Monday, May 08, 2006

Kicking the Pepsi Can: Hard truths about soft drinks

The latest study claiming that soft drinks are the driving force behind childhood obesity has prompted the usual silly responses. The aptly named Barry Popkin, an academic at the University of North Carolina, has mused about the need for tobacco-like surgeon general's warnings on soft-drink cans and bottles. Popkin's idea has been endorsed by Michael Thun of the American Cancer Society. Meanwhile, the misnamed Center for Science in the Public Interest continues to threaten legal action against the food industry based on the spurious claim that food advertising to children for products such as soft drinks is deceptive.

The much-headlined new study in the journal Pediatrics, from Boston's Children's Hospital, is a poor piece of research. Among its many limitations is that it studied a staggeringly small number of teenagers. A mere 103 teens were divided into two groups, an intervention group and a control group. The teens in the intervention group received home deliveries of noncaloric beverages (e.g., diet soft drinks, iced teas, lemonades, and bottled water) for 25 weeks in an effort to reduce soft-drink consumption. Not surprisingly, these kids reduced their pop consumption by a massive 82 percent.

Equally surprising, but unmentioned in every media report, was the fact that there was no statistically significant difference at the end of the six months between the Body Mass Index (the standard yardstick for obesity) of the group that the noncaloric beverages and the group that continued with their regular soft-drink consumption. In other words, an 82-percent reduction in soft-drink consumption did not make the kids thinner, which makes it difficult to see how this study indicts soft drinks as a principal cause of obesity.

The Boston study is also flawed by the fact that it failed to control for, or report on, any of the other aspects of the two groups' respective diets. We have no idea, for example, what the daily caloric intake was for any of the participants in the study. Without this information it is difficult to know, first, whether the two groups were in fact identical except for their soda pop consumption and, second, whether it was the elimination of regular soft drinks that really caused the small weight loss that was found in the most obese participants. Given that there are dozens of supposed risk factors for obesity, it is somewhat disingenuous to claim that removing one risk factor, without controlling for the others, suggests that the one removed is a cause of obesity.

What is really odd, however, about the Boston study is its simplistic assumption that there is a unique caloric effect that results from removing soft drinks from someone's diet. Removing any source of calories - whether from soft drinks or anything else - and not replacing them will result in fewer calories and perhaps fewer pounds. Does one really need an expensive research study to confirm something so blindingly obvious?

The real problem with this study is the fact that it is contradicted by most of the published scientific literature about the connection between soft drinks and childhood obesity. For example, a recent study which looked at the supposed link between obesity and diet in 137,000 children in 34 countries found that being overweight was not associated with the intake of soft drinks. This study confirmed research from Harvard University, published in 2004, that followed the eating habits of 14,000 children for three years. It found that there was no association between snack food consumption, including soft drinks, and weight gain.

Similar evidence was found by researchers at the Centers for Disease Control and Prevention just last year. They reported that, "Evidence for the association between sugar-sweetened drink consumption and obesity is inconclusive.[N]ational data showed no association between sugar-sweetened beverage consumption and Body Mass Index." In another study from 2005, which used data from the National Health Examination Surveys, the authors found no association between regular soft drinks and Body Mass Index, noting that regular sort drinks "accounted for less than 1 percent of the variance in Body Mass Index" among American children.

The media continues to give air time and column inches to obesity studies, especially those about soft drinks, so riddled with methodological flaws that their alarmist conclusions are worse than useless. All of which suggests that if the discussion about childhood obesity is going to be based on science, rather than science fiction, it needs to move beyond kicking the can.


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