The science of losing weight

When it comes to weight loss, there are many misconceptions about what works. So if you want to lose weight this year, here's what the science says about the potential health benefits, GLP-1 drugs, exercise and more. Sign up for Life Kit's Guide to Building Strength here: npr.org/stronger http://npr.org/stronger Follow us on Instagram: @nprlifekit https://www.instagram.com/nprlifekit/?hl=en Sign up for our newsletter here. https://www.npr.org/newsletter/life-kit Have an episode idea or feedback you want to share? Email us at [email protected] mailto:[email protected] Support the show and listen to it sponsor-free by signing up for Life Kit+ at plus.npr.org/lifekit http://plus.npr.org/lifekit See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:00Speaker 00

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• 0:16Marielle Segarra?

  Hey, it's Marielle. Before we start the show, let's play a little game. What helps you live longer, improves symptoms of depression and anxiety, cuts your risk of chronic illnesses, bolsters your immune system, strengthens your bones, and reduces chronic pain? Strength training. And that's not even a full list of all the benefits. To help you get started building muscle, we created a newsletter series. No experience necessary to get going. Sign up at npr.org/stronger or find the link in the episode description.

• 0:53Marielle Segarra?

  You're listening to Life Kit from NPR.

• 1:00Marielle Segarra?

  There's something we don't talk about much on Life Kit, and that's weight loss. There are a lot of reasons for that. One is, it feels like conversations around health and fitness can focus too much on losing weight, when our physical health is more complicated than that. Also, this show is about a life well-lived, and there's so much more to that than how many pounds you weigh or how your body looks. That said, we felt like this was the time to talk about it again. Losing weight is a very common New Year's resolution, but it's complicated, and there are a lot of misconceptions about it. For instance...

• 1:35Speaker 02

  Often, people think that if they just can make some lifestyle changes, some hacks of their metabolism or something like that for a period of time, and they can reach some goal weight that they might set out for themselves, and then they can relax after that. And I think that what most people need to realize is that that's not how weight loss works. If you want to maintain the weight that you might end up losing, then you're going to have to incorporate those lifestyle changes permanently into your everyday life.

• 2:06Marielle Segarra?

  This is Kevin Hall. He's a nutrition and metabolism researcher, formerly at the NIH. He studies weight loss specifically. And he says another thing people tie strongly to weight loss is exercise.

• 2:18Speaker 02

  Oftentimes, people will start an exercise program around the beginning of the year and join a gym or something like that, or hire a personal trainer. And because they've so tied the idea that one of the benefits of exercise is weight loss, and for some people it might be, others will get very discouraged if they don't see the numbers on the scales move. And they might actually start quitting the exercise program, which would actually have independent benefits for all sorts of aspects of health, regardless of whether or not it affects your body weight at all.

• 2:48Marielle Segarra?

  As we talk about all the time on the show, we need to move our bodies regardless of what we weigh. On this episode of Life Kit, I talked to Kevin about the realities of losing weight. If that's a goal for you, we're going to give you some facts to consider and takeaways based on the research.

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• 4:27Marielle Segarra?

  Kevin, this is a time of year when a lot of people are thinking about weight loss, but before someone pursues that, who benefits from losing weight?

• 4:37Speaker 02

  Nowadays, given that there's such a high degree of prevalence of overweight and obesity in this country, I would say the vast majority of people can benefit clinically from losing a little bit of weight. For some people, that doesn't require much weight loss, maybe even 5% body weight loss. For others, it might require more weight loss to receive the very large benefits that people with obesity often see with weight loss. But it's important to realize that just by looking at somebody, you cannot tell whether or not they are experiencing the metabolic side effects of having excess body fat. That can kind of kick in at various different body sizes, and some of these body sizes doesn't necessarily tell you anything about their health status. But the vast majority

• 5:21Speaker 02

  of people who end up losing some weight will see some metabolic benefits.

• 5:25Marielle Segarra?

  And when we say metabolic benefits, what does that actually mean?

• 5:29Speaker 02

  It means that they'll improve their glucose control, they'll improve their blood lipid levels, which are related to cardiovascular disease. Many aspects of several forms of cancer have been related to excess body fat, and so decreasing body fat can result in decreasing risk for various forms of cancer. But mostly, these sorts of metabolic diseases like heart disease, stroke, diabetes, and things like that.

• 5:56Marielle Segarra?

  How clear is the research that it's weight loss or gain that matters here?

