Is eating weekend meals at different times than the week bad?

Earlier or later meal times — known as "eating jetlag" — is associated with an increased risk of cardiovascular disease among men — but not women, suggests the French study.

Work often requires people to adjust their eating patterns during the week, resulting in differences in eating schedules between weekdays and weekends or days off — when meal timing tends to be more closely aligned with their internal biological clocks.

But scientists say the shift — or eating jetlag — may disrupt the body's biological rhythm.

Previous studies have shown that disruptions to the biological clock linked to night work or late mealtimes can lead to cardiovascular complications, such as a heat attack or stroke.

The research team assessed the link between eating jetlag and the risk of cardiovascular disease by analyzing data from 104,806 adults participating in the NutriNet-Santé public health study between 2009 and 2023.

The severity of eating jetlag was calculated based on the timing of the participants' first and last meals of the day on weekdays and weekends.

The association between eating jetlag and the risk of cardiovascular disease was assessed using statistical models, which also took into account other factors including age, marital status and the number of children living in the household, smoking, alcohol consumption, physical activity, diet and sleep.

By comparing meal timing on weekdays and weekends, researchers from the National Research Institute for Agriculture, Food and Environment (INRAE) classified eating jetlag according to the magnitude of the difference into three categories.

"Advance" was where mealtimes were earlier at the weekend than on weekdays, with an average of two hours' advance in the eating window.

"Regular" was where the eating windows were similar, while "Delay" was where mealtimes were later at the weekend than on weekdays, with an average delay of one hour 40 minutes in the eating window.

The findings suggest that, for men, each additional hour of eating jetlag — be it earlier or later — is associated with an average 14% increased risk of cardiovascular disease and an average 21% increased risk of coronary heart disease.

Both the "Advance" and "Delay" groups showed a higher risk compared with the "Regular" group, according to the findings published in the journal Communications Medicine.

The research team didn't find any significant difference among women.

The researchers say the difference between men and women may be down to differences in physiological functioning between the two biological sexes or differences in lifestyle and work circumstances between women and men in society, which could lead to different circadian rhythms.

Study leader Bernard Srour said: "This initial study suggests that changes in mealtimes between weekdays and weekends may play a role in the development of cardiovascular disease, regardless of sleep and diet, particularly in men.

"A few years ago, we suggested that eating late was associated with an increased risk of cardiovascular disease.

"This new study suggests that, beyond simply eating late, maintaining consistent meal times between weekdays and weekends may be just as important.

"These associations appear to be independent of how long people sleep, suggesting that regular meal times could, in themselves, help resynchronize our biological rhythm."

Srour, research director at INRAE, added: "We are continuing our research to better understand this phenomenon.

”Further studies are needed to build on this initial observational study and establish the causality of these links."