What do you know about BMI and lifespan？

BMI: body mass index

BMI是体重指数。

Wikipedia: “BMIs under 20 and over 25 have been associated with higher all-cause mortality, with the risk increasing with distance from the 20–25 range.[2]”

维基百科：“20 以下和 25 以上的 BMI 与更高的全因死亡率相关，风险随着距离 20–25 范围的距离增加而增加。”

我一直以为这是“真理”。但是，昨天的一篇文章，让我“大掉眼镜”。【没有耐心的人，这里是答案：BMI在25–30之间（胖，但不是巨胖），寿命比“正常BMI（20–25）的人”要长。所以，如果你发现减肥好辛苦，可以躺平了。】

我复制了文章的“有关内容”：

She saw the obesity epidemic coming. Then an unexpected finding mired her in controversy.

她看出肥胖（流行）病的到来。然后一个意想不到的科研发现使她陷入了争议。

Katherine Flegal was a scientist who found herself crunching numbers for the government, until one day her analyses set off a firestorm. What does she make of her decades as a woman in public health research?

Katherine Flegal 是一位为政府处理大数据的科学家，直到有一天她的分析结果引发了一场风暴。作为一名从事公共卫生研究的女性，她如何看待自己的几十年生涯？

By Alice Callahan 09.08.2022

https://knowablemagazine.org/article/society/2022/obesity-research-controversy-woman-scientist?utm_source=email&utm_medium=knowable-newsletter&utm_campaign=K_newsletter_2022-09-11

Katherine Flegal wanted to be an archaeologist. But it was the 1960s, and Flegal, an anthropology major at the University of California, Berkeley, couldn’t see a clear path to this profession at a time when nearly all the summer archaeology field schools admitted only men. “The accepted wisdom among female archaeology students was that there was just one sure way for a woman to become an archaeologist: marry one,” Flegal wrote in a career retrospective published in the 2022 Annual Review of Nutrition.

Katherine Flegal 想成为一名考古学家。但那是 1960 年代，在加州大学伯克利分校就读人类学专业的 Flegal发现几乎所有夏季考古野外学校都只招收男性，她看不到这个职业的前途。 “女性考古学学生普遍接受的认知是：女性成为考古学家只有一种方式，就是嫁给一个考古学家，” Flegal在 2022 年营养年度评论发表的职业回顾中写道。（译者注：可见“出身年代”有多重要！）

Can you tell us more about what NHANES is, and why it’s important?

NHANES is an examination survey, so there are mobile units that go around the country and collect very detailed information from people; it’s like a four-hour examination. When you read about things like the average blood cholesterol in the United States, that kind of information almost always comes from NHANES, because it’s a carefully planned, nationally representative study of the US population. It started in the early 1960s, and it’s still running today. （译者注：这是介绍NHANES“普查”如何获取老百姓的健康资料。）

One of the things that distinguishes NHANES from other data sources is that it directly measures things like height and weight, rather than just asking people about their body size. Why does that matter?

People don’t necessarily report their weight and height correctly for a variety of reasons, not all of which are fully understood. There’s a tendency to overestimate height; there’s kind of a social desirability aspect probably involved in this. And there’s a tendency for people, especially women, to underreport their weight a little bit. Maybe they’re thinking “I’m going to lose five pounds,” or “This is my aspirational weight,” or they don’t really know, because they don’t weigh themselves.

That can make a difference — not huge, but enough to make quite a difference in some studies. And what you don’t know is whether the factors that are causing the misreporting are the same factors that are affecting the outcome. That’s very important and overlooked. It’s a risky business to just use self-reported data. （译者注：NHANES“普查”通过走访获得老百姓的健康资料。而不是让老百姓自报身高体重。这样，数据误差小一点。）

Did you face pushback from within the CDC for some of the things that you were publishing?

Yes. This really started in 2005, when we wrote an article estimating deaths associated with obesity. The CDC itself had just published a similar article the year before with the CDC director as an author, which is fairly unusual. That paper said that obesity was associated with almost 500,000 deaths in the US and was poised to overtake smoking as a major cause of death, so it got a lot of attention.

In our paper, we used better statistical methods and better data, because we had nationally representative data from the NHANES, and my two coauthors from the National Cancer Institute were really high-level statisticians. We found that the numbers of deaths related to obesity — that’s a BMI of 30 or above — were nothing as high as they found. But we also found that the overweight BMI category, which is a BMI of 25 up to 29.9, was associated with lower mortality, not higher mortality.

