How should we measure obesity?


Announcer: Welcome to Stuff Mom Never Told You from HowStuffWorks.com.

Cristen: Hello, and welcome to the podcast. I'm Cristen.

Molly: I'm Molly.

Cristen: So Molly, it's after the holidays. We have survived the holiday season.

Molly: I don't know - Martin Luther King Day is coming up.

Cristen: I know, thank goodness, another holiday to look forward to. But it's around the holidays and around this time, especially after the holidays, with New Year's resolutions and everything, we start kind of assessing our weight, our physical fitness, seeing what trouble spots we might need to work on, which brings to mind a little measure called body mass index.

Molly: Yeah, and it's pretty easy to find out your own body mass index. You go online, you Google this, you'll be able to enter your weight and your height, and find out a number that's between 18 and 35ish, is it?

Cristen: Something like that.

Molly: Sort of where the calculations kind of run, and if it falls within a certain range, then you're considered normal, overweight, or obese.

Cristen: Yeah, and this seems like a pretty quick, simple assessment of your weight, but there was some controversy earlier this year about how one university was using BMI to determine whether or not students could graduate.

Molly: Right. This was at Lincoln University in Pennsylvania. It was the end part of 2009, so you probably heard about this story. The school was requiring students with a body mass index of 30 or above to take a fitness course in order to graduate, and this raised a lot of controversy about whether it's a school's responsibility to tell a person that they might have a health problem.Students were saying that this shouldn't be a requirement to graduate, that their academic record should be, but one of the factors that always comes up, I think, when BMI is involved, is that it's not the most accurate thing. Now to make sure that they were really getting students who they considered obese, the school went on to measure the student's waist, hoping that that would weed out people like athletes who have higher weights, but are still healthy for their heights.

Cristen: Right. Because people with really high BMIs in the overweight and obese category might be at a higher risk for things like heart disease and type-2 diabetes, so the college was arguing, "Hey, we're trying to do this for our students - better health in the future," but we recently found out that because there was so much hubbub surrounding this issue, the school just basically dropped it. But the issue of whether or not BMI is actually a good predictor of health is still pretty controversial.

Molly: So let's talk about it. Do you want to talk about all the ways we can measure obesity, Cristen?

Cristen: Yeah. Let's talk about like what exactly the BMI formula is and go from there. Your BMI is your weight divided by your height squared, times 703.

Molly: Now wait - that all depends on whether you're doing metric system or just standard, right?

Cristen: Yeah. This is just -

Molly: Because I hate metric.

Cristen: Yeah. For people in the U.S. of A. -

Molly: Like me, who hate metric.

Cristen: Like Molly, anti-metric Molly - new nickname - that's the formula. There's another formula for the metric system, which -

Molly: I think is actually easier. I don't think you have to do anything with 703.

Cristen: Probably is. Metric is far easier and makes a lot more sense. So that is the BMI formula, but like you said, there are a few other even more reliable ways to assess your body fat content.

Molly: Now, we just mentioned that Lincoln would measure a student's waist, and this is known as the waist-to-hip ratio, which is getting a lot of attention lately as a hip - ha, ha, ha - new way to measure obesity. What you do here is you take a tape measure, and you measure your waist at its smallest point and your hips at their largest point, divide them, and you should get a ratio. And they don't know yet what the perfectly healthy ratio is, but they're saying that if you're a female, if the ratio is less than one, then generally you're okay.

Cristen: So we've got BMI, we've got waist-to-hip ratio, and we also have the old pinch test. That's basically where you take the calipers to measure the folds of skin in certain spots in your body. This is not a fun test to take, Molly, and I can speak from experience. I had to take a pinch test in, I believe it was, 11th grade in health class in high school, and -

Molly: Traumatized, you sound.

Cristen: It wasn't traumatizing. To me, the idea of going to gym class and having your fat pinched was not a good idea for 16- and 17-year-old girls, but that's another way to do it.

