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You can also listen to this episode on Spotify!The new weight loss drugs such as Ozempic are stunningly effective at helping patients lose weight and improve their metabolic health. Their existence also seems to have intensified polarizing rhetoric around weight, health and BMI. On one end of the ideological spectrum, there is the “Healthy at Every Size” (HAES) movement that aims to decouple weight from worthiness—and argues that doctors who recommend weight loss to their patients with obesity do more harm by enabling body shaming without evidence to support the benefits of weight loss on health. On the other end of the spectrum is the camp that believes obesity is a result of poor health and life choices—and that patients with obesity should simply eat better and exercise more rather than succumb to the pharmaceutical industry’s latest fad. Emily Osteris a Professor at Brown University, a best-selling author, and a leading voice in health economics. In her wildly popular newsletter, ParentData , she tackles pressing health issues of the day, helping people frame risk in order to make everyday decisions. Dr. Oster joins Dr. McBride on this week’s episode of Beyond the Prescription to discuss the data on BMI and health, and how to empower readers and listeners with nuanced information to be healthy, inside and out. They review the data on the health benefits of exercise, independent of weight loss; the arbitrariness of BMI cut-offs; and the importance of focusing on health habits over a specific target weight. They agree that doctors do harm when they narrowly define health as a number on a scale—and the metabolic health involves addressing the medical, nutritional, behavioral or social-emotional elements of people’s health. As Dr. McBride says, “Sometimes that includes weight loss medication. Sometimes it’s a prescription to stop dieting and start eating lunch.”The transcript of our conversation is here![00:00:00] Dr. Lucy McBride: Hello, and welcome to my office. I'm Dr. Lucy McBride, and this is Beyond the Prescription, the show where I talk with my guests like I do my patients, pulling the curtain back on what it means to be healthy, redefining health as more than the absence of disease. As a primary care doctor, I've realized that patients are more than their cholesterol and their weight.[00:00:31] We are the integrated sum of complex parts. Our stories live in our bodies. I'm here to help people tell their story and for you to imagine and potentially get healthier from the inside out. You can subscribe to my free weekly newsletter at lucymcbride.substack.com and to the show on Apple Podcasts, Spotify, or wherever you get your podcasts.[00:00:57] So let's get into it and go Beyond the Prescription. Today we have an amazing guest joining us, my friend Dr. Emily Oster. Emily is a renowned economist, a bestselling author, and a professor at Brown University. Emily is one of the leading voices in health economics. Her superpower is applying data to some of society's thorniest health questions, including why people don't always make rational health decisions.[00:01:30] In her wildly popular newsletter called Parent Data, Emily tackles pressing issues about pregnancy and parenting, helping decisions. I grabbed Emily today because I wanted to talk with her about her recent piece on body weight and health: What is the relationship between BMI and health? She pulled together a lot of data, and because weight is something I talk about with my patients every day, I thought I'd grab her for a chat. Emily, thank you so much for joining me today.[00:02:03] Emily Oster: Thank you so much for having me. It is a delight as always to see you. It's such a treat.[00:02:09] LM: Emily, you are no stranger to controversy. In fact, I was with you in the proverbial bunker during COVID, hiding from the haters who didn't like that you and I were trying to help message about risk. We were trying to help people better calibrate their degree of anxiety around COVID to their level of actual risk.[00:02:31] By the way, I stand by everything I said and wrote. I hope you do too. And it was so fun to work with you then as it is now. So when I think about sensitive subjects, I think also about weight. And so, why did you want to write about weight? Is it just that you like putting your finger in the electrical socket? Or, did you have something to say?[00:02:49] EO: So I've actually written about weight a bunch of times. So it is a topic that I work on in my academic work. So as a professor in economics, the work that I do is about health economics and statistical methods. And I actually work a lot on diet and dietary choices and why people make the dietary choices they do.[00:03:07] And so it's not specifically about weight, but it really is about food. And so this is a kind of source of data that I think about a lot. And as a result, I've written about a lot in many different ways. And every time I come at this and I've come at it from all of the angles. So I wrote a piece once called what's the best diet? [00:03:31] And it was just like the diet that you can stick to which is a sort of standard finding. But the frame was, you know, a lot of people are interested in diet. And when I write that, many people are very angry. They're sort of like, no diet works, we should never talk about dieting, is kind of what comes back.