In a nutshell: a study was conducted with overweight preteens. Some were given a book with an unhappily overweight protagonist. Others were given a book with a normal-weight protagonist. A third group wasn't given any book.
There are a number of things it doesn't take into account. Losing weight includes lifestyle changes that (especially for kids) never exist in a vacuum. Case in point:
For the study, the Duke University researchers recruited 31 obese girls between 9 to 13 years of age, who had already signed up in the Healthy Lifestyles Program at Duke Children's Hospital. Italics mine.These were girls who already wanted to make a positive change in their health (or their parents wanted them to). It's not as if they plucked kids off the street and changed their entire outlook on life with one book.
In a telling omission, it touts the 71% statistic of kids who read the first book, but doesn't mention the change in weight for the other two groups.
It may be the writing of the article that makes it sound like one book was the deciding factor, but to me, this study is reducing children's lit to manipulation, and children themselves to paper dolls.