The age group of the children studied typically experience major changes in body type and body mass index, and the sample does not represent a valid cross section of the American population. The prevalence of obesity among American children increased by 100 percent from 1980 to 1994. A common measurement of obesity is body mass index, which takes into account weight and height. A measurement of 25 means a person is overweight. The threshold for obesity is 30.
Experts disagree on what constitutes obesity in children.
The study used the 85th percentile as the threshold for obesity. By that measure, scientists estimate that 24 percent of American children are obese. The soft drink study involved keeping track of 548 children age 11 or 12 from public schools across Massachusetts for two school years, ending in May 1997. It found that if children increased their daily intake of soft drinks, each extra drink made them 60 percent more likely to become obese, regardless of how many such drinks they were consuming before. Fifty-seven percent of the children increased their intake of soft drinks over the two years, with a quarter of them drinking two or more extra cans a day, the study said.