Order and disorder: temporal organization of eating

Complex physiology and clinical implications of time-restricted eating

Time-restricted eating (TRE) is a dietary intervention that limits food consumption to a specific time window each day. The effect of TRE on body weight and physiological functions has been extensively studied in rodent models, which have shown considerable therapeutic effects of TRE and important interactions among time of eating, circadian biology, and metabolic homeostasis. In contrast, it is difficult to make firm conclusions regarding the effect of TRE in people because of the heterogeneity in results, TRE regimens, and study populations. In this review, we 1) provide a background of the history of meal consumption in people and the normal physiology of eating and fasting; 2) discuss the interaction between circadian molecular metabolism and TRE; 3) integrate the results of preclinical and clinical studies that evaluated the effects of TRE on body weight and physiological functions; 4) summarize other time-related dietary interventions that have been studied in people; and 4) identify current gaps in knowledge and provide a framework for future research directions.

Temporal relationships between food acquisition and voluntary exercise in mice

Patterns of operant food acquisition in a closed economy and bouts of either voluntary wheel running (WR) or spontaneous locomotor activity in a standard condition (SC) with no wheel were examined in young adult male and female C57BL/6 mice across a range of nose poke prices (FUP) per food pellet. Both sexes showed vigorous WR or locomotor activity. At each FUP, WR groups had higher food intake than SC groups. Despite substantially higher mean body weight of males compared with females, intakes and activity did not differ by sex in the SC groups and males lost weight more rapidly as FUP increased. In contrast, WR males ran ∼33% further per day than females, increased their food intake (above that of SC counterparts) more than females, and lost less body weight than SC males. By parsing the night in four 3h epochs it was found that food intake declined progressively through the night in both WR and SC mice and that the hyperphagia of WR relative to SC groups was most evident early in the night, coincident with highest activity. No large or systematic sex differences were revealed in these temporal analyses. Analysis of data at 60s resolution showed that pellet acquisition occurred in many small or short bouts, the timing of which was either intercalated or concurrent with either locomotor activity or WR. The results show that increased eating due to WR occurs concurrently with maximum running, and with no evidence of delayed compensation.

Restricted temporal access to food and anorexia in mice: Microstructure of eating within feeding opportunities

Intake and body weight were recorded in a closed economy as male and female C57BL/6 mice progressed through either fixed interval (FI) or fixed unit price (FUP) schedules of cost for 20-mg food pellets. Access to food was constrained to four 40 min food opportunities (FOs) per day, spaced 4-h apart through the dark phase. Nose poke responses and pellet deliveries were collected at 10-s resolution to allow pellet-by-pellet analysis. In the FI protocol, mice maintained adequate food intake and body weight through the study, even though at the highest FI (50-s) they spent the entire 40-min FOs engaged in eating at or near the maximum rate allowed by the schedule. In the FUP protocol, mice greatly reduced their intake and lost weight at the highest FUP (50 responses/pellet). The analysis of response and pellet distributions showed these mice were not filling the FOs with responding and ate less at dusk (FO #1) and dawn (FO #4) than at FOs #2 and 3 in the middle of the night. The principal, and unexpected, sex difference was that females tended to eat more than males despite lower body weight, but behavioral changes as a function of feeding cost or schedule were qualitatively similar in both sexes. These results show that slow eating as imposed by an FI is not sufficient to produce hypophagia and, in the FUP protocol, hypophagia cannot be explained by slowed eating due to response requirements. We discuss the role of effort or time in FUP-induced anorexia, and suggest this murine model may emulate some aspects of human anorexia nervosa better than current activity-based protocols.

Human diet and cognition

Cognition influences what, when and how much we eat, which in turn affects the brain and hence cognition. In this overview, focusing mainly on the human literature, we start by examining cognitive influences on food and eating. This includes food preferences and choices (e.g., effects of learning, advertising, and cultural taboos), food habits relating to when and how much to eat (e.g., the concept of meals, dieting, and hunger strikes), the perception of food (e.g., the influence of appearance, food labels, and conceptions of naturalness), and how food perception is influenced by expertise. We also review how these various influences are disrupted by abnormalities of cognition (e.g., Gourmand syndrome, amnesia, and anorexia nervosa). The second part of the overview focuses on how diet affects cognition. We start by looking at the acute effects of diet, notably the impact of breakfast on cognitive performance in children. This is followed by a review of the effects of extended dietary exposures-years and lifetimes of particular diets. Here we look at the impacts of protein-energy malnourishment and Western-style diets, and their different, but adverse affects on cognition, and the beneficial effects on cognition of breast-feeding and certain dietary practices. We then outline how diet and cooking may have allowed the evolution of the large energy-hungry human brain. This overview serves to illustrate the multiple interactions that exist between cognition and diet, their importance to health and disease, and their impact on thinking about the role of conscious processes in decision making. WIREs Cogn Sci 2014, 5:463-475. doi: 10.1002/wcs.1290 For further resources related to this article, please visit the WIREs website.

CONFLICT OF INTEREST

The authors have declared no conflicts of interest for this article.

Differences in temporal aspects of food acquisition between rats and two strains of mice in a closed operant economy

Rats and mice were studied for changes in meal-taking structure in a closed operant food economy, in which the consummatory or unit prices for food were increased. In experiment 1, as food price increased, male rats modestly decreased the number of meals per day and increased mean meal size. Female rats were similar to males but had smaller meal size and, at low costs, took more meals per day. In experiment 2, male and female B6 mice reduced food intake as price increased, accompanied by decreased meal number without change in meal size. They showed grazing-like behavior in the first part of the night. In contrast, we report in experiment 3, a large increase in intake and meal size during the final trimester of pregnancy. In experiment 4, we report that CD1 male mice subjected to a unit price series performed comparably to rats, and not like B6 mice. Other CD1 mice were tested using an interval schedule, and we found that mice were able to adapt eating patterns to greatly increased time demands without compromising total intake. Data are discussed in terms of the intercalation of food acquisition with global patterns of activity. Such interactions of organism and food environment are in particular need of mechanistic investigation.

The behavioral pharmacology of anorexigenic drugs in nonhuman primates: 30 years of progress

Comparatively few studies over the past 30 years have used pharmacological manipulations as a means of understanding processes underlying feeding behavior of nonhuman primates. In the 1970s and early 1980s, four laboratories provided data on the anorexigenic effects of a range of drugs on rhesus monkeys and baboons, and a fifth laboratory studied the effects of neuropeptides on feeding behavior of baboons. There were differences in the way anorexigenic drugs altered eating topography, and those that increased dopamine levels had greater abuse liability than those that increased serotonin levels. Studies in the 1980s and 1990s used foraging models and principles of behavioral economics to understand food-drug interactions. Experimenter-given anorexigenic drugs did not function as economic substitutes for food. Recent studies have examined the effects of a range of drugs on consumption of highly palatable food and model diet-induced obesity. Although some drugs, including stimulants, N-methyl-D-aspartate antagonists, and a cannabinoid antagonist increased the latency to standard food consumption, there was little evidence for a selective effect of any drug on highly palatable food consumption. Results obtained in nonhuman primates did not always confirm those observed in rodents. Future studies looking at sex differences and social factors may provide insight into factors related to human obesity.