Delaying mealtimes reduces fat oxidation: A randomized, crossover, controlled feeding study.

OBJECTIVE: This study investigated the effects of circadian misalignment (CM), induced by delaying mealtimes, independent of sleep timing and duration and eating window duration, on energy expenditure (EE), respiratory quotient (RQ), and substrate oxidation. METHODS: Healthy adults, aged 20 to 49 years, participated in this randomized crossover study under controlled feeding conditions. Eating window duration was identical in both conditions (circadian alignment [CA]: 9:00 am-7:00 pm; CM: 1:00 pm-11:00 pm), and bedtimes were constant (11:30 pm-8:00 am). EE, RQ, and substrate oxidation were obtained over 23 hours in a metabolic chamber on days 3 and 4 and days 14 and 15 in each condition. Twenty-four-hour and post-meal outcomes were analyzed using a linear mixed-effects model including condition, day, and day-by-condition interaction as main predictors and sex as a covariate. RESULTS: Three men and four women (age 37.4 ± 8.8 years, BMI 30.4 ± 3.3 kg/m2 ) completed the study. Twenty-four-hour EE did not differ between conditions. Post-meal RQ for dinner and snack was higher in CM versus CA (both p < 0.001) with correspondingly higher glucose oxidation (both p < 0.01) and lower fat oxidation (dinner only p = 0.0001). CONCLUSIONS: CM, induced by delaying mealtimes by 4 hours relative to CA, independently shifts nutrient metabolism toward greater carbohydrate and lower fat oxidation.

Evening Chronotype Is Associated with Poorer Habitual Diet in US Women, with Dietary Energy Density Mediating a Relation of Chronotype with Cardiovascular Health.

BACKGROUND: An innate preference for later timing of sleep and activity, termed evening chronotype, is linked to poorer cardiovascular health (CVH). However, associations of chronotype with specific health behaviors in US women are not well characterized. Of particular interest is habitual diet, because <1% of US adults meet recommendations for a healthful diet. OBJECTIVES: We aimed to evaluate cross-sectional and prospective associations of chronotype with diet quantity and quality in US women, and to assess whether dietary energy density (ED), a robust predictor of cardiometabolic outcomes, mediates an established chronotype-CVH relation. METHODS: Data were collected from participants in the AHA Go Red for Women Strategically Focused Research Network cohort (aged 20-76 y; 61% racial/ethnic minority) at baseline (n = 487) and 1-y follow-up (n = 432). Chronotype (evening compared with morning/intermediate) and habitual diet were ascertained from the Morningness-Eveningness Questionnaire and an FFQ, respectively. Multivariable-adjusted linear regression models evaluated cross-sectional and prospective associations of chronotype with diet. Causal mediation analyses assessed whether dietary ED mediated a relation between chronotype and CVH, quantified using AHA Life's Simple 7 score, derived from clinical measurements and validated assessments of CVH components. RESULTS: Evening compared with morning/intermediate chronotype was associated with poorer diet quality, including lower intakes of plant protein (cross-sectional: ß = -0.63 ± 0.24, P < 0.01; prospective: ß = -0.62 ± 0.26, P = 0.01), fiber (cross-sectional: ß = -2.19 ± 0.65, P < 0.001; prospective: ß = -2.39 ± 0.66, P < 0.001), and fruits and vegetables (cross-sectional: ß = -1.24 ± 0.33, P < 0.001; prospective: ß = -1.15 ± 0.36, P = 0.001). Evening chronotype was also associated with higher dietary ED at baseline (ß = 0.20 ± 0.05, P = 0.001) and 1 y (ß = 0.19 ± 0.06, P = 0.001). Dietary ED was a partial mediator of the association between evening chronotype and poorer CVH (24.6 ± 9.1%, P < 0.01). CONCLUSIONS: Evening chronotype could contribute to unhealthful dietary patterns in US women, with higher dietary ED partially mediating the relation between eveningness and poorer CVH. Behavioral interventions to reduce dietary ED might mitigate cardiovascular disease risk in women with evening chronotype.

Does sex influence the effects of experimental sleep curtailment and circadian misalignment on regulation of appetite?

Sleep curtailment and circadian misalignment disrupt energy sensing and eating behaviors, which can contribute to weight gain and obesity-related comorbidities. Herein, we review the effects of experimental manipulations of sleep duration and circadian alignment on circulating concentrations of appetite hormones, specifically leptin and ghrelin. Further, we focus on sex differences in hormonal and behavioral responses related to food intake. The studies reviewed suggest potential sex-specific effects of sleep curtailment on key hormones involved in the gut-brain axis, presumably leading to downstream effects on neural processes involved in food seeking and consumption behaviors. However, there is insufficient evidence to declare any sex-specific effects of circadian misalignment on appetite regulation. More research is needed to elucidate the complex sex-specific relationships between sleep, circadian rhythms, energy homeostasis, and appetite regulating mechanisms. Greater knowledge of these mechanisms would aid in the development of targeted methods to mitigate risk for obesity and related metabolic diseases.

Circadian rhythms and meal timing: impact on energy balance and body weight.

Energy metabolism and appetite regulating hormones follow circadian rhythms which, when disrupted, could lead to adverse metabolic consequences. Such circadian misalignment, a mismatch between endogenous circadian rhythms and behavior, is most severely experienced by shift workers, due to nighttime wake, daytime sleep, and eating at night. However, circadian misalignment is not restricted to shift workers; milder shifts in sleep and mealtimes, termed social and eating jetlag, are highly prevalent in the general population. Social and eating jetlag result in later mealtimes, which may promote positive energy balance and weight gain. Earlier meal timing, specific to individual endogenous circadian patterns, could serve to reduce cardiometabolic disease burden and aid in weight loss and interventions should be done to test this.