"A body mass index under  is deemed normal and healthy and a higher BMI thats overweight or obese is not. But that might be changing at least when it comes to risk of death. The body mass index or BMI associated with the lowest risk of death has increased since the s a study finds from . in the normal weight category to  which is deemed overweight. That means a person who is foot could weigh  pounds and be in that epidemiological sweet spot according to the NIHs online BMI calculator http_wtBMIbmicalc.htm. The results  httpjama.jamanetwork.comarticle.aspxarticleidwere published Tuesday in JAMA the journal of the American Medical Association. The researchers came to that conclusion by looking at data from three studies of people in Copenhagen one from the s one from the s and one from . More than  people were involved. Because Denmark has an excellent national health registry they were able to pinpoint the cause of death for every single one of those people. The risk of death for people who are obese with a BMI of  or greater also declined to the point that it was on a par with some people of socalled normal weight. So being fatter at least a bit may be healthier. I was surprised as a scientist to see how clear the result was Borge Nordestgaard a clinical professor and chief physician at Copenhagen University Hospital and senior author of the study told Shots. So he and his colleagues sliced and diced the data to see what could account for the shift. They looked at age sex smoking cancer and heart disease. The most relevant was the decline in smoking since the s. But when they looked at the mortality rates in nonsmokers who had never had cancer or heart disease it also became associated with a higher BMI over time. Article continues after this message from our sponsor So whats going on Now we get into the speculation part right I know you journalists always want that Nordestgaard says. One option certainly is over these three decades we have become much better at treating the cardiovascular risk factors that come with overweight and obesity. That includes treating high cholesterol with statins treating high blood pressure with diet exercise and an array of medications and making concerted efforts to help people to control blood sugar. People in Denmark got heavier on average over the course of the study as they have in the United States and most other countries. By   percent of the Danes had a BMI of  or higher. So you could think OK the new average is a heavier average. Or you could wonder if being a bit heavier somehow helps confer health benefits that affect longevity. Researchers have long known that people who are very thin tend to have a shorter life expectancy often because theyre dealing with cancer or other serious illnesses. The sweet spot on the BMIlongevity axis is typically somewhere near the middle. But theres not much data to back the notion that a bit more pudge is protective. This is total speculation Nordestgaard says. The BMI has been vilified  http a poor measure of an individuals health. Someone who is big fit and wellmuscled like a pro football player http can peg an obese BMI. And all of the people in this study are white so thats a limitation. But the BMI which is a general measure of body fat has proven useful for thinking about the health of large groups of people as in this study. Nordestgaard and his colleagues are going to dig into this more in an effort to figure out whats going on but he cautions that these kinds of data dives can take many months. But this does raise the prospect of whether it may soon be time to tweak the official definition of normal healthy weight."