Molly: But it's not very accurate. That's the thing - if it's just some gym teacher who's borrowing the calipers from the health department, you can get a vastly incorrect reading. We were reading in U.S. News and World Report that let's say you've got 25 percent body fat, or that's what the caliper shows that you have, that could be anywhere from 22 to 28. It's got a big margin of error if you're not using the pinchers exactly right.

Cristen: Yeah.

Molly: So something that's a little bit more accurate, according to U.S. News and World Report, is something called the bioelectrical test. This is where a technician will attach electrodes to one hand and one foot, and they run a harmless - let me specify harmless - radio frequency pulse through your body to measure it's water content.

Cristen: Ooh, space age.

Molly: Space age, but again, I guess no way of measuring body fat is going to be tons of fun, but I can't imagine having radio frequency running through me would be good. But this is at a lot of health clubs, medicine clinics; it's not very available, let's say, to the general public. Also not very available is something called the BOD POD.

Cristen: This is my favorite one, if only for the catchy name.

Molly: I would love to have a BOD POD. It's an egg-shaped chamber, and you climb in. You sit there for 20 seconds and it can measure air displacement and tell you exactly how much body fat you have.

Cristen: So the BOD POD is pretty spot-on with this it seems like so far.

Molly: It's sort of the golden standard, and as most things that the golden standard are, it's very expensive, so it's only at a few hospitals. It's really not available to the general public, which is why the general public is still left finding a body mass index calculator online and using that to figure out how much body fat they have.

Cristen: Now for the last test, Molly, the immersion test, this one seems like the most pleasant one to do because you basically just get in a pool of water and get dunked a few times. First you will expel all the air from your lungs, and they dunk you in a pool half a dozen times, and it says that it under or overestimates your body fat by only 1 percentage point, so still pretty accurate.

Molly: It is, but that is just the recipe for the worst day ever to me.

Cristen: Getting dunked?

Molly: Let me go jump in a pool for an hour and then hear how much body fat I have. If that's not a recipe for overeating ice cream, I don't know what is, but if you've had any of those tests, I want to hear about them. If you've been in a BOD POD, I want to know how cool it is.

Cristen: But here's my question, though, Molly. We have all of these other ways to assess body fat -

Molly: That are very accurate.

Cristen: That are far more accurate, but Molly, my question is, we have all of these different options for measuring body fat, and a lot of which has far more accurate results, however, BMI is still our go-to measure.

Molly: Right. That's what they were using at Lincoln. Whenever you read articles about health risks, heart disease, things like that, people are always going to say, "Look at your BMI." But why? Why are we looking at BMI?

Cristen: Well, Molly, should we go back in time, perhaps?

Molly: It's my favorite thing to do on this podcast.

Cristen: Tell the story of the body mass index, which is actually more interesting than this probably sounds at this point, listeners, so -

Molly: Because there's someone involved named Adolphe Quetelet.

Cristen: Quetelet.

Molly: And he's from Belgium, and all good stories start in Belgium. So he's the one who came up with this equation in 1832 not because he had this overwhelming desire to study obesity, but because he was doing this study on normal man. That means he was looking at everything about man that was average to figure out just what the most perfectly average man would look like, from his arm length to his leg length, to his obesity.

Cristen: And I think that we should note that we got all of this great information from an article on Slate. So Quetelet went around collecting all of his data from several hundred countrymen, and he found that there were correlations between a man's weight and height, basically that your weight is going to be proportional to your height. Say if I am 10 percent taller than you, I'm probably going to weigh 10 percent more than you, as well.

Molly: So he makes this pretty decent finding, but it's not like doctors just jump on it immediately to say, "Oh, Quetelet, you've discovered how to measure this." It kind of sits dormant for a while.

Cristen: Yeah, because back then, doctors weren't really linking illness to obesity. The first large-scale studies of obesity and health didn't start until early in the 20th century, with the rise of insurance companies.

Molly: Now, I find this really interesting because in all this talk of healthcare reform, you kind of wonder if we could save a lot of healthcare costs by coming out and telling people, "Hey, you're unhealthy. You need to change your habits," which is what Lincoln was trying to do, the school, so just bear that in mind when you think about what an organization's role is in telling people that they're unhealthy.But here's what the insurance companies do - they want to show their policy holders that yes, you are costing us more if you are overweight because overweight people are dying earlier than those of a so-called ideal weight. You're more likely to get diabetes. You're more likely to get heart disease, and we're paying out the nose for that. So what these insurance companies need, basically, is a quick function to show how body fat is related to your height and weight.

