There is a new study out saying that people who are slightly overweight (not obese) live longer than those who are not overweight. It isn't really a surprising finding to me, nor is the reaction to it. In particular it was pretty offensive to hear the [Harvard] doctor on NPR flat out rejecting the study as garbage.
Scientists (as well as MD's) do, in fact, trash other scientists' work and findings. Usually this happens when one scientist publishes something that directly refutes an other's work and findings. This initial reaction is not meaningfully different than the way politicians react to the other side, and it is damaging to research overall...particularly in a time when an overlarge number of people are already inappropriately skeptical about science.
The proper response (and the one that the doctor on NPR should have taken) was to say something like: "The study offers some interesting data, and it would be good to go further to look at possible specific cause and effects."
Having more or less body fat isn't really a "cause" of much of anything. It highly correlates with quite a few medical issues (heart health, diabetes, ...), but it is this correlation that is the reason it is used as an indicator, and that is fine. Just because correlation doesn't equal causation doesn't mean we should ignore correlation as indicators.
By the same token, with respect to this study, if people who live longer are more likely to be a little overweight than not, then that could be an indicator that either something has changed in the environment, that something is up with our society, or that the measure of overweight is not as good as it should be. That should be taken seriously, and obviously the Harvard doc doesn't take it seriously.