinical studies must be carried out to demonstrate the beneficial effects mediated by orexin receptor antagonists. Because therapies applied are in general ineffective when they are directed against a single target, the best option for successful anti-obesity treatments is the development of combination therapies as well as the development of new and more specific orexin receptor antagonists.

Time-of-day as a critical biological variable

Time-of-day is a crucial, yet often overlooked, biological variable in biomedical research. We examined the top 25 most cited papers in several domains of behavioral neuroscience to determine whether time-of-day information was reported. The majority of studies report behavioral testing conducted during the day, which does not coincide with the optimal time to perform the testing from an functional perspective of the animals being tested. The majority of animal models used in biomedical research are nocturnal rodents; thus, testing during the light phase (i.e. animals' rest period) may alter the results and introduce variability across studies. Time-of-day is rarely considered in analyses or reported in publications; the majority of publications fail to include temporal details when describing their experimental methods, and those few that report testing during the dark rarely report whether measures are in place to protect from exposure to extraneous light. We propose that failing to account for time-of-day may compromise replication of findings across behavioral studies and reduce their value when extrapolating results to diurnal humans.

The Microbiota and the Gut-Brain Axis in Controlling Food Intake and Energy Homeostasis

Obesity currently represents a major societal and health challenge worldwide. Its prevalence has reached epidemic proportions and trends continue to rise, reflecting the need for more effective preventive measures. Hypothalamic circuits that control energy homeostasis in response to food intake are interesting targets for body-weight management, for example, through interventions that reinforce the gut-to-brain nutrient signalling, whose malfunction contributes to obesity. Gut microbiota-diet interactions might interfere in nutrient sensing and signalling from the gut to the brain, where the information is processed to control energy homeostasis. This gut microbiota-brain crosstalk is mediated by metabolites, mainly short chain fatty acids, secondary bile acids or amino acids-derived metabolites and subcellular bacterial components. These activate gut-endocrine and/or neural-mediated pathways or pass to systemic circulation and then reach the brain. Feeding time and dietary composition are the main drivers of the gut microbiota structure and function. Therefore, aberrant feeding patterns or unhealthy diets might alter gut microbiota-diet interactions and modify nutrient availability and/or microbial ligands transmitting information from the gut to the brain in response to food intake, thus impairing energy homeostasis. Herein, we update the scientific evidence supporting that gut microbiota is a source of novel dietary and non-dietary biological products that may beneficially regulate gut-to-brain communication and, thus, improve metabolic health. Additionally, we evaluate how the feeding time and dietary composition modulate the gut microbiota and, thereby, the intraluminal availability of these biological products with potential effects on energy homeostasis. The review also identifies knowledge gaps and the advances required to clinically apply microbiome-based strategies to improve the gut-brain axis function and, thus, combat obesity.

Effects of Irregular Feeding on the Daily Fluctuations in mRNA Expression of the Neurosecretory Protein GL and Neurosecretory Protein GM Genes in the Mouse Hypothalamus

Circadian desynchrony induced by a long period of irregular feeding leads to metabolic diseases, such as obesity and diabetes mellitus. The recently identified neurosecretory protein GL (NPGL) and neurosecretory protein GM (NPGM) are hypothalamic small proteins that stimulate food intake and fat accumulation in several animals. To clarify the mechanisms that evoke feeding behavior and induce energy metabolism at the appropriate times in accordance with a circadian rhythm, diurnal fluctuations in Npgl and Npgm mRNA expression were investigated in mice. Quantitative RT-PCR analysis revealed that the mRNAs of these two genes were highly expressed in the mediobasal hypothalamus during the active dark phase under ad libitum feeding. In mice restricted to 3 h of feeding during the inactive light phase, the Npgl mRNA level was augmented in the moment prior to the feeding period and the midnight peak of Npgm mRNA was attenuated. Moreover, the mRNA expression levels of clock genes, feeding regulatory neuropeptides, and lipid metabolic enzymes in the central and peripheral tissues were comparable to those of central Npgl and Npgm. These data suggest that Npgl and Npgm transcription fluctuates daily and likely mediates feeding behavior and/or energy metabolism at an appropriate time according to the meal timing.