在我们的论文中，我们使用了更好的统计方法和更好的数据，因为我们有来自 NHANES “普查”的具有全美国代表性的数据，而我的来自国家癌症研究所的两位合著者都是真正的高级统计学家。我们发现与肥胖相关的死亡人数——即 BMI 为 30 或以上——并没有他们（指CDC）发现的那么高。但我们还发现，超重 BMI 组的人，即 25 –29.9 的 BMI的人，与较低的死亡率相关，而不是与较高的死亡率相关。

We had this wildly different estimate from what CDC itself had put out the year before, so this was an awkward situation for the agency. The CDC was forced by the press to make a decision about this, and they kind of had to choose our estimates, because they couldn’t defend the previous estimates or find anything wrong with ours. The CDC started using them, but they were tucked away. It was really played down.

That study generated a lot of media attention and criticism from other researchers. Was that a surprise to you?

该研究引起了媒体关注和其他研究人员的大量批评。这让你感到意外吗？

Yes, that was completely a surprise. There was so much media attention immediately. I had to have a separate phone line just for calls from journalists. And almost immediately, the Harvard School of Public Health had a symposium about our work, and they invited me, but they didn’t offer to pay my way. CDC said that they didn’t want me to go, so that was the end of that. But the final lineup they had was other people saying how our findings didn’t agree with theirs, so this whole symposium was basically an attack on our work.

是的，这非常让我吃惊。我们的研究立刻引起了媒体的广泛关注。我必须有一条单独的电话线来接听记者的电话。几乎在同时，哈佛公共卫生学院就我们的工作召开了一次座谈会。他们邀请了我，但他们没有提出付我的旅差费用。CDC不想让我去，所以就没有去。但他们最后的阵容是其他人说我们的研究结果与他们的不一致，所以整个研讨会基本上是对我们工作的攻击。

You and coauthors also published a meta-analysis of 97 studies in 2013 that found that being overweight or mildly obese wasn’t associated with a greater risk of mortality. Did you face a similar response to that article?

你和合著者还在 2013 年发表了对 97 项研究的荟萃分析，发现超重或轻度肥胖与更高的死亡风险无关。你对那篇文章有类似的回应吗？

We embarked on a systematic review and found that these results pretty much agreed with what we had already found. We published that, and there was a lot of criticism, another symposium at Harvard, and just a lot of attacks. The chair of Harvard’s nutrition department, Walter Willett, went on NPR and said that our paper was so bad that nobody should ever read it, which is a pretty unusual thing for a scientist to be saying.

我们开始进行系统审查，发现这些结果与我们已经发现的结果非常一致。我们发表了那篇文章，受到了很多批评，在哈佛举行的另一场研讨会，我们还受到很多攻击。哈佛营养系主任Walter Willett继续在 NPR （国家公共广播电台）上说我们的论文太糟糕了，以至于任何人都不应该阅读它，这对于科学家来说是一件非常离奇的事情。

When you look at how much your work has been cited, and how much influence it had, it seems you had quite an impact.

当您查看您的工作被引用了多少次、以及它有多大影响时，您看到您产生了相当大的影响。

I think I did, but it really wasn’t what I expected or set out to do. I got into this controversial area pretty much by accident. It caused all this brouhaha, but I don’t back down.

我想我的确产生了相当大的影响，但这确实不是我期望或打算做的。我进入这个有争议的领域几乎是偶然的。它引起了这些骚动，但我没有退缩。

We were all senior government scientists who had already been promoted to the highest level. In a way, it was kind of lucky that I was working for CDC. Writing those articles, it was a career-ending move. If I had had anything that could have been destroyed, somebody would have destroyed it. I think I wouldn’t have gotten any grants. I would have become disgraced.

我们当时都是政府高级科学家，已经升到最高级职称了。在某种程度上，我在 CDC 工作是一种幸运。写这些文章，会是一个职业生涯的终结。如果我有任何可以被摧毁的东西，那么有人一定会摧毁它。我想我不会得到任何新的资助。我会“臭名昭著”。

But this stuff is serious. It’s not easy, and everybody has to decide for themselves: What are they going to stand up for?

但这件事（体重指数和健康）本身很重要。处理这种事并不容易，每个人都必须自己决定：我要“挺”什么？