A few years ago, Mercedes Carnethon, a diabetes researcher at the Feinberg School of Medicine at Northwestern University, found herself pondering a conundrum. Obesity is the primary risk factor for Type 2 diabetes, yet sizable numbers of normal-weight people also develop the disease. Why?
几年前，美国西北大学(Northwestern University)芬堡医学院(Feinberg School of Medicine)的研究人员梅赛德丝·卡尼索恩(Mercedes Carnethon)遇到了一个难解之谜：肥胖是II型糖尿病最主要的风险因素，然而相当数量体重正常的人也罹患这种疾病。这是为什么?
In research conducted to answer that question, Dr. Carnethon discovered something even more puzzling: Diabetes patients of normal weight are twice as likely to die as those who are overweight or obese. That finding makes diabetes the latest example of a medical phenomenon that mystifies scientists. They call it the obesity paradox.
In study after study, overweight and moderately obese patients with certain chronic diseases often live longer and fare better than normal-weight patients with the same ailments. The accumulation of evidence is inspiring some experts to re-examine long-held assumptions about the association between body fat and disease.
Dr. Carl Lavie, medical director of cardiac rehabilitation and prevention at the John Ochsner Heart and Vascular Institute in New Orleans, was one of the first researchers to document the obesity paradox, among patients with heart failure in 2002. He spent more than a year trying to get a journal to publish his findings.
新奥尔良约翰·奥克斯纳心血管研究所(John Ochsner Heart and Vascular Institute)负责心血管康复和预防的医务主任卡尔·拉维(Carl Lavie)博士是第一批记录肥胖悖论的研究人员之一，2002年，他在心脏衰竭的病人中发现了这一现象。拉维花费了一年多的时间来说服一份期刊发表自己的研究结果。
“People thought there was something wrong with the data,” he recalled. “They said, ‘If obesity is bad for heart disease, how could this possibly be true?’ ”
But there were hints everywhere. One study found that heavier dialysis patients had a lower chance of dying than those whose were of normal weight or underweight. Overweight patients with coronary disease fared better than those who were thinner in another study; mild to severe obesity posed no additional mortality risks.
In 2007, a study of 11,000 Canadians over more than a decade found that those who were overweight had the lowest chance of dying from any cause.
To date, scientists have documented these findings in patients with heart failure, heart disease, stroke, kidney disease, high blood pressure — and now diabetes.
Experts are searching for explanations. One idea is that once a chronic disease develops, the body becomes catabolic, meaning it needs higher energy and caloric reserves than usual. If patients do not have those reserves, they may become malnourished even though their weight is normal, said Dr. Gregg Fonarow, one of the directors of the preventive cardiology program at the University of California, Los Angeles.
专家们在寻求答案。一种观点是，一旦人体出现了慢性疾病，新陈代谢随之加快，意味着需要比往常更多的能量和热量储备。加州大学洛杉矶分校(University of California, Los Angeles)心脏病预防项目主任之一格雷格·佛纳罗(Gregg Fonarow)博士介绍说，如果患者没有这些储备，即使体重正常，也可能营养不良。
Some researchers suspect genetics: Maybe thin people who develop diabetes, cardiovascular disease and other chronic ailments have gene variants that make them more susceptible to these illnesses and put them at greater risk once they become ill. Heart disease in thin people may represent a different illness from heart disease in heavier people, Dr. Lavie said.
It may be that doctors do not treat thin patients as aggressively as they do heavier patients — or that the yardstick itself is to blame. Most researchers assess obesity by measuring body mass index, a simple ratio of height and weight. But B.M.I. does not take into account body fat, lean muscle mass, metabolic abnormalities and other nuances of physical composition.
Perhaps, some experts say, we are not asking the right question in the first place. Maybe we are so used to framing health issues in terms of obesity that we are overlooking other potential causes of disease.
Dr. Neil Ruderman, an endocrinologist at Boston University School of Medicine, was the first to identify a condition he called “metabolically obese normal weight,” in 1981. Such people have weights in the normal range on the B.M.I. chart but also have metabolic abnormalities, including high levels of insulin resistance and triglycerides; they tend to carry fat around the middle, which is more apt to affect the heart, liver and other organs than fat in the hips and thighs.
尼尔·鲁德尔曼(Neil Ruderman)博士是波士顿大学医学院(Boston University School of Medicine)的内分泌学专家，1981年他第一次明确了一种现象，他称之为“正常体重代谢性肥胖”(metabolically obese normal weight)。表现出这种症状的病人在BMI图表上的体重处在正常值范围内，但却存在着新陈代谢异常，包括高胰岛素抗性和高甘油三酯；他们腰间往往像套了个救生圈，相比那些脂肪囤积在臀部和大腿的人来说，这种情况更容易影响心脏、肝脏还有其他器官。
“If we’re open-minded when we look at the data, we often find confounding factors that can explain the disease associations we blame on weight,” said Linda Bacon, a nutrition professor at City College of San Francisco and author of “Health at Every Size: The Surprising Truth About Your Weight.”
