A new study adds to the evidence that maintaining a regular eating schedule is key for preventing obesity.

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Eating at irregular times during the weekend may eventually lead to weight gain.

For many, the end of the workweek brings a welcome respite from the rigid scheduling of workdays.

It offers a taste of freedom: a few days of a more fluid schedule or no schedule at all.

A new study, however, finds that a more improvised weekend eating schedule may link to an increase in body mass index (BMI).

The study’s authors refer to people’s weekend diversions from their regular eating schedule as “eating jet lag,” which they suggest may be as physiologically disruptive as the body confusion that can occur when traversing time zones.

The cross-sectional study is part of the doctoral thesis of first author María Fernanda Zerón Rugerio of the University of Barcelona (UB) in Spain.

The paper, which other UB researchers co-authored, appears in the journal Nutrients.

The authors analyzed data from 1,106 undergraduate and postgraduate students between the ages of 18 and 25 years who reported their weekend eating schedules during the school year.

The study ran from 2017 to 2019. Each participant also self-reported their height and weight — the two measurements that make up BMI.

The study’s authors believe that this is the first study to focus on the effect on obesity of changes in meal timing between weekdays and weekends.

From the students’ responses, researchers were able to determine the cohort’s average meal duration during the week and on the weekends, as well as the eating midpoint — halfway between the first and last meal of the day — for both weekdays and weekends.

To calculate an individual’s overall eating jet lag value, they used a simple formula: eating midpoint on weekends minus eating midpoint on weekdays.

From there, the researchers accounted for other influences that could affect BMI, including diet quality, sleep duration, gender, and chronotype.

The authors found that those with an overall eating jet lag of 3.5 hours or more had higher BMI values.

They used the same formula to calculate the separate eating jet lags for breakfast, lunch, and dinner.

Not surprisingly, given the opportunity to sleep in at the weekend, the meal that exhibited the greatest amount of jet lag was breakfast.

The study showed that 64% of participants experienced more than an hour of breakfast-eating jet lag each weekend, with this duration exceeding 2 hours for 22% of these individuals.

The researchers did not detect any correlation between the eating jet lag for a particular meal and a higher BMI.

Eating jet lag may stem from the same sort of conflict between a body’s circadian rhythm and unusual activity as other forms of jet lag — the sleep disruption that travelers experience — and “social jet lag” resulting from unusual weekend sleeping schedules.

As the study authors put it, “The circadian system is comprised by a master clock and a network of peripheral clocks, all of which are organized in a hierarchical manner.”

One of the study authors, Trinitat Cambras of UB’s Department of Biochemistry and Physiology, explains further: “Our biological clock is like a machine and is ready to unchain the same physiological and metabolic response at the same time of the day, every day of the week.”

“Fixed eating and sleep schedules help the body to be organized and promote energy homeostasis.”

Lead author Maria Izquierdo Pulido of UB’s Institute for Nutrition and Food Safety ties the biological clock to the way in which the body processes food:

“As a result, when intake takes place regularly, the circadian clock ensures that the body’s metabolic pathways act to assimilate nutrients. However, when food is taken at an unusual hour, nutrients can act on the molecular machinery of peripheral clocks (outside the brain), altering the schedule and thus, modifying the body’s metabolic functions.”

– Maria Izquierdo Pulido

There is still a need for more research regarding the link between eating jet lag and BMI.

Still, points out Izquierdo Pulido, it is already known that maintaining a regular schedule has benefits. Scientists may now add combatting eating jet lag to these.

She says, “Apart from diet and physical exercise, which are two pillars regarding obesity, another factor to be considered is regular eating schedules, since we proved it has an impact on our body weight.”