Eating late is associated with decreased resting-energy expenditure, decreased fasting carbohydrate oxidation, decreased glucose tolerance, blunted daily profile in free cortisol concentrations and decreased thermal effect of food on Twrist. These results may be implicated in the differential effects of meal timing on metabolic health.

The composition of the diet (what we eat) has been widely related to the microbiota profile. However, whether the timing of food consumption (when we eat) influences microbiota in humans is unknown. A randomized, crossover study was performed in 10 healthy normal-weight young women to test the effect of the timing of food intake on the human microbiota in the saliva and fecal samples. More specifically, to determine whether eating late alters daily rhythms of human salivary microbiota, we interrogated salivary microbiota in samples obtained at 4 specific time points over 24 h, to achieve a better understanding of the relationship between food timing and metabolic alterations in humans. Results revealed significant diurnal rhythms in salivary diversity and bacterial relative abundance (i.e., TM7 and Fusobacteria) across both early and late eating conditions. More importantly, meal timing affected diurnal rhythms in diversity of salivary microbiota toward an inverted rhythm between the eating conditions, and eating late increased the number of putative proinflammatory taxa, showing a diurnal rhythm in the saliva. In a randomized, crossover study, we showed for the first time the impact of the timing of food intake on human salivary microbiota. Eating the main meal late inverts the daily rhythm of salivary microbiota diversity which may have a deleterious effect on the metabolism of the host.-Collado, M. C., Engen, P. A., Bandín, C., Cabrera-Rubio, R., Voigt, R. M., Green, S. J., Naqib, A., Keshavarzian, A., Scheer, F. A. J. L., Garaulet, M. Timing of food intake impacts daily rhythms of human salivary microbiota: a randomized, crossover study. FASEB J. 32, 2060FASEB J. 32, -2072FASEB J. 32, (2018. www.fasebj.orgRecent studies suggest that not only what we eat, but also when we eat may have a significant role in obesity treatment and metabolic alterations (1-6). Unusual feeding times can induce a disruption of the circadian system, which may lead to metabolic dysfunction (7-11). For example, in a longitudinal study of an overweight and obese Mediterranean population, our group demonstrated that those who ate lunch later in the day (main meal for this population) lost significantly less weight than those who ate lunch early, although early eaters (EEs) and late eaters (LEs) showed similar food intake, physical activity, sleep duration, and appetite-related hormone levels (2). Moreover, LEs had significantly higher insulin resistance. In the same line, a randomized, crossover study demonstrated that meal timing affects glucose tolerance, suggesting that eating late increases metabolic risk, even in healthy women (7).The importance of caloric distribution across the day in weight loss effectiveness was supported by a 12-wk experimental study showing that participants assigned to high caloric intake during breakfast lost significantly more weight than those assigned to high caloric intake ABBREVIATIONS: ANOSIM, analysis of similarity; BMI, body mass index; EE, early eater; F/B, Firmicutes/Bacteroidetes; FD...

https://clinicaltrials.gov/ct2/show/NCT03003936.

Circadian rhythms at the beginning of the treatment are good predictors of future weight loss. Further treatment should consider chronobiological aspects to diagnose obesity and effectiveness of treatments.