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Weight rhythms: Weight increases during weekends and decreases during weekdays

Orsama, A., Elina Mattila, Miikka Ermes, Mark Van Gils, Brian Wansink, and Ilkka Korhonen (2013). Weight rhythms: Weight increases during weekends and decreases during weekdaysObesity Facts,  7. doi:10.1159/000356147.

Miikka Ermes , ‎Senior Scientist (Digital Health) at VTT / Visiting Scholar at Flinders University

Understanding of the mechanism of weight gain outside of “calories in, calories out” is limited. A better understanding of weight gain patterns could provide insight as to how to prevent and treat obesity. One hypothesis is that there is some rhythm analogous to a circadian rhythm or menstrual cycle that could be the driver of debilitating weight gain. Past research has indicated that weight tend to be higher on weekends and lower on weekdays, but it is unclear if this phenomenon is related to long-term weight management. The purpose of this study is three fold: to find evidence that indicates whether there is a group level variation in weight fluctuation over a week, to study the relation of weight change to the days of the week, and to study how weekly weight patterns affect weight losers, gainers, and maintainers. 

To study weight variation across days of the week, self-recorded weight management data was collected from 178 subjects. To avoid bias, only measurements that were taken after waking up and before breakfast on seven sequential days were used. These restrictions resulted in 80 individuals being included in the analysis, with time series varying from 15 to 330 days. The participants were broken up into segments based on the kind of weight variation they exhibited: maintain weight (-3% to 1% change), lose weight (-3% change), and gain weight (+1% change).

An initial weight profile was constructed from the average weight on each day of the week among the three groups. Based on this model, additional, different models were set up for each of the three sub groups. Researchers used these data to determine whether day of the week had a linear effect starting from Sunday or if it was constant and there was no dependence on the day of the week.

The results showed that 60 % of the week’s minimum weights, occurred on Friday or Saturday and 59% of the week’s maximum weight occurred on Sunday or Monday. The gainers and maintainers groups showed more variability; the minimum and maximum weight mostly occurred on Monday, but the distribution on other days of the week was similar. Individual-specific trajectories were added to the population models to decrease the unexplained variability in the weight data but the data maintained the same trajectory.

 Based on these results, we found that there is a weekly weight rhythm with weight being highest on Sunday and Monday and reaching a low point on Friday and Saturday. Rhythm profiles also illustrated differences within the three weight management groups. The weight losers and weight maintainers showed a slight increase towards the end of the week when compared to the weight gainers. Explanations for these trends include the fact that people tend to have more leisure time to eat on the weekends, which proves consistent with studies that explore the effects of a weekly schedule on human behavior. In addition, physical activity also tends to be higher on the weekdays. Those who showed the greatest compensating change from weekend to weekdays are those who had most likely either lost or maintained weight. Long-term habits, it appears, make more of a difference than short-term splurges. In conclusion, the results of this study indicate that weekend weight gain is a normal pattern that does not necessarily contribute to long-term weight gain as long as individuals compensate for weekend weight gain during the weekdays. Researchers recommend allowing more flexibility in diet around holidays and weekends since weight gain is related more to long-term eating patterns than short term splurges.