[00:03:48] I did an interview with Virginia Sol Smith, who I really like, and we don't always agree but is just one of my favorite people to talk to. She always makes me think about her book Fat Talk, which is very much in the other direction, sort of very much in the space of, we should definitely not be talking about BMI, we should throw away our scales, all foods are neutral.[00:04:10] And when I published that interview, I got it from the other side. I got the, you know, how could you possibly say this, cake and apple are not the same, like this is, this is insane. And I've written about Ozempic, so just anything, I mean, you know this—anytime you write about it in this space, there's really, really strong feelings from both sides.[00:04:26] So this piece was trying, as I always do, more or less, sometimes more successfully than others, is to try to thread the needle and say, look, let’s look at the data and see between the view of BMI is completely meaningless and correlated with nothing, and the view that your BMI is completely deterministic of your health and that is the only information we should use.[00:04:49] Where is the truth? And how can we use the data to get to that?[00:04:52] LM: It is such a crucial question because everybody who's paying attention reads the headlines and understands from their doctor even that weight and weight management is good for your health. We have diet culture seeping into our pores. I mean, it's sort of in the air we breathe, everything you look at on the covers of magazines, on Instagram, and in doctor's offices is about weight, or it feels like it's about weight.[00:05:20] I see people all the time who have avoided coming to see me, even if I've known them for decades, because they thought they would feel better about themselves, and I would feel more proud of them if they had just lost weight before they came in. And as I say to patients all the time, weight is one piece of a larger puzzle.[00:05:36] It is not a reflection of your value, your worth. And it certainly doesn't tell us everything about your health. So I'd love to hear about your findings about the relationship between BMI and actual health. [00:05:50] EO: In my mind, the most, the sort of most important thing to note here is that something can be correlated and can have some explanatory power and not be all of the explanatory power. So one version of this question is to say, on average, if your weight is higher, are you more likely to have other health conditions?[00:06:13] And I should say, that's actually different from the question of whether weight causes other health conditions. But purely taking this from like a correlational standpoint, if you saw one piece of data about someone, you saw their BMI, would you learn anything about their health? And the answer is, yes. On average, there is a relationship, particularly at the upper end of BMI, between increasing BMI and worse health.[00:06:41] And in particular, worse metabolic health. So things like, there's a strong correlation between high weight and diabetes. That's just true in the data. Now, those relationships... are there, but they're actually not as big, I think, as many people think. And that's sort of the other thing that comes out of this.[00:06:58] And that, that has two parts. So one is actually, even to the extent that there's a positive relationship there, it doesn't show up until you start getting to sort of higher levels of BMI. So sometimes we talk, we talk about overweight being 25 BMI versus 24. Actually, the health differences between people with a BMI in the 25 to 30 versus 20 to 25, if anything, probably favor the 25 to 30, but you're certainly not seeing much in that range.[00:07:30] As you get into a BMI of 35-40 you do see some of those, some of those correlations. But it's also true that in almost any health outcome you look at there is variation within a group and that's the thing I was sort of trying to illustrate in the piece is you look at something like diabetes or the distribution of blood pressure, like the distribution of blood pressure, it's shifted up for people who are higher BMI, but there's a lot of overlaps.[00:07:56] Plenty of people with high blood pressure whose BMI is 19 and plenty of people with low blood pressure whose BMI is 38. And so that's the sense in which like this number Tells you maybe a little bit, but really not that much.[00:08:12] LM: let's talk about what BMI is. BMI, I mean, you define it for us here, Emily.[00:08:17] EO: BMI is a weight in kilograms divided by your height in meters squared. It's just a number.[00:08:22] LM: So what you pointed out so beautifully in your piece is that medicine does this weird thing where we say that a normal BMI, body mass index, is between 20 and 24.9, and overweight is 25-29. 9 [00:08:37] EO: You guys love a sharp cutoff. It's your, it's your favorite. You love it.