Time-restricted feeding prevents depressive-like and anxiety-like behaviors in male rats exposed to an experimental model of shift-work

Individuals who regularly shift their sleep timing, like night and/or shift-workers suffer from circadian desynchrony and are at risk of developing cardiometabolic diseases and cancer. Also, shift-work is are suggested to be a risk factor for the development of mood disorders such as the burn out syndrome, anxiety, and depression. Experimental and clinical studies provide evidence that food intake restricted to the normal activity phase is a potent synchronizer for the circadian system and can prevent the detrimental health effects associated with circadian disruption. Here, we explored whether adult male Wistar rats exposed to an experimental model of shift-work (W-AL) developed depressive and/or anxiety-like behaviors and whether this was associated with neuroinflammation in brain areas involved with mood regulation. We also tested whether time-restricted feeding (TRF) to the active phase could ameliorate circadian disruption and therefore would prevent depressive and anxiety-like behaviors as well as neuroinflammation. In male Wistar rats, W-AL induced depressive-like behavior characterized by hypoactivity and anhedonia and induced increased anxiety-like behavior in the open field test. This was associated with increased number of glial fibrillary acidic protein and IBA-1-positive cells in the prefrontal cortex and basolateral amygdala. Moreover W-AL caused morphological changes in the microglia in the CA3 area of the hippocampus indicating microglial activation. Importantly, TRF prevented behavioral changes and decreased neuroinflammation markers in the brain. Present results add up evidence about the importance that TRF in synchrony with the light-dark cycle can prevent neuroinflammation leading to healthy mood states in spite of circadian disruptive conditions.

Suprachiasmatic Nucleus-Arcuate Nucleus Axis: Interaction Between Time and Metabolism Essential for Health

In mammals, time and metabolism are tightly coupled variables; this relationship can be illustrated by numerous examples, such as the circadian variation in food intake or the circadian response to a glucose bolus. We review evidence that the interaction between the suprachiasmatic nucleus and the arcuate nucleus plays a key role in the execution of these functions. The nuclei are reciprocally connected via different projections, and this interaction provides an ideal anatomical framework to modify the temporal output of the hypothalamus to metabolic organs as a consequence of the feedback from the periphery. The suprachiasmatic nucleus-arcuate nucleus relationship is essential to integrate metabolic information into the circadian system and thus adapt circadian rhythms in core body temperature, locomotor activity, food intake, and circulating molecules such as glucose and corticosterone. With the rise in obesity-associated diseases in the world population, gaining knowledge about this relationship, and the consequences of disturbing this liaison, is essential to understand the pathogenesis of obesity.

The circadian regulation of food intake

Feeding, which is essential for all animals, is regulated by homeostatic mechanisms. In addition, food consumption is temporally coordinated by the brain over the circadian (~24 h) cycle. A network of circadian clocks set daily windows during which food consumption can occur. These daily windows mostly overlap with the active phase. Brain clocks that ensure the circadian control of food intake include a master light-entrainable clock in the suprachiasmatic nuclei of the hypothalamus and secondary clocks in hypothalamic and brainstem regions. Metabolic hormones, circulating nutrients and visceral neural inputs transmit rhythmic cues that permit (via close and reciprocal molecular interactions that link metabolic processes and circadian clockwork) brain and peripheral organs to be synchronized to feeding time. As a consequence of these complex interactions, growing evidence shows that chronodisruption and mistimed eating have deleterious effects on metabolic health. Conversely, eating, even eating an unbalanced diet, during the normal active phase reduces metabolic disturbances. Therefore, in addition to energy intake and dietary composition, appropriately timed meal patterns are critical to prevent circadian desynchronization and limit metabolic risks. This Review provides insight into the dual modulation of food intake by homeostatic and circadian processes, describes the mechanisms regulating feeding time and highlights the beneficial effects of correctly timed eating, as opposed to the negative metabolic consequences of mistimed eating.

Time-Restricted Eating to Prevent and Manage Chronic Metabolic Diseases

Molecular clocks are present in almost every cell to anticipate daily recurring and predictable changes, such as rhythmic nutrient availability, and to adapt cellular functions accordingly. At the same time, nutrient-sensing pathways can respond to acute nutrient imbalance and modulate and orient metabolism so cells can adapt optimally to a declining or increasing availability of nutrients. Organismal circadian rhythms are coordinated by behavioral rhythms such as activity-rest and feeding-fasting cycles to temporally orchestrate a sequence of physiological processes to optimize metabolism. Basic research in circadian rhythms has largely focused on the functioning of the self-sustaining molecular circadian oscillator, while research in nutrition science has yielded insights into physiological responses to caloric deprivation or to specific macronutrients. Integration of these two fields into actionable new concepts in the timing of food intake has led to the emerging practice of time-restricted eating. In this paradigm, daily caloric intake is restricted to a consistent window of 8-12 h. This paradigm has pervasive benefits on multiple organ systems.

