Methods: The daily weight in 80 adults (BMI 20.0-33.5 kg/m2; age, 25-62 years) was recorded and analysed to determine if a group-level weekly weight fluctuation exists. Results: A pattern of daily weight changes was found (p < 0.05), with higher weight early in the week (Sunday and Monday) and decreasing weight during the week. 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%). “The big difference between those who gain weight over time and those who lose or maintain weight is directly related to the way they eat from Monday to Friday," said Cornell University behavioral economist Brian Wansink, one of the study authors. The takeaway 
 
 Long-term habits may make more of a difference than short-term splurges, the study authors say. Menstrual cycles are an example of biological monthly rhythms. The 7-day cycle of a week also has a strong impact on life [13] that is more environmental and behavioural than biological. Material and Methods 
 
 Retrospectively Collected Weight Data 
 
 Self-recorded weight measurements were aggregated from four earlier data collection efforts [18,20,21,22] in which individuals were instructed to self-monitor and 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. 1 
 
 Day of the Week Effect 
 
 The first hypothesis involved testing whether the day of the week had a linear effect on weight when starting from Sunday, or whether the expected weight is constant and does not depend on the day of the week. The minimum weight of the week was most frequently observed on Friday and, in 60% of the cases, the week's minimum weight occurred either on Friday or Saturday. 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. on Sunday and Monday, and decreased toward the end of the week. Also important to note is that the researchers are talking about slight caloric increases. The participants were grouped according to their weight changes over the study period: weight losers who lost at least 3% of their body weight; weight gainers who put on at least 1%; and weight maintainers who stayed in between those minimums. 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. 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). Similar findings can be seen in the research of Racette et al. Weight loss success depends primarily on your ability to compensate for those splurges on other days of the week. Allowing more flexibility on weekends and holidays might be more realistic from a long-term perspective because it avoids dietary boredom [35]. Despite this low threshold, our sample size of the GAIN group was small, which limits the generalizability of the results and highlights the overall challenge of learning more about weight gainers. Due to the small sizes of GAIN and LOSS groups (10 and 18 individuals, respectively), the suggested relationship between the weekly rhythm and weight management success should be considered preliminary. The findings of this study suggest that weight should not be expected to be constant throughout the week. And a flexible eating pattern - i.e., allowing yourself that brownie or beer on Friday night - may help you sustain overall healthy eating habits over time. “There is a clear weekly rhythm to weight variation for most people,” says one of the study authors, Anna-Leena Orsama, a research scientist with VTT Technical Research Center of Finland. “On the weekends there is more variability and unpredictability in what we eat.” 
 
 The study, “Weight Rhythms: Weight Increases during Weekends and Decreases during Weekdays,” was published this week in the journal Obesity Facts. Additionally, there is preliminary evidence that those people who show the largest compensating change from the weekend to the weekdays are those who - over time - are most likely to either lose weight or maintain their weight. Our results provide scientific support to the tenet that in weight management, allowing more flexibility during weekends and holidays might be more realistic and successful in the long term than a strict regimen.
– For most of us, weekends are a time to relax and indulge—maybe through more sleep, more couch time, or more calories in the food and beverages we consume. The result is that we tend to weigh slightly more on Sunday and Monday, but then slightly less again by Friday, reports the Smithsonian. And enough of us do this that scientists say they've observed the general weight trend in a small study published in the journal Obesity Facts. The researchers analyzed the recorded daily weights of 80 adults ages 25 to 62 and found weight "increases begin on Saturday and decreases begin on Tuesday." Before we all fall into a pit of despair in the days leading up to Thanksgiving, one doctor stresses on PLOS' Obesity Panacea blog that it's not a bad thing to "cheat" diets and habits on the weekends. In fact, it "allows you to enjoy some highly-favored but potentially calorie-dense foods in relative moderation, potentially increasing long-term adherence to a diet." The study's authors agree, telling CNN that "some indulging" does no harm. (Meanwhile, if you want to lose weight, research indicates you shouldn't forgo fats.)