Background There is emerging literature demonstrating a relationship between the timing of feeding and weight regulation in animals. However, whether the timing of food intake influences the success of a weight-loss diet in humans is unknown. Objective To evaluate the role of food-timing in weight-loss effectiveness in a sample of 420 individuals who followed a 20-week weight-loss treatment. Methods Participants (49.5% females; age [mean+/−SD]: 42±11 years; BMI: 31.4±5.4 kg/m2) were grouped in early-eaters and late-eaters, according to the timing of the main meal (lunch in this Mediterranean population). 51% of the subjects were early-eaters and 49% were late-eaters (lunch time before and after 3:00 PM, respectively), energy intake and expenditure, appetite hormones, CLOCK genotype, sleep duration and chronotype were studied. Results Late lunch eaters lost less weight and displayed a slower weight-loss rate during the 20 weeks of treatment than early-eaters (P=0.002). Surprisingly, energy intake, dietary composition, estimated energy expenditure, appetite hormones and sleep duration was similar between both groups. Nevertheless, late-eaters were more evening-types, had less energetic breakfasts, and skipped breakfast more frequently that early-eaters (P<0.05). CLOCK rs4580704 SNP associated with the timing of the main meal (P=0.015) with a higher frequency of minor allele (C) carriers among the late-eaters (P=0.041). Neither sleep duration, nor CLOCK SNPs or Morning/Evening chronotype was independently associated with weight-loss (P>0.05). Conclusions Eating late may influence the success of weight-loss therapy. Novel therapeutic strategies should incorporate not only the caloric intake and macronutrient distribution—as is classically done—but also the timing of food.

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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.

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Acute melatonin administration in humans impairs glucose tolerance in both the morning and evening. When administering melatonin, the proximity to meal timing may need to be considered, particularly in those at risk for glucose intolerance.