Do you ever find yourself on Monday wondering if you went a little overboard with the chips and dip over the weekend? And maybe even with those brownies at the party the weekend before? Oh yeah, and that “fourth meal” burrito from El Farolito Saturday night?

If you generally use weekends as an excuse to indulge a little, you are not alone. And according to a study published last month in Obesity, there is a good chance that weekend splurges are the reason you are gaining weight (or at least one reason it is so difficult to lose it).

Researchers at Washington University in St. Louis wanted to understand how weekends affect weight fluctuations in free-living individuals under different weight loss plans. To address this, they split participants into three groups and followed them for one year. One group was put on a calorie-restricted diet and another was given an exercise regimen. Both the calorie restricted and exercise group interventions were designed to create similar calorie deficits – 16-20 percent of total baseline energy expenditure for each individual – so that the effects of weight loss induced by each method could be compared. The third group was not given any intervention.

Because one goal of the study was to observe free-living individuals (i.e., people at home and not in a clinic), researchers utilized a comprehensive battery of measurements to determine energy intake, physical activity, energy expenditure, body composition and body weight. For instance, participants were provided with a special scientific scale that was collected at the end of each recording period. Body weights were then double checked on a calibrated scale in a clinic on several of the weight recording days. Duel-energy X-ray absorptiometry was used to measure body composition (lean mass versus fat mass) on multiple occasions throughout the study. Food diaries were kept by the participants to record daily food intake, and they received detailed instructions on how to weigh, measure and record everything consumed. Physical activity was measured with both triaxial accelerometers and urine samples using the doubly labeled water method.

Detailed documentation of variables and outcome measures is critical in experiments where people’s activity is not controlled in a laboratory, because self-reporting—particularly when weight loss and eating are involved – is notoriously unreliable. Though the methods used here do not guarantee accurate measurements, the double and triple validation that the scientists performed throughout the study certainly minimizes sampling biases.

The first interesting observations were found when scientists took baseline measurements during the 2-4 weeks before the experimental interventions began. During this period body weight at baseline increased significantly on weekends and was followed by a non-significant trend of weight loss on weekdays. Unfortunately this resulted in an increase of 0.077 kilograms (0.17 pounds) per week.

This increase may not sound like much, but it amounts to about 4.0 kilograms (9 pounds) gained per year. The authors of the study suggest that this finding may be an artifact of the anticipation individuals feel when beginning a weight loss regimen, because on average people gain less than 1 kilogram per year. Regardless, the finding that weight gain occurs on weekends and not on weekdays is significant.

Also during baseline measurements the researchers found that calorie intake was highest on Saturdays, averaging about 200 calories more than weekdays. Physical activity during this time was lowest on Sundays and highest on Saturdays.

During the experimental interventions, the weekend affect on body weight was still evident. As expected, both the calorie restricted and exercise groups lost weight over the course of an average week. On weekends, however, the calorie-restricted group stopped losing weight and the exercise group actually gained weight. The control group did not have significant weight changes on weekdays compared to weekends.

Interestingly, during the experiment all three trial groups consumed significantly more calories on weekends than on weekdays. Those on calorie-restricted diets ate more on Saturdays, while those on the exercise regimen consumed more on both Saturdays and Sundays. The control group ate more only on Sundays.

In contrast, physical activity did not decrease on weekends during the experiment. In the exercise group physical activity remained constant relative to weekdays. The calorie-restricted group actually increased activity on both Saturday and Sunday. In the control group there was a trend toward more physical activity on weekends.

These findings suggest that weekend behavior has a tremendous impact on weight gain in average people and makes weight loss more difficult for those undergoing a calorie restricted or exercise program. Furthermore, the weekend calorie imbalance is primarily caused by increased eating rather than decreased physical activity.

This research is consistent with that of the National Weight Control Registry report in 2004, which suggests that people whose diets are more consistent from weekdays to weekends are more likely to be successful in losing weight and keeping it off. It also agrees with two studies published in the International Journal of Obesity last month showing that human energy expenditure has not changed in America or Europe in the past 20 years and is still comparable to the amount spent by indigenous populations and even animals in the wild.

The bottom line is that while increased physical activity can aid in weight loss, excessive calorie consumption is the primary reason for weight gain in our time.

This story can also be found at Synapse.

Two interesting studies were published in the International Journal of Obesity this week. The first one examined how energy expenditure has changed in North America and Europe since the 1980s. It is generally assumed that the obesity epidemic is fueled partly by increased food intake and partly by a more sedentary lifestyle, but this assumption remains largely unproven. The present study aimed to directly measure energy expenditure, beginning when the technology to do so was developed (1980s).

Using three independent methods, the researchers show that energy expenditure has not decreased over the past two decades. In fact, people now use slightly more calories each day than we used to. But the authors of the study are quick to point out that energy expenditure and overall motor activity are not the same thing. This becomes clear in the second paper, which has one author in common with the first.

In the next study, scientists measured the correlation between motor activity and body composition (body fat %). They report that indeed higher body fat percentage is correlated with decreased locomotion. If you look closely, this does not contradict the first paper.

The difference between the two studies is that one measures locomotion (movement) and the other measures energy expenditure directly, independent of movement. Locomotion is related to total energy expenditure, but the relationship is highly dependent on the body mass of the individual. To put it plainly, bigger people use more energy to do the same activity as smaller people. So while it is clear that obesity is associated with moving less, these individuals are generally burning the same number of calories as leaner individuals who move more.

Even more telling is that the amount of energy people use in North America and Europe is similar to the amount used by native, indigenous populations and also animals in the wild. This makes it very difficult to argue that decreased energy expenditure is contributing to the obesity epidemic. So what is truly fascinating about these two papers is the conclusion that can be drawn about the cause of obesity: we are eating too much.

Evidence is mounting that people in Western cultures are vastly underestimating their energy intake, which is causing a tremendous rise in obesity prevalence. Based on this information it seems like dietary habits should be the first point of intervention if we want to reverse this trend.

Thoughts?

A recent study published in the journal Cell describes a chemical that has the ability to increase exercise endurance in mice without a regular exercise regimen (i.e. training). News media has paraded this research as the discovery of an “exercise pill” that could potentially reduce or eliminate the need for regular exercise.

If this sounds a little ridiculous to you, you are not alone.

I am happy to report that not everyone interprets this new data as the answer to America’s obesity epidemic. An article appeared in today’s ScienceDaily explaining that the research does not even come close to testing all the potential benefits of exercise and therefore extreme caution should be taken when interpreting the results of this single study.

Benefits of exercise that were not tested in the mouse study include (but are not limited to) increasing positive measures of cardiac capacity and decreasing risk for diseases like heart disease, hypertension, type 2 diabetes, breast cancer, colon cancer and osteoporosis.

So let’s be clear: there are countless benefits of exercise and we have no idea if this substance can replicate them or not.

It is also good to remember the pure physical enjoyment and heightened quality of life that can be achieved through exercise, valuable outcomes that scientists often neglect in their analysis.

And did I mention this study was done on mice and not humans?

Such research may one day improve the lives of individuals who have the misfortune of a physical handicap that prevents or limits regular exercise. For the rest of us, my advice is to find ways to make exercise fun and enjoyable rather than hoping science can give you an excuse for getting out of it.

What do you think about an “exercise pill”?