• 6:02Speaker 02

  Yeah, no, it's a great question. And for some outcomes, it's much more clear than others, right? So for some outcomes, like type 2 diabetes, which is causally related to your body's ability to use the hormone insulin, and whether or not your body is making enough insulin, that sort of process and the sort of pathophysiology by which diabetes develops and insulin resistance develops is becoming more and more clear. And it seems like excess body fat in the wrong places, in other words, in organs like the liver, or the muscle, or around your pancreas. Is causally related to the sort of progression of this metabolic disease and the development of type 2 diabetes.

• 6:45Speaker 02

  And so the ability to kind of remove fat from those locations, and unfortunately, there's no targeted way to do that right now. It means you sort of have to remove fat from the entire body.

• 6:57Marielle Segarra?

  Takeaway one, there can be real health benefits to losing weight. Though, as Kevin said earlier, you don't need to lose a lot of it to start seeing some of those benefits. We're talking about 5% of your body weight. I asked him more about this. Okay, so let's say you're 220 pounds and you lose 11 pounds. That could be plenty to get the metabolic benefits we're talking about?

• 7:20Speaker 02

  Well, you could begin to see some of the metabolic benefits, yeah. I mean, I think the point is, is that it depends on where you're starting. It depends on your level of disease to begin with. And obesity is now considered a disease in its own right, so it's not just increasing the risk of other diseases. That 5% weight loss, you can already begin to see some of those metabolic benefits in improving insulin resistance, for example. But of course, it is dose dependent. So in other words, the more weight that people lose, especially when you're starting off with very high amounts of body fat, the more metabolic benefits you tend to see.

• 7:57Marielle Segarra?

  I mean, that makes sense. I just am cautious of telling people, you know, the more and more weight you lose, the healthier you'll be, because at a certain point, they're going to be tipping into potentially eating disorder category, or someone who's just like not getting the nutrients that they need, for instance, right?

• 8:17Speaker 02

  Right. No, I think it's really important that people personalize this sort of discussion, right? I've been focusing on folks who clearly have excess body fat and can stand to lose quite a bit of weight as a result of that and see these benefits. But you're absolutely right. One of the challenges with discussing weight loss and discussing obesity in general is that there's a huge sort of societal and stigmatizing notion about people with obesity and people with excess weight. And there's also this cosmetic aspect, right? This pressure to look a certain way, which you don't get with other diseases like type 1 diabetes, for example. It's not associated with anything that you can observe from the outside.

• 8:58Speaker 02

  So I think you're right in pointing out that there are other factors at work here. When we're talking about weight loss, both in terms of people with obesity receiving the stigma from the medical establishment even, as well as everyday folks, and just the risks of conflating many of the cosmetic benefits that people believe they're experiencing when they're losing weight with the health benefits. And then you're right to point out the risks of people developing potentially disordered eating behaviors as well, which is obviously problematic.

• 9:31Marielle Segarra?

  It sounds like something to check in with a doctor you trust about a healthy target for you.

• 9:37Speaker 02

  Absolutely.

• 9:38Marielle Segarra?

  You've mentioned losing body fat or carrying around excess body fat as opposed to weight specifically. I wonder, how are those things different?

• 9:48Speaker 02

  Yeah, no, it's a great question because obviously body size differs between people quite a lot, just looking at height. And people who are taller obviously typically weigh more as well. And so one of the questions is, what is your body composed of? How much of your body is muscle mass? For example, how much of it is fluid? How much of it is these various different organs? And how much of it is body fat, which can be stored in healthy places and can be stored in places that are not so healthy and cause some of these adverse metabolic consequences? So yeah, what your body is made out of and your particular body fat level and where you're carrying your body fat can be very important to know when it comes to risk

• 10:33Speaker 02

  of these different metabolic complications.

• 10:36Marielle Segarra?

  Are there reliable ways to measure body fat? And is that worth doing?

• 10:41Speaker 02

  There are reliable ways. They end up being relatively expensive for many people and not all that well available. So most people will use the simple measurement of their weight divided by their height squared. And that's the so-called body mass index. And it's correlated quite well with body fat for many people. But there are exceptions and there's still quite a bit of uncertainty about that. And the other thing that's important to know, too, is that even people who do end up having high levels of body fat, where that fat is being stored in the body, is it being stored in places which are more or less inert and are not affecting health

• 11:22Speaker 02

  very much, or are they being stored in places that are more metabolically dangerous? Your total body fat measurement will not tell you much about that. That's why some physicians are now starting to use things like the waist to hip ratio. If your waist is much, much larger than it should be for your hip measurements, that means that you're probably carrying quite a bit of fat around your abdomen and in particular your liver, which might be more metabolically dangerous than carrying it on your thighs, for example.

• 11:51Marielle Segarra?

  And I imagine you can also be considered at a healthy BMI or at a healthy weight according to your doctor, but then you have high cholesterol or high lipid count specifically, or you develop type 2 diabetes. And so I feel like that's important to point out.

