Are you a morning lark or a night owl?

Whether you’re a “morning person” or a “night person” may have something to do with your gut bacteria. A collaborative research project between the University of Haifa and the Technion has found that “morning people” and “night people” differ from each other in their gut microbiome – the bacterial populations that inhabit our digestive tract.

The study was conducted in collaboration between researchers and a number of research groups at the two universities: Assistant Professor Naama Geva-Zatorsky, head of the Microbiome Research Lab of the Rappaport Faculty of Medicine at the Technion, and her Ph.D. student Shaqed Carasso; Associate Professor Eran Tauber, head of the Biological Clock Lab in the Department of Evolutionary and Environmental Biology at the University of Haifa, and his lab manager Dr Bettina Fishman; and Professor Tamar Shochat and research student Liel Stelmach Lask, of the Cheryl Spencer Department of Nursing at the University of Haifa. The challenge was to examine differences in gut microbiome composition between early risers and night people.

“This is the first time that a connection has been found between people’s gut microbiome, eating behavior and sleep patterns,” said Prof. Tauber. “These discoveries are likely to pave the way to change these patterns by altering one’s diet.”

Every person falls into one of three chronotypes: “larks,” who are morning people who get up early and are at their best in the morning; “owls,” who are night people who go to bed late and have a hard time functioning in the morning; and the intermediate group, which is made up of most of the population. Studies conducted in recent years found significant differences between the different chronotypes – physiological, cognitive, and in the structure of their personality.

Initial evidence from Prof. Tauber’s lab suggests that changes in gut microbiome composition may affect chronotype identity, prompting the collaboration between the Technion and the University of Haifa. The researchers recruited volunteers from across Israel, who sent in stool samples and reported on their sleep patterns and eating behaviors. The researchers characterized the composition of the gut flora of 91 volunteers belonging to the three chronotypes (morning people, night people, and intermediate types) through DNA sequencing of the samples.

Among “larks,” the researchers found a higher percentage of the bacterial genus Alistipes, whereas among “owls,” the bacteria belonging to the Lachnospira genus were higher. Lachnospira bacteria produce butyrate, a short-chain fatty acid that is a source of signals related to sleep and wakefulness.

When the researchers reviewed the daily diets of the subjects through questionnaires, they found additional significant differences between morning larks and night owls: morning people eat far more fruits and vegetables, drink mainly water, and do not eat complex carbohydrate. Night people, though, were found to eat a high-fat diet with a lot of meat and fewer fruits, and drink beverages containing large amounts of sugar.

“Studies at our lab and other labs active in this sphere, show that our gut microbiome composition and our health are closely connected,” said Prof. Geva-Zatorsky. “Moreover, our eating behaviors, diet, and habits can affect our gut microbiome composition. The present research focuses on healthy people and paves the way to characterizing not only how bacteria vary between different chronotypes, but also to an understanding of how gut bacteria are affected by our habits and how they might affect us. It is important to note that causality was not yet proven, and this shall be the focus of our next study.”

Indeed, according to the researchers, it is still too early to determine whether the difference in microbiome composition influences the attribution to the different chronotypes or is influenced by it, or if the causality at play here is more complex. That said, the fact that for the first time a connection of this kind has been found opens up opportunities for an examination of the subject.

“The customary daily routine in Western society today often makes things tough for night owls,” said Prof. Tauber. “They go to bed late and have to get up relatively early to go about their daily duties, so they often suffer from a lack of sleep. We also know that many night people suffer from problems like depression, diabetes and obesity. We hope that if we can change the bacterial populations that inhabit our digestive tract, for example, by making changes in our diet and eating habits, we might be able to influence the sleep patterns of owls and improve their quality of life.”

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Naama Geva-Zatorsky
Naama Geva-Zatorsky