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Social jet lag: Sleeping in on the weekends impacts your gut health

Our internal clocks, often dictated by societal norms and work schedules, could be affecting our health in subtle yet impactful ways. 

A recent study from The European Journal of Nutrition has uncovered a potential link between irregular sleeping patterns and the presence of harmful gut bacteria.

Gut microbiome 

The gut microbiome, an extensive community of bacteria, viruses, fungi, and other microorganisms residing in our intestines, plays a pivotal role in our health. 

While some of these microorganisms contribute positively, assisting in digestion and secreting beneficial metabolites, others can be detrimental, releasing harmful toxins. 

The composition of the gut microbiome can be significantly influenced by our diet, thereby altering the diversity of microbial species present and our susceptibility to various health conditions.

By choosing what we eat, we can influence which types of microorganisms flourish and, in turn, potentially reduce our risk of various long-term health conditions.

Social jet lag

In the past, studies have shown that major disruptions to the body’s internal clock, like those experienced by shift workers, can elevate the risk of weight gain, heart issues, and diabetes. 

However, there’s a lesser-understood relationship: how minor shifts in our sleep schedule, caused by societal obligations, might affect our health. 

This phenomenon, known as “social jet lag,” refers to the difference in sleep patterns between workdays and non-workdays. Prior research has linked social jet lag to issues such as weight gain and mental fatigue.

Focus of the study

Delving deeper into this, researchers from the ZOE PREDICT nutritional study analyzed blood, stool samples, and glucose measurements. 

By comparing data from participants with irregular sleep patterns to those with more routine sleep schedules, the team aimed to discern if the microbiome was affected by social jet lag. 

Notably, the participants were primarily lean and healthy, distinguishing this research from previous studies that often focused on individuals with obesity or diabetes.

What the researchers discovered 

The study’s findings, based on data from 934 participants, were very clear. Even a 90-minute variance in the “midpoint” of sleep (the midpoint between when a person falls asleep and wakes up) resulted in noticeable changes in the gut microbiome’s composition.

Other lifestyle habits were identified as potential contributors to social jet lag, including a low-quality diet, high intake of sugar-sweetened beverages, and reduced consumption of fruits and nuts – all of which can directly modify the gut microbiome.

Among the gut microorganisms linked with social jet lag, three species were identified as having “unfavorable” health effects. These particular microorganisms are also associated with poor diet quality, obesity indicators, and inflammation markers, suggesting increased cardiovascular disease risk.

Implications of the study

Dr. Wendy Hall, the study’s senior author from King’s College London, noted: “This is the first study to show that even small differences in sleep timings across the week seem to be linked to differences in gut bacterial species.” 

“Some of these associations were linked to dietary differences, but our data also indicates that other, as yet unknown, factors may be involved.” 

Dr. Hall emphasized the need for intervention trials to understand if regularizing sleep can induce positive changes in the gut microbiome.

Dr. Sarah Berry, chief scientist at ZOE, reinforced the significance of maintaining regular sleep patterns for overall health. She emphasized that such a simple lifestyle modification can positively impact our health through our gut microbiome.

More about social jet lag

Social jet lag refers to the misalignment between our body’s internal clock (or circadian rhythm) and our social schedules, which often differ from our natural sleep patterns. This is commonly seen when people have a different sleep schedule on weekends compared to weekdays.

For example, someone might go to bed late and wake up late on weekends but need to wake up early for work or school during the week. This discrepancy can lead to a feeling similar to jet lag experienced after traveling across time zones.

Social jet lag can have negative effects on one’s health, mood, and cognitive functions, as it can disrupt the natural circadian rhythm. Some studies suggest it may be linked to obesity, mental health issues, and other chronic conditions. Reducing social jet lag involves trying to keep a consistent sleep schedule throughout the week.


The ZOE PREDICT study is the world’s largest in-depth nutritional research program, led by scientists from institutions such as King’s College London, Stamford University, Massachusetts General Hospital and Harvard University.

Primary goals of the study

Personalized nutrition responses

One of the main objectives of the ZOE PREDICT study is to understand how and why different individuals have unique metabolic responses to the same foods. This is to tackle the one-size-fits-all approach to nutrition and explore a more personalized strategy for health and well-being.

Large-scale data collection

Thousands of participants are involved, with the study collecting a plethora of data, including blood glucose levels, fat levels in the bloodstream, insulin resistance, and other key metrics following meals. The aim is to comprehensively understand food’s impact on the body.

Gut microbiome analysis

Recognizing the crucial role the gut microbiome plays in health, digestion, and potentially even mood, the study also analyzes participants’ gut bacteria. This aspect of the study contributes valuable information on how gut health influences individual food responses.

In-depth participant profiling

Before the food response tests, participants are profiled for various factors, including their current diet, health status, physical activity levels, sleep patterns, and more.

Real-world application

Beyond the academic and scientific implications, the findings from the ZOE PREDICT study have practical applications. 

For instance, the knowledge gleaned can potentially be used to develop personalized diet plans tailored to an individual’s unique biology, thereby optimizing health and potentially mitigating disease risk.


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