• 12:13Speaker 02

  That's exactly right. And it turns out that, you know, different ethnicities have different sort of BMI thresholds, which people talk about as being particularly risky. So men, especially from South Asian descent, will look perfectly fine from a BMI perspective, but at a much lower BMI, they will generally start to see these increased risks. And that seems to be because they're storing quite a bit of their fat in their visceral organs and their liver in particular. So, yeah, so just looking at the scale on its own is probably not sufficient. And even just looking at the scale with your height factored in with BMI probably isn't sufficient either. You do have to kind of look under the hood, so to speak, and make sure that your metabolic

• 12:56Speaker 02

  health is aligning with your so-called healthy BMI.

• 13:01Marielle Segarra?

  Takeaway two: Weight is not a cut and dry indication of health. Someone with a lot of muscle can weigh the same as someone with a lot of body fat and have very different health outcomes. Also, it can make a difference where your body fat is stored. For instance, if you carry a lot of weight around your liver, that might be more risky to your metabolic health than carrying it on your thighs. One common screening tool that doctors use to estimate body fat is BMI, Body Mass Index. It's simply your weight divided by your height squared. BMI was developed by a statistician in the 1800s and used in population studies to analyze data about men. It was later adopted by the insurance industry to assess risk. Now you'll find it on almost all of your medical records,

• 13:46Marielle Segarra?

  even though it is a highly imperfect measurement and it doesn't take into account muscle mass, bone, or where your fat is stored. Researchers have been looking for a more reliable metric. A person's waist to hip ratio is one promising measure. And another is BIA. That's a type of analysis that uses an electrical current to estimate body fat. There are scales that do this and cost a few hundred dollars. One other reminder: Even if you are considered healthy according to your BMI, you can still have conditions like high cholesterol, diabetes, and heart disease. So it's important to get routine physicals and screenings anyway. We'll have more Life Kit after the break.

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• 15:23Marielle Segarra?

  The conversation around weight loss has shifted a lot in the past few years with Ozempic and other drugs like it. I wonder, what are your thoughts on these drugs and who do they work for?

• 15:33Speaker 02

  That's right. I mean, in the past, we had lifestyle interventions that have led to modest amounts of weight loss and, like I said, some benefits for many, many people. But there are others that could benefit from more weight loss, but we're not achieving that benefit because it just turns out to be so darn hard for folks to kind of incorporate major changes into their everyday lifestyles. And then there's the bariatric surgeries where we've seen, you know, huge amounts of weight loss and these large benefits. But of course, it's a pretty traumatic procedure to undergo. It's expensive. Sometimes you will qualify for it through insurance, but it's a major thing. And so it's also had relatively limited uptake over the years.

• 16:14Speaker 02

  And this new class of weight loss medications now has, offers something in between, right? Offers the sort of 15% to 20% average body weight loss. Comes with many of the benefits of bariatric surgery, but not to the same extent. Also tend to be quite expensive for many people to obtain, and they're not without risks in some folks and side effects as well. So the way I sort of see it is that they're certainly a welcome option for many, many people. But of course, it's not something that can be handed out like candy either. It's a, needs to be under a watchful and well-trained physician. And unfortunately, I think we see right now a lot of physicians who are not well-trained

• 16:57Speaker 02

  necessarily in obesity management. And we even see, you know, a lot of people getting these drugs with very little oversight. And I think that's, that can be quite worrying, especially when they're not even using the grand names of some of these drugs or these compounded drugs sold by pharmacies, which are quite worrying for many physicians.

• 17:20Marielle Segarra?

  Takeaway three. GLP-1 drugs like Ozempic, Wegovy, and Monjaro can be helpful tools, especially if someone is trying to lose a lot of weight or they're at the point where they're also considering bariatric surgery. But like any other drug, they come with risks and side effects. You also need to keep taking them to keep the weight off. If you do start taking these drugs, make sure you're doing it under the supervision of a doctor who's well-versed in obesity management.

• 17:48Marielle Segarra?

  What would you say are the most persistent myths in weight loss?

• 17:53Speaker 02

  I think the most persistent myth when it comes to weight loss is still the idea that this is just a matter of willpower, that the reason why people have excess weight and excess body fat to begin with is some sort of moral failing, and if you just kind of were to make some simple changes in your life, that you would be able to achieve a "healthy" weight, and it's because of some sort of moral failing that people have experienced excess body fat. And I think that that line of argument has been kind of demonstrated scientifically to be clearly false, that somewhere between 40 and 70% of the variation in body size

• 18:38Speaker 02

  is due to genetics. And in the past several decades, we've experienced a sort of shift in, in particular, our food environment that has caused the increased prevalence of these diet-related chronic diseases. And still, I think, many people feel like if there was, people just took more personal responsibility, that they could easily, or maybe not easily, but they could will their way to a more healthy weight, and that's clearly not the case.

