体重正常也会可能是肥胖

Can you be normal weight and fat at the same time?

That's the implication of a provocative recent report from the Mayo Clinic, which suggests that fat in your body can get you and your heart into trouble even if you don't look fat and if the scale tells you you're healthy.

The Mayo researchers, led by cardiologist Francisco Lopez-Jimenez, have coined a term for the phenomenon: normal weight obesity. In a study that looked at data from 6,171 Americans with normal body size, as measured by body mass index, those with a high percentage of body fat were at significantly greater risk of future heart problems than those with low amounts of fat. Their bodies 'behave like they are obese, but they are not,' Dr. Lopez-Jimenez says.

People don't have to be overweight to have excess body fat. Instead, these people have a higher ratio of fat to muscle tissue than do people with low body fat. Indeed, even people of the same weight, or those with comparable body mass index, which factors together weight and height, can have different body-fat percentages.

Based on results of the nine-year study, as well as U.S. Census and obesity data, Dr. Lopez-Jimenez and his colleagues estimate that as many as 30 million Americans may fall into the normal-weight-obesity category, many of them unaware they may be at increased heart risk.

The study 'drills down on a population where we're making assumptions that everybody is healthy. It may well be that they're not,' says Robert Eckel, an obesity and metabolic-syndrome expert at the University of Colorado, Denver, who wasn't involved with the study.

But Dr. Eckel and other medical experts caution that the findings need to be validated with additional research. Big epidemiological studies such as the Mayo report are useful for spotting important trends and raising hypotheses for further inquiry. But they are not necessarily reliable for prescribing specific remedies for individual patients.

Indeed, Dr. Eckel says he doesn't think the study's results mean people should have their body fat measured to assess their cardiac risk. Generally, a little extra weight around the middle among normal weight people should be a sufficient wakeup call, other doctors say. More research is needed to determine whether reducing body fat percentage in such people would lower risk of heart disease.

Among some of the Mayo Clinic study's findings: High body fat among normal-weight men and women was associated with a nearly four-fold increase in the risk for metabolic syndrome -- a cluster of abnormalities including elevated blood sugar and blood pressure. This syndrome is common among people who are obese and is an increasingly important precursor to diabetes and cardiovascular disease. For women, high body fat meant a heightened risk of being diagnosed with cardiovascular disease over the course of the study. Both men and women had a higher risk of abnormal cholesterol and men with high body fat were more likely to develop high blood pressure.

The research suggests that body mass index, or BMI, the tool doctors and researchers often use to determine whether a person is obese, may fall short in some cases as an indicator of good health. BMI is obtained by dividing your weight in kilograms by your height in meters squared. People with a BMI between 18.5 and 24.9 -- the range for the participants in the Mayo study -- are considered to be normal weight under government guidelines. A BMI of 30 or higher indicates obesity, while people in the range from 25 to 29.9 are considered overweight. The overweight category in particular has generated controversy because many people who exercise regularly and are considered fit have BMIs above 25.

这就是美国梅奥医院（the Mayo Clinic）最近发布的一份引人注意的报告中所提出的问题，即人体内的脂肪能给人和其心脏造成麻烦，即使一个人看上去不胖，而体重秤也说其体重在健康范围内。

由心脏病专家希门尼斯（Francisco Lopez-Jimenez）领导的梅奥的研究人员们为这种现象发明了一个新词：体重正常的肥胖症。他们做了一项研究，调研了6,171 名按身体质量指数（BMI）来说属于体形正常的美国人，发现那些体内脂肪含量高的人，其将来患心脏病的风险大大超过了那些体内脂肪含量低的人。他们的身体的“运作方式如同患肥胖症的人们，但他们却并不肥胖，”希门尼斯说。

体内脂肪过多的人的体重不一定超重。相反，相比身体脂肪量低的人，这些人的体内脂肪与肌肉组织的比值比较高。事实上，体重或身体质量指数（此指数综合考虑了人的体重和身高）相同的人，其体内脂肪含量的百分比也会有所不同。

根据这项历经九年的研究结果，加上美国政府的人口统计和肥胖症数据，希门尼斯和他的同事估计，多达30万的美国人可能患上了体重正常的肥胖症，其中许多人还不知道他们患心脏病的风险可能会增加。

这项研究“深度研究了那部分我们以为都是健康的人群，而他们很可能并不健康”，研究肥胖症和代谢综合症的美国科罗拉多州丹佛大学的专家埃克尔（Robert Eckel）说。他没有参与该项研究。

但是，埃克尔和其他医学专家提醒说，这些发现还有待进一步的研究加以验证。象梅奥报告这样大型的流行病学研究，在认清重大趋势和为进一步调研提出假设方面是很有用的；但在为个体的病人提出具体治疗方案方面，这些研究结果不一定可靠。

埃克尔说， 事实上，他不认为研究结果意味着人们应该通过测量身体脂肪含量来评估他们患心脏病的风险。其他医生说，一般来说，当正常体重的人腰部长出一圈脂肪就该引起足够的警觉。若要证明此类人如果体内脂肪比例降低其患心脏病的风险是否也会随着降低，还需要做更多的研究。

梅奥诊所的研究结果还包括：体内脂肪高但体重正常的男性和女性，其患代谢综合症的风险增加了近4倍。代谢综合症是包括高血糖和高血压在内的一系列异常现象的组合。这种综合症在肥胖人群中属常见，也越来越成为糖尿病和心血管疾病的一个重要先兆。在研究过程中，高脂肪的妇女显示被诊断患心血管疾病的风险更高。胆固醇含量异常的风险无论男女都要更高，而高脂肪男子患高血压的几率则更高。

研究表明，尽管BMI是医生和研究人员经常借助用以确定一个人是否患有肥胖症的一个工具，但在某些情况下，它还不能具备判断一个人是否健康的功能。BMI是由一个人的体重（以公斤为单位）除以其身高的平方（以米为单位）。按政府公布的参考指标，BMI介于18.5至24.9之间的人，其体重被视为正常，这些人也是梅奥研究的取样对象。BMI为30或更高的则为肥胖，而介于25至29.9之间则被认为超重。对超重类的划分尤其有争议，因为许多经常运动而被认为健康的人的BMI超过了25。