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New Study: Weekends Mean Weight Gain for Many Dieters

By L.K. Regan

This will come as no surprise to some, but a new study has found concrete proof that weekends are seriously damaging to diets. Researchers at the Washington University School of Medicine in St. Louis, Missouri found that people on a calorie restricted diet or an exercise program did not lose as much weight as anticipated—because of their eating habits on the weekends. Worse yet, the group with an exercise program gained more weight than the group on straight calorie control. And, not surprisingly, Saturday is the worst day for the waistline.

The Washington University researchers were conducting a larger project to determine the impact of a calorie-restricted diet over a long period of time. Studies in mice and rats have demonstrated that reducing caloric intake can substantially improve health and longevity. This study investigated the effects of calorie restriction on humans, hoping to find that by reducing energy intake, we can reverse some of the effects of aging and disease. Hence, Washington University's CALERIE (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy) study. As part of observing the outcomes of calorie restriction on subjects, researchers noticed a marked effect in weight-loss patterns: that subjects kept gaining weight on the weekends.

The study's first author, Susan Racette, an assistant professor of physical therapy and of medicine, was astonished by the results. "We thought weekends would present a problem for some people attempting to lose weight, but the consistency of our finding before and during the interventions was surprising. Subjects in the diet group lost weight during the week, but over the weekend, they stopped losing weight because they were eating more." This finding is the first to demonstrate short-term oscillations in weight loss of the sort most commonly seen across the year, as people gain weight over the holidays. Now, it turns out, this is a weekly event.

The study followed 48 adults and divided them into three groups. One group reduced their caloric intake by 20 percent, another increased their daily exercise, and a third changed nothing. All three groups were tracked for a year, with food diaries, daily weigh-ins, and accelerometers to measure calorie intake and expenditure. But before the participants even began following the study's program, the researchers took baseline measurements of their eating habits and daily caloric intake. And they found that, before the study began, all of the subjects were eating enough additional calories on the weekends to account for an average weight gain of nine pounds per person per year! Saturdays alone accounted for fully 36 percent of weekly calories.

Once subjects began the study, this effect did not go away. Those subjects on calorie-restricted diets still ate additional calories on Saturdays, and stopped losing weight on that day. And the exercise group ate more calories on Saturday and Sunday alike, and actually gained weight on the weekends.

Researchers feel that this result can explain why, as Racette puts it, "People on diets often don't lose as much weight as we would expect." In fact, subjects were often completely unaware that they were eating more on weekends, meaning that people typically do not understand why their diets are failing.

As a result, the researchers' recommendations are fairly intuitive. Since weekends are full of unexpected activities away from home, which may lead to eating on the fly, try to plan ahead. Pack snacks when you're going to be away from home for a while; eat a little something before a party so you don't gorge yourself; bring a basket to the game so you don't hit the concession stand; and so on. And, Racette warns, be very aware of portion size.

But also be prepared to let your belt out a hole on Monday.