Differential Recovery Speed of Activity and Metabolic Rhythms in Rats After an Experimental Protocol of Shift-Work

The circadian system drives the temporal organization of body physiology in relation to the changing daily environment. Shift-work (SW) disrupts this temporal order and is associated with the loss of homeostasis and metabolic syndrome. In a rodent model of SW based on forced activity in the rest phase for 4 weeks, we describe the occurrence of circadian desynchrony, as well as metabolic and liver dysfunction. To provide better evidence for the impact of altered timing of activity, this study explored how long it takes to recover metabolic rhythms and behavior. Rats were submitted to experimental SW for 4 weeks and then were left to recover for one week. Daily locomotor activity, food intake patterns, serum glucose and triglycerides, and the expression levels of hepatic Pparα, Srebp-1c, Pepck, Bmal1 and Per2 were assessed during the recovery period and were compared with expected data according to a control condition. SW triggered the circadian desynchronization of all of the analyzed parameters. A difference in the time required for realignment was observed among parameters. Locomotor activity achieved the expected phase on day 2, whereas the nocturnal feeding pattern was restored on the sixth recovery day. Daily rhythms of plasma glucose and triglycerides and of Pparα, Pepck and Bmal1 expression in the liver resynchronized on the seventh day, whereas Srebp-1c and Per2 persisted arrhythmic for the entire recovery week. SW does not equally affect behavior and metabolic rhythms, leading to internal desynchrony during the recovery phase.

Circadian regulation of membrane physiology in neural oscillators throughout the brain

Twenty-four-hour rhythmicity in physiology and behavior are driven by changes in neurophysiological activity that vary across the light-dark and rest-activity cycle. Although this neural code is most prominent in neurons of the primary circadian pacemaker in the suprachiasmatic nucleus (SCN) of the hypothalamus, there are many other regions in the brain where region-specific function and behavioral rhythmicity may be encoded by changes in electrical properties of those neurons. In this review, we explore the existing evidence for molecular clocks and/or neurophysiological rhythms (i.e., 24 hr) in brain regions outside the SCN. In addition, we highlight the brain regions that are ripe for future investigation into the critical role of circadian rhythmicity for local oscillators. For example, the cerebellum expresses rhythmicity in over 2,000 gene transcripts, and yet we know very little about how circadian regulation drives 24-hr changes in the neural coding responsible for motor coordination. Finally, we conclude with a discussion of how our understanding of circadian regulation of electrical properties may yield insight into disease mechanisms which may lead to novel chronotherapeutic strategies in the future.

Time-Lag in Feeding Schedule Acts as a Stressor That Alters Circadian Oscillators in Goldfish

The circadian system controls temporal homeostasis in all vertebrates. The light-dark (LD) cycle is the most important zeitgeber (“time giver”) of circadian system, but feeding time also acts as a potent synchronizer in the functional organization of the teleost circadian system. In mammals is well known that food intake during the rest phase promotes circadian desynchrony which has been associated with metabolic diseases. However, the impact of a misalignment of LD and feeding cycles in the entrainment of fish circadian oscillators is largely unknown. The objective of this work was to investigate how a time-lag feeding alters temporal homeostasis and if this could be considered a stressor. To this aim, goldfish maintained under a 12 h light-12 h darkness were fed at mid-photophase (SF6) or mid-scotophase (SF18). Daily rhythms of locomotor activity, clock genes expression in hypothalamus, liver, and head kidney, and circulating cortisol were studied. Results showed that SF6 fish showed daily rhythms of bmal1a and clock1a in all studied tissues, being in antiphase with rhythms of per1 genes, as expected for proper functioning clocks. The 12 h shift in scheduled feeding induced a short phase advance (4–5-h) of the clock genes daily rhythms in the hypothalamus, while in the liver the shift for clock genes expression rhythms was the same that the feeding time shift (∼12 h). In head kidney, acrophases of per genes underwent a 12-h shift in SF18 animals, but only 6 h shift for clock1a. Plasma cortisol levels showed a significant daily rhythm in animals fed at SF6, but not in SF18 fish fed, which displayed higher cortisol values throughout the 24-h. Altogether, results indicate that hypothalamus, liver, and head kidney oscillate in phase in SF6 fish, but these clocks are desynchronized in SF18 fish, which could explain cortisol alterations. These data reinforce the hypothesis that the misalignment of external cues (daily photocycle and feeding time) alters fish temporal homeostasis and it might be considered a stressor for the animals.

Shift-work: is time of eating determining metabolic health? Evidence from animal models

The circadian disruption in shift-workers is suggested to be a risk factor to develop overweight and metabolic dysfunction. The conflicting time signals given by shifted activity, shifted food intake and exposure to light at night occurring in the shift-worker are proposed to be the cause for the loss of internal synchrony and the consequent adverse effects on body weight and metabolism. Because food elicited signals have proven to be potent entraining signals for peripheral oscillations, here we review the findings from experimental models of shift-work and verify whether they provide evidence about the causal association between shifted feeding schedules, circadian disruption and altered metabolism. We found mainly four experimental models that mimic the conditions of shift-work: protocols of forced sleep deprivation, of forced activity during the normal rest phase, exposure to light at night and shifted food timing. A big variability in the intensity and duration of the protocols was observed, which led to a diversity of effects. A common result was the disruption of temporal patterns of activity; however, not all studies explored the temporal patterns of food intake. According to studies that evaluate time of food intake as an experimental model of shift-work and studies that evaluate shifted food consumption, time of food intake may be a determining factor for the loss of balance at the circadian and metabolic level.