A study on the health risks of being overweight has been in the news of late, as it declares the effect on mortality rates of modest excess weight to be much lower than previously estimated. This sort of news is always received well for all the obvious (and poor) reasons - people like to be told that they aren't doing so badly after all.
Unfortunately, we simply can't take each new study as the last word on any complex topic in science; statistics and human health are certainly both complex topics. The process of scientific investigation, research and debate on any given subject produces an array of papers supporting each major position as the years go by. Only slowly does the preponderance of evidence lean one way or another, and certain answers must wait for a complete understanding of the underlying processes and factors involved.
I have opined before on the merits of being a conservative late adopter in matters relating to healthy and healthy life extension; the points are still valid. A wait and see attitude is a good thing in my book:
Science is a debate aimed at discovering the truth, supported by tested methodologies for determining, reviewing, interpreting and predicting facts. Important questions, especially those related to medicine and statistics, are not answered with a single study. Each study, and the resulting debate, can take years. Building - or changing - even a preliminary scientific consensus on any position is a process that spans decades.
People are hungry for definitive answers. Nobody likes an unanswered or partially answered question, but unanswered questions are the essence of science. All "answers" provided by science are theories, possibly wrong in as-yet undetermined ways, and subject to replacement when a better theory emerges.
So while looking at this latest study on one hand and a plate of donuts on the other, bear in mind that there are still a great many studies out there to demonstrate that even modest excess weight greatly increases the chance of suffering common age-related diseases. A last word from the article linked above:
Dr. JoAnn Manson, chief of preventive medicine at Brigham and Women's Hospital in Boston, said she is not convinced that the new estimate is right: "It's likely there has been a weakening of the mortality effect due to improved treatments for obesity. But I think this magnitude is surprising and requires corroboration."
Improved treatments or not, it's probably not a good idea to expect medical science to rescue you from the future costs - financial and otherwise - of failing to take care of your health now.