“如果在研究这些数据时候心态更加开放，往往会发现那些被我们归咎于体重的疾病，是有着其他易于混淆的因素可以解释的，”旧金山市立学院(City College of San Francisco)营养学教授琳达·培根(Linda Bacon)说。她也是《各种体型的健康：关于体重的惊人真相》(Health at Every Size: The Surprising Truth About Your Weight)一书的作者。
Fitness is an important, and often unmeasured, confounder, and the growing pile of paradoxical evidence is forcing experts to re-evaluate its importance.
The link between obesity and health derives in part from research like the Framingham Heart Study, which has followed thousands of men and women since the 1940s. But Paul McAuley, a professor of health education at Winston-Salem State University, has noted that Framingham and other longitudinal studies often fail to take into account physical activity and fitness.
肥胖和健康之间的联系，部分源自像弗莱明汉心脏研究所(Framingham Heart Study)这种机构提供的研究报告，该研究所从20世纪40年代开始跟踪调查数以千计的男性和女性。但是，温斯顿—塞伦州立大学(Winston-Salem State University)健康教育学教授保罗·麦考利(Paul McAuley)指出，弗莱明汉的相关研究和其他纵贯性研究(longitudinal studies)，往往没有将人们的体力活动和体质考虑进去。
Research that does tease apart weight and fitness — like a series of studies conducted by Steven Blair at the Cooper Institute in Dallas — shows that being fat and fit is better, healthwise, than being thin and unfit. Regular aerobic exercise may not lead to weight loss, but it does reduce fat in the liver, where it may do the most metabolic damage, according to a recent study at the University of Sydney.
有些研究确实把体重和体质区分开来——达拉斯库珀研究院(Cooper Institute)的史蒂夫·布莱尔(Steven Blair)所做的系列研究正是其中之一——他的研究表明，从健康角度来说，身材胖但体质好，比身材瘦但羸弱要更好。悉尼大学(University of Sydney)最近的一项研究表明，定期的有氧运动可能不会让体重变轻，但是确实能够减少肝脏里的脂肪，那是最有可能发生代谢异常的器官。
“More often than not, cardiovascular fitness is a far more important predictor of mortality risk than just knowing what you weigh,” said Glenn Gaesser, author of “Big Fat Lies” and director of the Healthy Lifestyles Research Center at Arizona State University.
“多数情况下，保持心血管健康远比仅仅知道自己的体重更能预测死亡风险，”《大谎言》(Big Fat Lies)作者、亚利桑那州立大学(Arizona State University)健康生活研究中心(Healthy Lifestyles Research Center)主任格伦·加瑟尔(Glenn Gaesser)说。
In 2005, an epidemiologist, Katherine Flegal, analyzed data from the National Health and Nutrition Examination Survey and found that the biggest risks of death were associated with being at either end of the spectrum — underweight or severely obese. The lowest mortality risks were among those in the overweight category (B.M.I.s of 25 to 30), while moderate obesity (30 to 35) offered no more risk than being in the normal-weight category.
2005年，流行病学家凯瑟琳·弗莱戈(Katherine Flegal)分析了美国国家健康与营养调查(National Health and Nutrition Examination Survey)的数据，发现死亡风险最大的人群是那些位于体重两端的人们——体重过轻或者严重肥胖。死亡风险最低的人群是超重人士（BMI值在25-30之间），而中度肥胖者（30-35）和正常体重范围的人死亡风险一样高。
Whatever the explanation for the obesity paradox turns out to be, most experts agree that the data cast an uncertain light on the role of body fat. “Maintaining fitness is good and maintaining low weight is good,” Dr. Lavie said. “But if you had to go off one, it looks like it’s more important to maintain your fitness than your leanness. Fitness looks a little bit more protective.”
That is a message that may take a long time to reach your family physician, however. “Paradigm shifts take time,” Ms. Bacon said. “They also take courage. Not many people are willing to challenge the weight conventions. They’re just too culturally embedded, and the risk of going against convention is too high.”
然而，这个信息可能需要很长时间才能被你的家庭医生接受。“范式的转变需要时间， 也需要勇气。不是很多人愿意质疑关于体重的传统看法。这一看法在文化上太根深蒂固，而挑战传统又是冒天下之大不韪。” 培根说。