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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.
is a Professor at Brown University, a best-selling author, and a leading voice in health economics. In her wildly popular newsletter, , 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, when we sort of start with the advice, you should lose weight, which people get, you know, in these situations, often that's just not possible. So it's like giving people a set of advice that they just... They're just going to fail on and then giving it as if, well, if only you could have this kind of willpower, if only you could achieve this, like that would be so important.
[00:14:24] I think the whole dynamic ends up in a place where you're giving people advice they can't follow based on a number that may or may not be that meaningful and isn't very nuanced, and you can easily see why that generates frustration, sadness, discomfort, lack of productive conversation with your doctor.
[00:14:43] And then by the way, turns off your ability to have a productive conversation because now we're like in defensive. Now you're like, well, you know, screw you, don't tell me what to do. What do you know?
[00:14:54] LM: Right? If we learned nothing else during the pandemic, that trust is precious. And when you don't have trust between the doctor or patient, and there's a moralization of human behavior, we're just at a standstill. And so how do you see the data that you've pulled together in this piece and before this piece helping people, individuals who are reading your stuff and then going to the doctor's office, understand better what their weight.
[00:15:21] EO: The piece I pulled out at the end that I thought was really meaningful was, in this piece I'm actually pulling data from the NHANES, the National Health and Nutrition Examination Survey, which is a very big survey of, of people, it weighs them, it measures them, collects a lot of biomarkers, which is why we can say all this stuff about, about health.
[00:15:39] They also collect information about their exercise. And so if you look at people, if you sort of take a, a second, uh, almost a second metric of health and you ask like, okay, does this person do like some, some moderate amount of exercise a week and it's like some cutoff and you look at that relationship.
[00:15:57] One of the things I show in the piece is that doing more exercise is correlated with better metabolic outcomes, better kind of health outcomes in various ways. And it's quit informative on top of BMI, and so people who are doing sort of exercise who have a BMI of like 40 actually have sort of similar metabolic health to people who like aren't doing any exercise and have a BMI that we would consider, you know, normal or, or thin.
[00:16:26] And so I think for me that has sort of two pieces of it. One is that it just again emphasizes like this is one other thing you could like if you said like you can only learn two things about people It's like well, how much more could I add with a second thing? Well, actually like quite a lot the characteristic knowing somebody's BMI and whether they have exercised rigorously or moderately in the last week that tells you a lot more about their health than knowing their BMI alone You could add on top of that smoking… it's just one simple illustration of like how much more you could learn if you ask some more questions The other thing, and here I'm going to reveal what my husband is always saying, it's just like, just because you like to exercise, fine.
[00:17:08] But like, actually, I think we should tell people to exercise. I think that we spend too much time telling people to lose weight with their diet, which is something we know is really difficult, and I think we should spend more time telling people, like, you should go take a walk after, like, try to walk for ten minutes every day.
[00:17:27] You know, actually, it's not saying, like, you need to go run a marathon. But just some aerobic exercise. I think we have a lot of evidence from a lot of different places that that's associated with better health. And I think if we started telling people that and talking about that, we would then get to the questions like, well, how can we make it possible for everyone to do that?
[00:17:45] How can we make there be safe places for people to do that? How can we increase access to sports? How can we be in a position where everybody is welcome to... to go running no matter what, you know, their race or body size or anything? And I think that's, you know, for me, that's something that's pretty, that's pretty important. And I think we're kind of missing with this focus on food.
[00:18:08] LM: I totally agree. And what I love about the NHANES data is what you earlier said, which is that there's an incredibly tight correlation between the amount of exercise and health outcomes, even more than BMI and health outcomes. So when I'm talking to a patient who wants to lose weight or, you know, Needs to lose weight, perhaps I often tell them, let's not think about the number.
[00:18:35] In fact, I commonly say, let's not think about the number. That's not our end point. And, and I'm not saying that to be politically correct, to pussyfoot around hard conversations is because the number on the scale is immaterial. When we were talking about this whole person, we are the complex sum of these integrated parts.
[00:18:57] And you can, as you said have a BMI of 40, which is technically obese. But if you are exercising on a regular basis, first of all, your mood is better, your sleep is going to be more efficient, your blood sugar control is going to be better, your blood pressure is going to be better, most likely. And so, I focus, with my patients, less on the number and more on the behaviors.
