Being overweight won't kill you - it may even help you live longer. That's the latest from a study that analyzed data on 11,326 Canadian adults, ages 25 and older, who were followed over a 12-year period.

The report, published online last week in the journal Obesity, found that overall, people who were overweight but not obese - defined as a body mass index of 25 to 29.9 - were actually less likely to die than people of normal weight, defined as a B.M.I. of 18.5 to 24.9.

By contrast, people who were underweight, with a B.M.I. under 18.5, were more likely to die than those of average weight. Their risk of dying was 73 percent higher than that of normal weight people, while the risk of dying for those who were overweight was 17 percent lower than for people of normal weight.

The finding adds to a simmering scientific controversy over the optimal weight for adults. In 2007, scientists at the Centers for Disease Control and Prevention and the National Cancer Institute reported that overweight adults were less likely than normal weight adults to die from a variety of diseases, including infections and lung disease.

"Overweight may not be the problem we thought it was," said Dr. David H. Feeny, a senior investigator at Kaiser Permanente Center for Health Research in Portland, Ore., and one of the authors of the study. "Overweight was protective."

He said the finding may be due to the fact that a little excess weight is protective for the elderly, who are at greatest risk for dying, or because many health conditions associated with being overweight, like high blood pressure, are being treated with medication.

The study took into account smoking status, physical activity, age, gender and alcohol consumption. It included a separate analysis excluding those who died early in the 12-year period, in order to weed out participants who might have been thin because they were smokers or had an underlying disease, like cancer.

体重偏重不一定会杀了你--这也许会能让你活的更长。这是来自一项最新的、跟踪研究了11326加拿大人12年的调查所指出的，这些人年龄为25岁或者以上的成年人。

报告上周发布在《肥胖》杂志的网站上，报告指出，总的来说偏重但是不是肥胖的人群--定义为身体雷竞技百科 指数（BMI）*在25到29.9之间--实际上相比正常体重人群（BMI在18.5到24.9之间）死亡的可能会更小。

相比而言，偏瘦的人群（BMI在18.5一下）比正常体重的人有更高的死亡率。死亡率较正常人群高73%;然而体重偏重人死亡率比体重正常人群低17%.

这项发现激发了更多关于成人最适体重的科学争论。2007年，科学家们在美国疾病防控中心和国家癌症研究所的报告里指出偏重的成年人在多种疾病中较正常体重的人有死亡率低，包括传染病和肺炎。

"偏重并不是我们想像的那样。"David H.Feeny博士说，俄勒冈州波特兰Kaiser Permanente健康研究中心的一位高级研究员，并是《偏重保护健康》的作者之一。

他说这些发现可能是因为略微偏重对于面临更高死亡率的老年人比较有保护性，或许因为很多偏重引起的健康状况都可以被治疗，比如高血压。

这项研究考虑了吸烟情况、运动、年龄、性别和饮酒量。研究包括一个单独的分析，排除了那些在这12年调查中很早就死亡的人，主要为了剔除由于吸烟或者患有潜在疾病（比如癌症）所导致体重偏瘦弱的参与者。