Cristen: Yeah. And back then, they had like the caliper skin fold testing, and hydrostatic weighing with basically the immersion test that we mentioned, but it wasn't until 1972 that a physiology professor and obesity researcher named Ancel Keys published the landmark "Indices of Relative Weight and Obesity," which he studied 7400 men in five different countries to assess different height and weight formulas that correlated to the best measurement of their body fat percentage. And with this study, he found that Quetelet's formula was the best.

Molly: It was the best, but he noted that it was the best at population studies. It was a good way for doctors to get an idea of how a certain populatio n was overweight or not overweight. It was never meant to be used on an individual diagnosis scale.

Cristen: Right. And Keys was the one who renamed Quetlet's formula the body mass index, and then in 1985, the National Institutes of Health started defining obesity according to BMI.

Molly: And what I thought was really interesting in these articles, when the NIH first started using body mass index to define obesity, it was very specific in terms of gender, in that you could have a BMI measure for a woman and a man, and the numbers were different. They were kind of odd numbers like 27.8 was a cutoff for obesity, whereas now everything is sort of on the fives, like 25, 30, 35. That's how they determine if you're overweight or not.But then in 1998, they just wanted to sort of standardize everything, and that means that both men's and women's BMI was measured the same way, despite the fact that women have a lot more body fat. And like I said, everything became on the fives, so it was easy to remember. You knew as soon as you hit 30 on your BMI that that was a bad thing.

Cristen: So not only do we have this measure that was originally intended for population studies rather than individual diagnoses, we also have the NIH coming in and sort of further watering down those standards, so we're starting to see how the BMI might not be the best predictor of your health. Because like you said, just to throw out a couple of things, like BMI is the same for gender, race. There are some differences for children and teens, but for the adult population, a BMI is a BMI is a BMI. It doesn't differ for men and women. However, like you said, women tend to have more body fat than men, and at the same BMI, older people will tend to have more body fat than younger adults, which makes sense.

Molly: They're losing their muscle mass.

Cristen: Exactly. And then, speaking of muscle mass, highly trained athletes, who are very muscular, will probably have a very high BMI that might put them in an overweight category because it's just looking at body mass rather than differentiating between fat and muscle.

Molly: Right. So you can find many articles on the Internet that just cry, "Down with the BMI. It's not very accurate. Please don't go on the Internet and decide if you're overweight just based on a BMI." A really good example of how this can work against you is a New York Times article from 2007 that Cristen found, it's called, "How does your waistline matter? Let us count the ways." Ha-ha-ha. And this woman had a perfectly normal BMI. She didn't have many risk factors for heart disease, but then her doctor whips out a tape measure and does the old waist-to-hip ratio, and finds out that she is actually in a high-risk category for developing some of these long-term health problems.

Cristen: Now, while that New York Times article highlights a couple of individual stories, I think we should also note that there have been a few large-scale studies that have called the BMI into question. For instance, there was a recent one from the National Institutes of Health that compared people's BMIs against results from the bioelectrical analysis that we talked about earlier, and it found, for instance, a big gender gap in these measurements, where with men, the BMI had a better correlation with their lean mass, while in women, the bioelectrical test was a little more accurate predictor. And they basically concluded that the BMI is pretty limited in how well it assesses obesity, and in this case, it missed more than half the people with excess fat. And in addition, the Slate article also mentioned a critique that was published in the journal Circulation that said that since BMI is used in so many of these large-scale health studies that we see, and since BMI might also not be very accurate, we don't know how that's affecting all of this health research that's going on, so this could have a ripple effect into areas beyond just obesity.