[00:19:21] The relationship with food, not just what you're eating. The cadence of how you're eating. Sometimes you don't need a fancy diet, you just need to have lunch. I just wrote a piece about that. Lunch is an underrated food group, like eat lunch. Honestly, that is huge. Sometimes we don't need to, you know, go to the doctor and be told that our weight is technically higher than it should be.
[00:19:43] We need to be given materials and information on the benefits of exercise. Not just on our weight, but on our mental health, our metabolic health, our cognition, and not just... Are you told to exercise, but to help people figure out where to put it and how to incorporate it in their everyday life. Because as you know, telling someone to exercise is one thing, helping them figure out what to do is another.
[00:20:10] So I think you're absolutely right, Emily. We need to treat people, not just as a set of metrics and data, but as people. And as you know, from your research, human behavior is complicated. We do things that don't serve us all day long. Even doctors do, which is again, ridiculous, why I would shame anybody for a behavior that's part of the human nature.
[00:20:30] So to do a lot of shooting with patients or to say you should do this is less productive than to say like, how do you think you could incorporate a little more movement because of the data on the benefits of regular movement into your whole health?
[00:20:44] EO: I actually think, you know, when we do this kind of counseling and when people hear this counseling and they hear, they sort of hear the phrase diet and exercise, like you should improve your diet and exercise. They think of that as improve your diet and exercise so you'll weigh less. And that's the link we should sever.
[00:20:59] It would be, I think there's a place to say, improve your, let's think about are there changes you could make to your diet that would make you feel better? Are there ways for you that you could incorporate exercise, which by the way, like 10 minutes of walking slightly faster than you would otherwise, that's exercise.
[00:21:16] That's an exercise activity, so just like making it clear that these things are possible. But also without saying, and if you did that then the number will look better on the, no, if you did that maybe some of these elements of health, metabolic health, maybe some of this would improve, your sleep might improve, your mood might improve, that's what we're aiming for. We're not aiming for some number.
[00:21:37] LM: That's right. And by the way, when you're sleeping better and your mood is better and your dopamine hormone axis is being triggered by the lights of being outside and feeling more fit and getting the endorphins going that is good for our metabolic, metabolic health too. But I also want to be clear that I don't shy away from talking about a number when it is relevant.
[00:22:00] So if somebody has bilateral knee osteoarthritis, bone on bone, and their BMI is 40, and they're resistant to, you know, getting a knee replacement, we have to talk about weight. So it would be irresponsible for me to say, oh, weight loss isn't going to matter to this gravity-dependent set of joints. And so that is where it gets really hard, but it is where I actually like for me it's my like superpower is never to have judgment about it because by the way when you have bone-on-bone arthritis in your knees As a result of age and genetics and weight all together you can’t exercise and You gain weight more easily.
[00:22:43] And so this is what happens. So there's no shame about it. It's just, let's figure out what to do. But we have to talk about the number, not just the number, but we have to talk about what weight might make sense to that offset pressure on the knee.
[00:22:56] EO: Yeah, I mean, that's such an interesting, like, it's, this conversation is so hard because it takes, like, it's so hard to have that conversation. And I bet you are really good at this, but I think for me, it's very hard to have that conversation without it feeling like shame because of the, as opposed to just saying, look, there are a bunch of things, like, there is a physical reason why this, this number matters, not because this number has to do with whether you're a good person or not a good person or have willpower or whatever, it's just like, this is putting pressure on your knees.
[00:23:23] LM: Well, and that's why I'd really like to reinvent the healthcare system to have doctors incentivized to have more time with their patients to understand their story and to build trust and rapport and for patients to feel comfortable and then to train doctors on sensitivity on these subjects. Which, by the way, doctors went into medicine, the field of medicine to do that, but it's just people don't have time and then people don't trust and then there's diet culture and then it's just lose weight, exercise more, see you next year.
[00:23:50] EO: This is totally off topic. I mean, it's a little bit off topic, but, but one of the things that's been pretty effective in, you know, obstetrics is these group prenatal care. People have exactly this sort of same complaint about, like, there isn't enough time to talk about all the issues that have come up, da, da, da.
[00:24:05] And so they do these things where it's like six people, but you get two hours, you know, and we do, like, there's this sort of examination component that happens, like, that's short for each person, but then we all, they, people all talk together, and it turns out to actually be, some good evidence on the relationship between that and preterm birth, particularly for black women.
[00:24:20] So I wonder if there's like, I almost think there's like a parallel care model, where it's like, we have a group of people here for counseling about, you know, whatever it is, improving their heart disease metrics or something.
