A new study by the University of Barcelona (UB) concluded that irregularity in eating schedules during the weekend, named by the authors as eating jet lag, could be related to the increase of body mass index (BMI), a formula that measures weight and height to determine whether someone's weight is healthy.

These results, published in the science journal Nutrients, were independently taken from factors such as the quality of the diet, level of physical activity, social jet lag (difference in sleeping schedules during weekends) and chronotype (natural predisposition to a certain sleeping schedule).

According to the researchers, this is the first study that shows the importance of regularity in eating schedules -including weekends- to control weight, and could be an element to consider as part of nutrition guidelines to prevent obesity.

The study, jointly led by Maria Izquierdo Pulido, from the Department of Nutrition, Food Sciences and Gastronomy of the UB and INSA-UB, and Trinitat Cambras, from the Department of Biochemistry and Physiology of the UB, is part of the doctoral thesis of the researcher María Fernanda Zerón Rugerio, first author of the article. Other participants in the article are Álvaro Hernáez, from the August Pi i Sunyer Biomedical Research Institute (IDIBAPS) and the Physiopathology of Obesity and Nutrition Networking Biomedical Research Centre (CIBERobn), and Armida Patricia Porras Loaiza, from Universidad de las Américas Puebla (Mexico).

The importance of the biological clock in nutrition

During the last years researches proved the body understands calories differently depending on the time of the day. Eating late can be related to a higher risk of obesity. According to Maria Izquierdo Pulido, "this difference is related to our biological clock, which organizes our body to understand and metabolize calories consumed during the day". At night, however, "it gets the body ready for fasting while we sleep".

"As a result -the researcher continues-, 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".

The new study was carried out on a population of 1,106 young people (aged between eighteen and twenty-two) in Spain and Mexico. Researchers analyzed the relation between the body mass index and the variability in eating timing during weekends compared to the rest of the days. To do so, authors used a new marker that gathers changes in eating times (breakfast, lunch and dinner) at weekends: the eating jet lag, presented for the first time in this study.

Our results show changing the timing of the three meals during the weekend is linked to obesity. The highest impact on the BDI could occur when there is a 3.5-hour difference in eating schedules. After this, the risk of obesity could increase, since we saw individuals who showed a 3.5-hour eating jet lag increased their BDI in 1.3. kg/m2. María Fernanda Zerón Rugerio, first author of the article

Lack of synchrony between the social and body time

To explain the link between eating jet lag and obesity, authors suggest individuals to undergo a chronodisruption, that is, a lack of synchrony between internal time of the body and social time. "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. Therefore, people with a higher alteration of their schedules have a higher risk of obesity", notes Cambras.

More research is needed to reveal the physiological mechanisms and metabolic alterations behind the eating jet lag and its link to obesity. However, authors highlight the importance of keeping regular eating and sleeping schedules to preserve health and wellbeing. "Apart from diet and physical exercise, which are two pillars regarding obesity, other factor to be considered is regular eating schedules, since we proved it has an impact on our body weight", notes Izquierdo Pulido.

Studying the long term effects of eating jet lag

The study notes the importance of doing research on the relation between time irregularity and the evolution of weight over time, as well as conducting the study on populations with different social and economic characteristics, metabolic features and different age. "Variability in eating schedules during weekends compared to week days can happen chronically during someone's life. Future studies should evaluate the effect of this chronic variability through the eating jet lag, on the evolution of weight", conclude researchers.