Weight vs. death

http://www.eurekalert.org/pub_releases/2007-11/jaaj-sea110107.php

Study examines association between weight amount and cause of death
The association between weight and causes of death can vary considerably, with obesity associated with a significantly increased mortality from cardiovascular disease (CVD), underweight associated with increased mortality from primarily non-cancer, non-CVD causes, and overweight associated with increased mortality from diabetes and kidney disease combined, but with reduced mortality from other non-cancer non-CVD causes of death, according to a study in the November 7 issue of JAMA.
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“Some evidence suggests that modestly higher weights may improve survival in a number of circumstances, which may partly explain our findings regarding overweight. Overweight is not strongly associated with increased cancer or CVD risk, but may be associated with improved survival during recovery from adverse conditions, such as infections or medical procedures, and with improved prognosis for some diseases. Such findings may be due to greater nutritional reserves or higher lean body mass associated with overweight,” the authors write.

Extra weight may very well be helpful in some diseases for the stated reasons. But another aspect which has been commented on in previous similar studies, is that an undiagnosed disease, such as cancer, may cause weight loss. So we cannot tell from the statistics how much, if any, protection there may be from extra weight. I guess researchers don't have time to read the results of other studies.