The purpose of this investigation is to test the hypothesis that in humans, eating late may induce changes in saliva microbiota daily rhythms towards a more obesogenic and a less responsiveness to dietary treatments profile. These changes in microbiota may partly explain the weight loss difficulties that characterized late eaters in previous studies. Thus, the aim is to analyze the effect of the timing of food intake in humans' saliva microbiome daily rhythms in a randomized, crossover interventional study, in order to achieve.

Overweight and obesity can currently be considered a major threat to human health. Recent studies suggest that not only "what" we eat, but also "when" we eat may have a significant role in obesity treatment. The importance of caloric distribution across the day on weight loss therapy was supported by a 12-weeks experimental study showing that subjects assigned to high caloric intake during breakfast lost significantly more weight than those assigned to high caloric intake during the dinner. These results suggest that eating late may affect obesity and impair the success of weight loss therapies.

Novel evidence from animal and human studies indicates that the composition of the gut microbiota may also be involved in obesity and weight loss. Moreover, studies performed in extreme obese subjects have demonstrated that weight loss improves the obesity-associated gut microbiota composition towards a lean microbiome phenotype.

A recent study has shown that the timing of food intake influences microbiota in mice model. This study reported that obesity dampens the cyclical changes in the gut microbiome of mice while time-restricted feeding (TRF), in which feeding is consolidated to the nocturnal phase, partially restores these cyclical fluctuations. Furthermore, TRF which protects against obesity and metabolic diseases affects bacteria and has shown to influence host metabolism. Then, feeding pattern and time of food intake, in addition to diet, are important parameters when assessing the microbiome's contribution to mice metabolism. However, to our knowledge no human studies are available showing the effect of timing of food intake in microbiota.

Thus, the aim was to analyze the effect of the timing of food intake in humans' saliva microbiome, in order to achieve a better understanding of the relationship between food timing, obesity and weight loss in humans.

This goal will be achieved through a specific approach:

• Interventional (randomized, cross-over controlled trials) (Aim 1): To study that, eating late may induce changes in saliva microbiota daily rhythms towards a more obesogenic pattern and a less responsiveness to dietary treatments profile in women (n=10).

Inclusion Criteria:

• Healthy women
• Body Mass Index: 20 to 30 kg/m2
• Caucasian
• Day workers

Exclusion Criteria:

• Endocrine (Diabetes mellitus or others), renal, hepatic, cancer or psychiatric disorders
• Receiving any pharmacologic treatment other than oral contraceptives
• Bulimia diagnosis, prone to binge eating
• Pregnancy

Spain: Ministry of Health and consumption