Monday. According to a recent study by Orsama and colleagues, that’s the day when most people experience their maximum body weight. And your lowest body weight? That’s most likely to be recorded on Friday.
The weekend certainly seems to play some havoc on our energy balance.
The 7 day week cycle has an impact on many of our behaviors. Take sleep, for example. During the week, we get up regularly at the sound of our alarm, but come Saturday, the alarm clock may be turned off and you allow yourself to sleep in. Your physical activity level is also likely to oscillate based on the day; individuals who actively commute to work may become more of a couch potato on the weekend. People may also be more likely to go out and have a few drinks over the weekend. All these behaviors can have an impact on a person’s energy balance, and subtly, on their body weight. And apparently, that’s exactly what happens.
In the study published earlier this year, Orsama and colleagues explored the weekly rhythm of weight to understand the normal variation of weight which occurs during the week. The researchers analysed daily self-reported body weight in 80 adults (BMI: 20.0–33.5 kg/m2; age: 25–62 years). To avoid intra-day variation in body weight individuals were instructed to record their daily weight immediately after waking up and before breakfast. The length of each individual’s time series of recorded weight varied from 15 to 330 days.
As I’ve already summarized in the first couple of sentences, body weight tended to be highest following the weekend (Sunday/Monday) and lowest just before the weekend (Friday).
As a potential explanation of this weekly weight fluctuation, the authors propose that meal sizes and calorie intake tend to increase while physical activity tends to decrease during weekends. Indeed, many people who eat a clean diet during the week allow themselves a cheat day over the weekend. Evidence seems to favor such a flexible approach to diet management, by contrast to the all or none approach. The former approach allows you to enjoy some highly-favored but potentially calorie-dense foods in relative moderation, potentially increasing long-term adherence to a diet. By contrast, the latter approach, which outright forbids certain foods, may result in dietary boredom, and complete discontinuation of the healthy diet.
This also leads us to the other interesting finding in this study. Variation in body weight was also analysed according to whether the participants lost weight (greater than 3% reduction), gained weight (greater than 1% increase), or maintained weight (weight change between –3 and 1%). What is interesting, as illustrated in the figure below, is that the biggest fluctuation in weight occurred in those who lost weight over time. This would suggest that successful weight losers were allowing themselves some serious dietary leniency over the weekend. Maybe this is exactly what allowed them to persist on their respective diet for a longer duration.
What are the implications of this research?
First, if you like to regularly weight yourself, best to compare the same day of the week (and same time of day).
Secondly, allowing yourself a few indulgences over the weekend may in fact help you stick with eating better and managing your weight over the long term.
Orsama et al. Weight rhythms: weight increases during weekends and decreases during weekdays. Obes Facts. 2014;7(1):36-47. doi: 10.1159/000356147.