New research published Feb. 3 in the European Journal of Obesity, Obesity Facts, has revealed for the first time that the influence of the week's eating, sleeping and activity cycle has a pronounced and quantifiable effect on weight. The week's cycle influences sleep, exercise, and eating habits. The effect on weight has, until now, not been investigated. The study found that people begin to gain weight on a Saturday and to lose weight on a Tuesday, each week.
The researchers discovered that practically everyone gains weight on the weekends, but loses weight on weekdays. The results revealed a clear pattern in weekly weight fluctuation with higher weight after weekends (Sunday and Monday) and decreasing weight during the weekdays reaching the lowest point on Friday. The difference between slim people and overweight people is how much weight they lose, on average, during the weekdays, with the amount gained over the weekend being less important.
In this study, Dr. Brian Wansink from Cornell University, in collaboration with researchers from the VTT Technical Research Centre of Finland and Tampere University of Technology, investigated the impact that the human cycle of a 7-day week has on weight.
The study involved 80 adults aged between 25 and 62 years of age with a Body Mass Index or BMI of between 20 and 33.5, which encompasses all categories from normal weight, to overweight and even obese. The study included people who tended to gain weight, those who tended to lose weight and those who tended to simply maintain a constant weight. The weight of each person was recorded daily over a period of almost one year and analysed to determine whether any patterns existed within the group as a whole.
Body Mass Index
Normal: 18.5 - 24.9 kilograms per meter squared
Overweight: 25.0 - 29.9 kg/m2
Obese: 30.0 - 35 kg/m2
Calculate your BMI by dividing your weight in kilograms by your height in meters squared
Obesity is a powerful, prevalent predictor of poor health and one of the key challenges facing an increasingly affluent society. In 2010, 475 million adults worldwide were obese. By 2030, that figure is expected to have grown to 1,115.8 million adults worldwide.
Obesity is behind many of the diseases which top the mortality tables. The risk of type II diabetes, cardiovascular disease, osteoarthritis, gallstones, colon and breast cancer and even the incidence of mental disorders is increased in the obese.
Once viewed as a simple imbalance between energy intake and expenditure, obesity is now recognised to be a far more complex condition, influenced by the actions of many hormones discovered in recent decades.
The behavioural habits humans have adopted as part of a daily, weekly and seasonal pattern and influences from environmental factors have long been known to affect various biological processes including body temperature, blood pressure, glucose metabolism and even menstrual cycles. Disruptions in these rhythms can increase the likelihood of developing diseases such as type II diabetes.
The study participants were asked to weigh themselves after waking up before breakfast. Only weight measurements that were taken over at least seven consecutive days were included in the analysis. The minimum follow-up time was 15 days and maximum 330 days.
Unexpectedly the researchers found a difference between weight losers and weight gainers in these fluctuation patterns. Weight losers had stronger compensation pattern (i.e. after weekend the decrease started immediately and continued downward until Friday) whereas weight gainers had more variability between days and no clear decrease during weekdays. Weight losers reached week’s maximum weight in 59% of cases on Sunday and Monday and week’s minimum weight in 60% of cases on Friday or Saturday. Among weight gainers no such a pattern was seen. Minimum and maximum weights did not systematically appear on certain days but they were evenly distributed all over the week.
Based on these results, weight variations between weekdays and weekends should be considered normal instead of weight gain. On the weekends people have more time to go out and eat. Some indulging during weekends makes no harm but for successful weight loss it is important to notice these rhythms and take steps to reverse the upward trends after the weekend, even if it has to wait until Monday. Successful weight control is more likely to happen and for the long run if one is not too strict with one’s diet but allows for short-term splurges. The day-to-day routine during the week appears to be of far greater significance to weight management than the degree of indiscretion and excess indulged upon over the weekend.
Orsama, Anna-Leena. (2014--1--1) Weight Rhythms: Weight Increases during Weekends and Decreases during Weekdays. , 7(1), 36-47. DOI: 10.1159/000356147