[00:08:42] LM: I don't, but fine. The medical establishment loves these arbitrary cutoffs. There's nothing magical or particularly different between somebody who has a BMI of 24.9 and 25 and moreover, there are so many different elements that go into this whole person's health. That to call it a diagnosis point X and not a diagnosis at X minus .1 is ridiculous. So, you know, herein lies why we're here to talk about pulling back the curtain on what this actually means.[00:09:18] EO: Right. And, and so I should say, like, you might wonder why have any cutoffs in this at all? I think the answer to that is that when people are describing, not even doctors, when population health scientists are describing characteristics of populations, it can sometimes be useful to define categories.[00:09:40] So, you see this in weight, you also see it in something like low birth weight is another good example which has some cut-offs, right? So when we talk about baby weight, there's a number, 2,500 grams. And if a baby is below 2,500 grams, they're classified as low birth weight, and if they're above 2,500 grams, they're not.[00:09:56] There's nothing special about 2,500 grams, obviously, but it’s helpful when we sort of describe a population. You want to say, does this, you know, is the low birth weight share in this population bigger than this population? We want to have a common language. And so saying, like, that's the cutoff we're going to use, so we have some number to compare, is helpful, it can be helpful. The same thing happens here. You want to describe characteristics of a population. I think the problem, and it actually shows up in the birth weight also, but the problem comes when we start, we take that, which is just away to use a number to make some descriptive statements about some population.[00:10:35] When we take that number and we decide it's meaningful. It's like a somehow a meaningful number that we would, that would tell us something if you were on either side of it. Of course it's not. And when you're using it for populations, for individuals and populations on which it was not based, I mean, this is a much deeper issue, but when we talk about BMI in particular, this is something, these are sort of cutoffs that were developed with reference to like a white European population, they may have very different meanings and relationships with health for different populations off of which they are not based. So there's a sort of whole other can of worms there.[00:11:14] LM: Totally. It's, I mean, to make an analogy briefly that you and I are familiar with is, you know, COVID risk, right? It's not that a 65-year-old, every 65 year old is at so much higher risk for outcomes. Then every 64-year-old, but there is truth to the fact that older people tend to get sicker on a population level when I'm talking to a patient who has just turned 65 and who is generally very healthy and active. I'm not going to counsel them in the same way. I'm going to talk to a 64 year old who's technically not at higher risk, who has myriad health problems. So population level data is one thing and then individual risk calibration and counseling.[00:11:58] EO: Yeah, and I think the piece of this that my senses provoke so much anxiety and discomfort in people is that it is true that, and I don't think you do this, but it is, I think, an experience people either have or fear having in their doctors. They'll be weighed, their BMI will be calculated, and then they'll be told, you know, well, you just, you edged up above, you know, 20, now you're 25.1, and like this is how we're going to define you, and that becomes such an important, like, number in the conversation, and so salient, and the words, I mean, the words we use, overweight versus normal weight, obese, those take on an attention and a meaning, and they didn't just label them BMI category one, BMI category two, which, Maybe would have been more helpful.[00:12:46] You're really using words that suggest that there's a way to be, which is normal, and then other ways to be. And that, that's, it's just not helpful. It's not, I don't think it's a helpful part of counseling. It starts people off on, on a bad, on a bad foot.[00:13:00] LM: Yeah, I mean, I think people, for better or worse, look at doctors as authority figures and people who, whose judgment matters. And if you have a doctor who is doing a little tsk, tsk, tsk, ooh, you're getting up there, that has real power in many ways. And so I think that has real power and can do real harm.[00:13:20] Which is not to say that doctors shouldn't be honest about the data in that patient's situation and what they could do and help to arm them with tools and information to be healthier. It's to say that shame is not appropriate or meaningful in any space, not to mention[00:13:37] EO: Yeah, and I think the other, the other piece that I sort of spent some time on in, in this, and is actually quite closely related to stuff I work on, is that it's actually, It's very hard for most people to lose weight. Like, we know, I mean, we can sort of put Ozempic, Wegovy aside, but for people just changing diet, changing habits, consistent long term weight loss happens for a very small share of the population.[00:14:04] And so, wh…
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