The peer-reviewed study, published in the European Journal of Nutrition on Wednesday, saw scientists from the U.K., Sweden, the U.S., and Italy analyze the sleeping and eating habits and gut health of 1,000 adult participants in a bid to understand the impact of “social jet lag” on diet and metabolic well-being.  

The research team included nutritionists and medical experts from King’s College London, the University of Nottingham, and Harvard T.H. Chan School of Public Health, with the study being carried out on behalf of Zoe, a British-American nutrition company.

As well as surveying participants about their sleep habits, experts analyzed their blood, stool, and food intake.

What is social jet lag?

Social jet lag was defined as “a pattern of sleep and wake times adjusted to workdays, and a shift in sleeping times on work-free days.”

Certain people are more prone to social jet lag, the paper’s authors noted, including adolescents and young adults, as well as those who are “biologically programmed for later bedtimes and wake times”—but they also stressed that “modern life with electric lights, blue-light emitting screens, and work schedules disturb normal sleep patterns.”

Study participants were divided into two groups: those who were experiencing social jet lag, and those who were not.

Study participants were sorted into the social jet lag group if their weekend sleep reached its midpoint more than one-and-a-half hours later than it did on a weekday.

Just 16% of participants were categorized as suffering from the phenomenon. In the wider world, the study’s authors said, it is thought that a much higher proportion of people are affected, with some estimates putting the figure at upwards of 40% of the population.

Social jet lag risks

The researchers found that their social jet lag cohort was younger, had a higher proportion of men, and had a shorter average sleep than the group with more consistent sleeping patterns.

They also noted that those with social jet lag were associated with “unfavorable diet quality”—meaning they ate fewer healthy plant-based foods than their counterparts, consumed more potatoes (including chips and fries) and sugar-sweetened drinks, and had a lower intake of fruits and nuts.

Social jet lag sufferers ate less frequently throughout the day and were more likely to delay their first meal, the findings also showed.

Meanwhile, associations were drawn between social jet lag and a poorer gut microbiome, with the findings showing that those with social jet lag were more likely to have a less favorable mix of bacteria in their gut.

Three of the six gut bacteria species that were more common in the social jet lag group were linked with poor diet, obesity, and increased risk of inflammation and stroke.

Meanwhile, higher levels of the hormone ghrelin—known as the “hunger hormone”—in the biological evening than the biological morning, coupled with jet-lagged participants’ disturbed circadian rhythm, increased their appetite for energy-dense foods, the paper said.

In order to improve nutritional choices and overall gut health, researchers recommended aiming to keep sleeping patterns consistent throughout the week, saying that achieving “sufficient sleep with consistent sleep-wake timing” was a potential lifestyle change that had the potential to reduce future risk of disease.

“The differences we have found suggest there may be an association of social jet lag with unfavorable health even under conditions of sufficient sleep,” they said in their paper. “As circadian rhythm is individualized, adjusting sleep to one’s biological clock is preferable but not always achievable in the context of social timing.”

They also noted, however, that further studies were needed to solidify their findings, and conceded there were various limitations to their study. These included the study’s design, limiting their ability to determine causality, as well as a lack of information on participants’ employment status and an inability to confirm whether participants used sleep medication.

Sleep deprivation and diet

Poor sleeping habits have previously been associated with overeating and unhealthy diets.

Various studies have linked insufficient sleep to an elevated risk of obesity, being more prone to eating high-calorie foods, and impaired appetite control.  

A 2016 study found that losing a few hours’ sleep per night was linked to consuming significantly more calories the following day—creating a cycle where poor food choices went on to damage sleep quality.

Further research has linked sleep deprivation to binge eating, with experts arguing that just one additional hour of sleep a night could lead to better eating habits.