Eating when the Spanish do, is bad for the health!

Eating lunch too late modifies the composition of the intestinal and salivary microbiotas, and can contribute to the development of various problems such as obesity and some inflammatory bowel diseases (IBD), according to the results of an international team.


Diet can exert a considerable influence on the composition of our microbiota and play a role in the development of obesity and metabolic diseases. For the first time, researchers have studied the potential impact of the time we eat our meals, and in particular lunch.

Eating early or late

Spanish researchers proposed to ten young women of normal weight (body mass index between 20 and 24) that they take part in a study aiming to measure the effect of meal times on the salivary and fecal microbiotas. The participants were divided into two groups: for a week, they all took their breakfast and dinner at the same time (8.30 a.m. and 9 p.m. respectively). Only the time they ate lunch differed: 2.30 p.m. for the “early” group, 5.30 p.m. for the “late” group–it is Spain after all! The following week, they all reverted to their usual schedule for seven days, after which they changed group for the final week of monitoring. Samples of saliva were taken on waking, then every four hours up until midnight, throughout the whole study; a fecal sample was taken at the end of each week.

A modified salivary flora

One week of late lunches was enough to modify the composition of the salivary microbiota, with respect to both the diversity and abundance of its microorganisms. The researchers discovered the existence of daily fluctuations in the diversity of the salivary microbes, which were significantly affected by the time that lunch was eaten. The later this meal was taken, the greater the bacterial diversity. And it is known that the more bacterial species are present in the salivary microbiota, the greater the risk of obesity and periodontal disease. Eating lunch too late could therefore increase these risks.

What of the fecal microbiota?

The fecal microbiota was impacted to a lesser extent: in women who ate lunch late, it was richer in bacterial species that are associated with an increased risk of inflammatory gastrointestinal diseases, colorectal cancer, and insulin resistance. The time at which meals are taken therefore seems to contribute to the development of various metabolic disorders, and could, for this reason, represent a preventive tool that should not be disregarded.



Maria Carmen Collado et al.Timing of food intake impacts daily rhythms of human salivary microbiota: a randomized, crossover study. The Faseb Journal, Vol. 32 No. 4, pp. 2060-2072