Junkfood Science: Another study from the alternative universe that is the war on obesity

March 07, 2008

Another study from the alternative universe that is the war on obesity

There is nothing wrong with your television. Do not attempt to adjust the picture. We are now controlling the transmission. We control the horizontal and the vertical. We can deluge you with a thousand channels or expand one single image to crystal clarity and beyond. We can shape your vision to anything our imagination can conceive. For the next hour we will control all that you see and hear. You are about to experience the awe and mystery which reaches from the deepest inner mind to the outer limits. — The Outer Limits (1963-1964)

Que the scary music....

We’ve all heard the news this week reporting on a new study purportedly showing that restricting time in front of the television helps children lose weight. Dr. David Katz, director of the Yale University School of Medicine Prevention Research Center and the Integrative Medicine Center (probably best known among consumers for his online weight loss plan and monthly columns for Oprah’s magazine), told Forbes that this study shows that less screen time can help prevent childhood obesity and “highlight[s] the importance of this strategy.” This was echoed by Steven L. Gortmaker, Ph.D. of Harvard School of Public Health in an editorial in the journal Archives of Pediatric and Adolescent Medicine who opined that this study provides “evidence that television watching and other screen time are important modifiable causes of childhood obesity.”

Did this study actually support the popular vision of our children lethargically slumped in front of television and computer screens growing fat and listless? The study did involve televisions and children, but that’s where any similarities to the news ended.

Study design

This trial, led by Leonard H. Epstein, Ph.D., of the Behavioral Medicine Laboratory at State University of New York at Buffalo, recruited through newspaper advertisements, flyers and direct mailings 185 families with young children 4 to 7 years of age who wanted to participate in a study to test restricting screen time for the prevention of childhood obesity. Of those families, 115 were eliminated or withdrew, leaving 70 who agreed to have a usage monitoring and control device, called a TV allowance, installed on their televisions and computer monitors. To be included in this study, the children had to be healthy with BMIs at or above the 75th percentile for their age and gender.

The families were randomized into an intervention group and control group, but were not blinded. In other words, the parents in the intervention group knew that they were testing reduced screen time for its weight loss effects. The 36 parents in the intervention group were instructed to praise their children for watching less television and doing alternative activities that would reduce sedentary behaviors. The parents in the intervention group were also given ideas for physically active behaviors to encourage, information on how to change the home environment to reduce access to sedentary behavior, and monthly newsletters with parenting tips and recipes. Their children were paid 25 cents for each half hour under their allotted screen time they used and could earn up to $2 a week. Each month, the children’s screen time allowance was reduced 10% until it was cut in half. Children in the control group had their screen time monitored but were allowed to watch unrestricted and received $2 a week for participating, regardless of their behavior change. Their parents received the monthly newsletters with tips and recipes, too.

Physical activity was monitored in all of the children by wearing accelerometers and random recordings were taken during 3 weekdays after school and one weekend day. The calories the children consumed were monitored by their parents and recorded using an 85-item food frequency questionnaire completed by a parent.

Screen time in the intervention group dropped to 7 hours per week and then stayed the same (a straight line) for the remainder of the 2-year study period. So, the researchers maintained good compliance with reduced screen time during this trial. Screen time in the control group had been higher than the control group before the study began and lowered slightly to around 11 hours/week during the first 18 months of the study.

But the reduced screen time in the intervention group did not translated to any increase in physical activity. There was no difference in the physical activity levels between the groups. As the researchers noted: “No statistically significant between-group changes over time were observed for changes in physical activity.”

This is exactly what has been shown time and again, as was reviewed in “The Telly Tubby Myth.” Sedentary activity and physical activity are not two sides of the same coin. Kids engaged in the most sedentary activity are often the same ones engaged in the most physical activity. Turn off the television and they’ll still hang out and read, play board games, talk to their friends, work on models, whatever — things a lot of them were probably doing with the television on anyway and that kids have done generations. Data from the Youth Risk Behavioral Surveillance System of the U.S. Centers for Disease Control and Prevention, and a review of the evidence for children’s physical activity in the U.S. and internationally, conducted by Adelaide, Australian researchers, for example, concluded that the evidence does not support the view that young people are less active today. Population data shows little, if any, change for decades. In fact, trend data actually suggests dramatic increases since the 1960s in extracurricular sports and physical activities. There is little empirical support for the belief that reduced physical activity or increased television and computer time are responsible for childhood “obesity.”

At the end of two years, even while screen time stayed the same and physical activity didn’t increase in the intervention group, the relative BMIs of the kids dropped.

This led to news reports saying: “Blocking kids from televisions and computer screens could help them lose weight!” And the researchers concluded: “Reducing television viewing and computer use may have an important role in preventing obesity and in lowering BMI in young children.”

Are there magic fat rays emanating from television sets that might explain this?

Or might there be a more rational explanation?

A closer look

First of all, at the end of the 2 year study, the relative BMIs of the children in the intervention group had decreased by a mere 0.24, compared to the control group’s decrease of 0.13 — about one-tenth of a BMI unit difference in two years. There was also only a statistically significant difference during the first 12 months of the study. There was no change in the number of children in the “at risk for overweight” or “overweight” percentiles. This negligible effect hardly deserves the fanfare it has received, but we should be glad the children’s relative BMIs didn’t fall more.

These were healthy, growing children who were only 4-6 years old when the study began. Drops in relative BMIs mean children are falling off of their growth curves. Children who fall off their growth curves are not growing normally, in line with how they should to ensure proper development. There is no evidence that this is a healthful thing for children. By reporting BMIs, rather than their actual heights and weights, it is impossible to know how much the weights in these young children may have become disproportionately below ideal for their heights.

When trying to figure out why their BMIs dropped even while their levels of activity stayed the same — we’ll disregard the woo theory of magic TV fat rays — we see that as the trial progressed, the parents in the intervention group were especially feeding their preschool and elementary school children fewer and fewer calories for 18 months. Since it was not a blinded study, it seems the parents in the intervention group believed their kids should have been losing weight and basically put their kids on a diet. By 18 months, the growing children in the intervention group were being underfed by nearly 400 kcal per day from what they had been eating at the beginning of the study. This was considerably less than the caloric changes seen in the control group, which were more in line with what is normal for this age group.

The families in this study were also not your typical families, but were self selected. According to the USDA/ARS Children’s Nutrition Research Center calorie recommendations for children (which are the recommendations used by the 2005 Dietary Guidelines), these children for their ages, BMIs and activity levels at the beginning of the study needed an average of 1,885 kilocalories a day, but were getting an average of 1,560 kcal/day, indicating either miscalculations by the researchers, or, more likely, that this study recruited parents already concerned about their children’s weights. All the focus on the children’s daily activity, calories and screen time appears to have led the parents to be increasingly more focused on their children’s weights and diets, and feed them even less.

The researchers attempted to do a secondary analysis of their BMI data by socioeconomic status, but failed to provide breakdowns for caloric intakes, making any interpretations impossible.

Bottom line: The relative BMI loss, as practically insignificant as it was, only paralleled the degree to which the children had been underfed — with no correlation to screen time. Like all diet studies, even this minuscule loss has almost no probability of being sustained long-term.

This study provides no support for reducing screen time as a way to prevent childhood obesity. Nor does it support “a role for these gadgets in helping make children more active,” as Tam Fry, chairman of the Child Growth Foundation, said.

We now return the control of your television set to you...

© 2008 Sandy Szwarc

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