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.

    體重偏重不一定會殺了你--這也許會能讓你活的更長。這是來自一項最新的、跟蹤研究了11326加拿大人12年的調查所指出的，這些人年齡為25歲或者以上的成年人。

    報告上周發布在《肥胖》雜志的網站上，報告指出，總的來說偏重但是不是肥胖的人群--定義為身體質量指數（BMI）*在25到29.9之間--實際上相比正常體重人群（BMI在18.5到24.9之間）死亡的可能會更小。

    相比而言，偏瘦的人群（BMI在18.5一下）比正常體重的人有更高的死亡率。死亡率較正常人群高73%;然而體重偏重人死亡率比體重正常人群低17%.

    這項發現激發了更多關于成人最適體重的科學爭論。2007年，科學家們在美國疾病防控中心和國家癌癥研究所的報告里指出偏重的成年人在多種疾病中較正常體重的人有死亡率低，包括傳染病和肺炎。

    "偏重并不是我們想像的那樣。"David H.Feeny博士說，俄勒岡州波特蘭Kaiser Permanente健康研究中心的一位高級研究員，并是《偏重保護健康》的作者之一。

    他說這些發現可能是因為略微偏重對于面臨更高死亡率的老年人比較有保護性，或許因為很多偏重引起的健康狀況都可以被治療，比如高血壓。

    這項研究考慮了吸煙情況、運動、年齡、性別和飲酒量。研究包括一個單獨的分析，排除了那些在這12年調查中很早就死亡的人，主要為了剔除由于吸煙或者患有潛在疾病（比如癌癥）所導致體重偏瘦弱的參與者。