Molly: So basically, you can't trust your BMI. It may not be showing that you are overweight; it may be showing that you are overweight and you're actually not, but it doesn't seem to be going anywhere because as we said, it's so easy. Anyone can check their BMI.So right now, the big guidelines, even though the NIH has found it's not the most accurate thing, it, through its National Heart, Lung, and Blood Institute has sort of tried to bring the waist-to-hip ratio more into a three-legged stool, if you will. A three-legged stool of assessing your risk for these long-term health conditions, to try and figure out if you are overweight, is the BMI, plus the waist circumference thing, and then also just evaluating your risk factors.Do you have things like high blood pressure? How's your cholesterol count? How's your blood glucose? Do you have a family history of this? Do you smoke? Do you exercise? So hopefully we'll be coming to a more well rounded view of how we can measure obesity in the future, particularly if schools like Lincoln are going to try and dictate graduation based on it.

Cristen: And it all goes back to Quetelet.

Molly: So thanks, Quetelet, for all your hard work in 1832.

Cristen: Yeah. But unfortunately, Mr. Quetelet, we have manipulated and misused your tool, but maybe we're on the right path now.

Molly: Maybe.

Cristen: Maybe that should be our health resolution for 2010.

Molly: To find a BOD POD, that's mine.

Cristen: So if any of you fair listeners out there have access to a BOD POD, you should definitely email us at MomStuff@HowStuffWorks.com and make Molly Edmond's year.

Molly: I don't know if it would make my year.

Cristen: Well, maybe a week of it? A day?

Molly: Yeah, a day.

Cristen: Make Molly's day with a BOD POD. And speaking of listener mail, why don't we do some of that.

Molly: Okay. So today, Cristen, we're going to read some emails about the women behind Santa Claus, that podcast we did right before Christmas And first off, we need to thank many of the listeners - I'm not going to identify any of them by name because a lot of people caught us on this one - we made fun of the "Goody Santa Claus," the Katharine Lee Bates article, and it sent me back to 11th grade English as soon as our listeners started writing in, but Goody is an abbreviation of the title "Goodwife." So back in those days, I would have gone over to you and been like, "Goody Conger, have you any cookies for me today?"

Cristen: I would have said, "No. Go home."

Molly: Well, then we would have burned you as a witch. So yes, thanks to all listeners who reminded us of that. And now, I think we're going to share some theories from our listeners about what Mrs. Claus' first name is.

Cristen: Yeah. George wrote in and he pointed out that in The Autobiography of Santa Claus by Jeff Guinn, her name is Layla, Layla Claus.

Molly: Heather wrote in and said that, "If you saw the 1970 special Santa Claus is Coming to Town, then in that show, it's a girl named Jessica who saves Kris Kringle, a young, handsome red-haired Santa, from Burgermeister Meisterburger. Burgermeister is mean and cruel, and does not let children have toys. Kris, who as a human raised by elves, gives toys to all the kids and yes, a doll to Jessica. They fall in love, flee the town, get married, and grow old and happy and fat together. Kris learns his real name is Claus and becomes Santa Claus, so that makes Mrs. Claus Jessica Claus."

Cristen: Jessica Claus. We've got Layla, Jessica, and this one for Virginia will round out our trio of names and it is my favorite. I thought this was the cutest story we got. Sorry to other suggestions, but this one just takes the cake. So basically, Virginia was hanging out around Christmas with her boyfriend and his 10-year-old daughter at the time, and his daughter asked her what Mrs. Claus' first name was, and she said, "I didn't want to tell her that no one had ever thought to give Mrs. Claus her own name, so I told her that Mrs. Claus was Mary Christmas, and she decided to change her name once she married Santa.I also told her that I guess she couldn't have hyphenated her name to Mary Christmas Claus, but Santa and she had been married so long that people really didn't hyphenate names back then anyway," so I thought that was pretty adorable. And if you guys have any emails that you would like to send our way with your thoughts, feelings, and comments, send them on to MomStuff@HowStuffWorks.com, and of course during the week, you can follow us on our blog. It's HowToStuff and you can learn more about obesity and health, and the right way to assess your weight at HowStuffWorks.com.

Announcer: For more on this and thousands of other topics, visit HowStuffWorks.com. Want more How Stuff Works? Check out our blogs at the HowStuffWorks.com homepage.