[00:24:33] LM: Yeah, stay tuned for some courses I'm going to be offering in 2024. One of my little kind of mantras is that health is about more than BMI. It is about having awareness of our health ecosystem, which includes ur story, it includes our data, it includes understanding our genetics, and then sort of a laddering up to acceptance of the things we can't control.
[00:25:01] Maybe we are predestined to have a higher-than-ideal body mass index because of our genetics. And we have to accept that. We have to accept that we are predisposed to diabetes. And then agency over the things we can control. So, arming yourself with tools and information to carve out space in your life to work on the things you have control over, which are a lot.
[00:25:26] But if you're stuck in the acceptance bucket where you're not accepting hard parts of your genetics or your story that you can't control and you're then listening to a lot of kind of wellness gurus who are telling you that, you know, thin is better or whatever, even just all this messaging. And then you're spending a lot of brain space trying to accept things you really need, or trying to control things you can't control, that's where people run into trouble, and that's where shame is born, and that's where people, frankly, binge on things like food and alcohol, and that's where we land in trouble. And so if we could just help people understand they're not alone, they're human, and that we all have our challenges. One of them, for a lot of Americans, is weight.
[00:26:12] And that they're not alone, and that there are things they can do to be a lot better off. So... What was the takeaway from this piece you wrote? Like, what was the reaction? Because, as you said, like, there's sort of two camps. It's like health at every size, there's a movement, which I agree with in many ways, except that there are certain medical realities we have to acknowledge.
[00:26:32] And then there's the sort of, weight is genetic, and there's nothing you can do about it. And, I mean, there's just, there's just these false dichotomies.
[00:26:39] EO: So I think like with most things, most people are in the center. And so this kind of like, I think that many people found this interesting. You know, I'm not sure everybody thinks about this data quite the same way, and sort of seeing some graphs about it, it made some people think. A bunch of the comments were like, yes, like I started exercising, and I felt like this is very validating, because like, that, you know, that totally changed, but then my weight didn't change, but still I feel better, and I was trying to understand that.
[00:27:08] So there was like some good stuff there. And then I did get, certainly, some people who said, you know, talking about BMI at all is very fatphobic and I am, like, I will say, like, I'm a relatively thin person and so I think, you know, I don't know, I guess that's part of, part of it. And then certainly there were people on the other side who said, you know, this whole thing is like, you know, anybody who's overweight is just, you know, is just lazy and I don't agree with that at all. But some of those people fought with each other and, you know, that's what comments are for.
[00:27:39] LM: That's what's comments are for. And that is why Emily Oster is here. Emily is here to help us get to these story issues, and ask the questions that... People are wrestling with every day, like, can you have a glass of wine when you're pregnant? Can you have bluebean cheese when you're pregnant? Can you jettison some of the shame about parenting and the parenting industrial complex?
[00:28:01] And thank God for you because I think you're doing so much good, Emily, and you're reassuring people based on evidence. You're not reassuring people for the sake of reassuring them for you to look good. You're reassuring them because you have the data to show. How to calibrate risk to, or sort of how to calibrate anxiety to the actual
[00:28:21] EO: Yeah, I mean, I see a lot of what I try to do is sort of help people see what those risks are and make the choices that work for them, which [are] going to reflect our own risk tolerances and preferences and, and what's important to us.
[00:28:33] LM: Yeah. I mean, at the end of the day, as we talked about during COVID quite a lot, it's about framing risk. It's not about telling people how to feel or telling people how to choose. It's about framing risk. And then it's like, you do you, and that's fine. And if you do something that's not healthy for you, that is fine too. As long as you're armed with the data, then that, that, that is, that is great. Emily, thanks for joining me. And by the way, how can people sign up for parent data?
[00:28:56] EO: So, parentdata.org, you can find me there, we have a newsletter that goes out, we have an enormous volume of writing for pregnant people and parents and, and some things for people who are not parents, and we have like a little search AI, so parentdata.org is the best place, or you can find me on Instagram at profemilyaster.
[00:29:20] LM: Thank you all for listening to Beyond the Prescription. Please don't forget to subscribe, like, download, and share the show on Apple Podcasts, Spotify, or wherever you catch your podcasts. I'd be thrilled if you liked this episode to rate and review it. And if you have a comment or question, please drop us a line at info@lucymcbride.com. The views expressed on this show are entirely my own and do not constitute medical advice for individuals. That should be obtained from your personal physician.
Is There a Link Between BMI & Health?