• 19:07Marielle Segarra?

  I think you hear this a lot when people say, "Oh, it's just calories in versus calories out."

• 19:12Speaker 02

  Yeah, the idea that we had complete control over both of those variables, right? Both calorie intake and calorie expenditure, the number of calories our body is burning through metabolism and physical activity, as well as other functions, those things are under biological control, and often operating below our conscious awareness. And we know that many of the genes that are kind of increasing the risk of obesity and things like that are genes that are primarily expressed in our brains, and are fundamentally related to appetite regulation. And so, these are biological factors that we have very limited control over.

• 19:53Marielle Segarra?

  Takeaway four: There's this idea that all you need to lose weight is willpower. But that's a misconception. A lot of the factors that contribute to our weight, including genetics, are out of our control. So if someone does want to lose weight, what are your top tips based on the research?

• 20:13Speaker 02

  I think focusing on weight alone might be a little bit of a mistake. I think it's better to focus on improving the healthy aspects of your lifestyle that you can fit into your lifestyle on a regular basis. And then exercise is one of those top things that might not lead to very much weight loss in many people, but it's clearly going to have health benefits. Another aspect is just improving the overall quality of your diet, eating more fruits and vegetables and whole grains and legumes and things like that, and avoiding saturated fat and sodium and sugar and refined grains and ultra-processed foods and those kinds of things. If you can kind of do that on a regular basis without spending too much money or having to prepare all these meals, and you can actually have the interest

• 20:58Speaker 02

  in doing that and have the skills to do those things, that would be great. But again, on a case-by-case basis, many people are unwilling to make these huge changes just because they can't afford it, there's not enough time, they have competing pressures in their life. So there's lots of advice that you could give people, but the real trick is figuring out what types of advice to improve their overall lifestyle. Many of those things will lead to weight loss. Some of them won't lead to much weight loss, but they will all sort of improve people's health and how they feel. So I tend to like to try to decouple those lifestyle changes that people should think about incorporating and keeping persistent throughout very, very long time periods from focusing on the number on the scale.

• 21:44Marielle Segarra?

  Takeaway five. Focusing solely on losing weight might not be the best resolution for you. Instead, if you're not already exercising regularly, start. Incorporate strength training once or twice a week. Do some cardio. The CDC recommends 150 minutes a week of moderate intensity movement, like brisk walking or jogging, dancing, cycling, chasing your dog around, shoveling snow, whatever you like. Also, improve the quality of your diet. Cut down on ultra-processed foods and eat more fruits and vegetables. These things may or may not help you lose weight, but they'll definitely make you healthier. Kevin, thank you so much for this.

• 22:23Speaker 02

  For sure. My pleasure.

• 22:27Marielle Segarra?

  All right, time for a recap. Takeaway one, there can be real health benefits to losing weight, but you don't need to lose a lot of it to start seeing those benefits. We're talking about 5% of your body weight. For a 220-pound person, that would be 11 pounds. Takeaway two, one common screening tool that doctors use to estimate body fat is BMI, Body Mass Index. It's simply your weight divided by your height squared. It is a highly imperfect measurement, and it doesn't take into account muscle mass, bone, or where your fat is stored. Researchers have been looking for a more reliable metric. One option is looking at someone's waist-to-hip ratio, and another is using a scale that estimates body fat using an electrical current.

• 23:10Marielle Segarra?

  Takeaway three, GLP-1 drugs can be helpful tools, but like any other drug, they come with risks and side effects. You also need to keep taking them to keep the weight off. Takeaway four, there's this idea that all you need to lose weight is willpower. That is a misconception. And takeaway five, focusing solely on weight loss might not be the best goal for you. Instead, consider regular exercise, strength training and cardio, and improving your diet. These things may or may not help you lose weight, but they will definitely help your health overall. And that's our show. Hey, speaking of strength training, are you looking to get stronger this year? We have a special newsletter series to help you start your own strength routine.

• 23:53Marielle Segarra?

  You can sign up at npr.org/stronger. This episode of Life Kit was produced by Claire Marie Schneider. Our visuals editor is Beck Harlan, and our digital editor is Malika Gharib. Megan Cain is our senior supervising editor, and Beth Donovan is our executive producer. Our production team also includes Andy Tagel, Lennon Sherburne, Margaret Serino, and Sylvie Douglas. Engineering support comes from Robert Rodriguez. Fact checking by Tyler Jones. I'm Mary El Segarra. Thanks for listening.