Soft Drinks, Hard Facts

Reporting in The Lancet, a British medical journal, a team of Harvard researchers presented the first evidence linking soft drink consumption to childhood obesity. They found that 12-year-olds who drank soft drinks regularly were more likely to be overweight than those who didn't. For each additional daily serving of sugar-sweetened soft drink consumed during the nearly two-year study, the risk of obesity increased 1.6 times.

Could it be that the soda pop drinkers were simply living extremely sedentary lives? Or that they ate more than the kids who didn't drink soft drinks regularly? When lead author David Ludwig and his colleagues parsed the data to examine those possibilities, neither explanation panned out. Drinking soda proved to be "an independent risk factor for obesity," says Ludwig.

The soft drink industry quickly took steps to dispute the findings. Although the study included 548 ethnically diverse youngsters attending four public schools in Massachusetts, the NSDA knocked the research for including too few Caucasian kids: About two-thirds of participants were white, compared with 75 percent of the total U.S. population and 88 percent of Massachusetts residents.

The industry response also cited an earlier study conducted by Georgetown University's Center for Food & Nutrition Policy that showed overweight children consumed about 14 ounces of carbonated beverages per day -- only about two ounces more than kids of normal body weight. The Sugar Association paid for part of the Georgetown study, which was presented last April at the Experimental Biology 2000 meeting, but it has not been published in a peer-reviewed journal.

Obesity experts, on the other hand, called the Harvard findings important and praised the study for being prospective. In other words, the Harvard researchers spent 19 months following the children, rather than capturing a snapshot of data from just one day. It's considered statistically more valuable to conduct a study over a long period of time.

But even those who lauded the Harvard report still underscored the usual caveats. "It's only a single study, and it needs to be repeated," says William H. Dietz, director of the division of nutrition and physical activity at the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta.

If soft drinks do prove to contribute to obesity, how might this happen? Is it simply a matter of drinking in too many calories?

Again, the jury is out, and there are several competing theories. But there are some tantalizing clues suggesting that excess calories alone can't explain the problem. The Harvard team also conducted a meta-analysis -- a number-crunching examination of similar research conducted over the past 25 years -- to explore this question. They concluded that drinking sugary calories doesn't register with the brain the same way that eating calories does. In other words, the brain seems to get confused by these sugary liquid calories that pass quickly through the stomach; they do not seem to trigger feelings of satiety in the same way calories from foods do. Absent a signal that calories have been consumed via soft drinks or sweetened fruit juices, the stomach does not tell the brain to quit eating at the current meal or to eat less at the next meal. In this way, the thinking goes, excess pounds are added.

Ludwig found that schoolchildren who drank soft drinks consumed almost 200 more calories per day than their counterparts who didn't down soft drinks. That finding helps support the notion, he says, that "we don't compensate well for calories in liquid form."

The soft drink industry doesn't buy that conclusion. "Childhood obesity is the result of many factors. Blaming it on a single factor, including soft drinks, is nutritional nonsense," noted Richard Adamson, NSDA's vice president for scientific and technical affairs.

On this point, the obesity experts tend to agree: "There are no data from the Harvard study that allow us to make an estimate of what proportion of obesity might be accounted for by changes in soft drink consumption," says the CDC's Dietz. "It's unlikely that we will be able to tie the obesity epidemic to any single change in the way we live. It is much more complex than that."

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