NBER recently released two somewhat related papers that is very interesting. First, having overweight children is actually worst than it is. Susan Averett, Hope Corman and Nancy Reichman found that "overweight or obese teenage girls are more likely than their recommended-weight peers to engage in certain types of risky sexual behavior but not others." I think it's actually sad because the way I see it, obese children may be aware of stigma associated with being fat (less attractive, etc.). So I suppose engaging in sexual activities makes them feel better about themselves. I'm not making excuses for them. In fact, I think this paper is one reason for parents to control their children's excessive eating behavior.
Related to obesity is Christopher J. Ruhm's paper pointing out that obese children may not be thinking rationally when they're binge-eating. Being a rational person, you would be aware of the negative effects of being obese (medical and social). But Ruhm proposes that the reason why obese people doesn't do so is because there are also biological considerations. In particular, he says that "eating behaviors reflect the combined influences of a utility-maximizing deliberative system [the economic part] and an affective system that responds quickly and often impulsively to external stimuli, without accounting for the long-term consequences [the biological part]." Excessive eating results when the "affective system" dominates the deliberative system. Now what is beautiful about this paper is that, like others, it tries to incorporate other scientific fields to explain why man may not be rational (one of economists' century-old mantra). And in this case, it actually makes sense. Now obese people do have some scientific basis for saying in front of a large entree of food: "I can't help it."