WiiFit vs. WiiFat

May 22, 2008 4:42 AM

"You don't tell kids that they're overweight ... This can have such a negative effect on young girls especially, that they can focus on eating and develop eating disorders." A professor of nutrition takes on WiiFit.

At the core of the issue is the program's use of BMI as primary indicator of physical fitness. But BMI isn't entirely reliable as a benchmark; by the BMI standard, more than half the players in the NFL are obese, and according to one opinion, BMI can play a role in over-diagnosis of anorexia. Previously.

posted by jbickers (73 comments total)

"You don't tell kids that they're overweight ... This can have such a negative effect on young girls especially, that they can focus on eating and develop eating disorders."

Don't overweight kids already have an eating disorder?

Isn't this already a negative effect?

Shouldn't those kids be outside playing?
posted by three blind mice at 5:06 AM on May 22, 2008 [7 favorites]

Don't we all know by now that BMI is only vaguely useful, as a general sort of indicator? Especially as it fails to adjust for the fact that muscle weighs more than fat, so you can be a ripped gym freak & register as overweight or obese.

But yeh, it's a shiteful indicator of fitness, especially when compared with things like how quickly your heartrate drops within a minute after extreme exertion. That's fitness. BMI is only a static measure - and inaccurate, at that - of relative fatness.
posted by UbuRoivas at 5:14 AM on May 22, 2008

I thought the core of the issue was that WiiFit is laden with annoying menus and irrelevant button pressing that ruin the pleasant flow of a real workout session.
posted by seanmpuckett at 5:15 AM on May 22, 2008 [2 favorites]

Are there seriously people who don't know that BMI is not used for kids? That 'over-diagnosis of anorexia' link sounds like a scifi nightmare: people are being forcibly treated for anorexia simply because they are short! I don't believe it.

Also, the whole 'BMI doesn't mean anything!' furphy is pretty damn ridiculous - if you're so athletic that the index is not applicable to you, you probably aren't worrying about your BMI so much as your overall fitness. If you don't have any other way to measure your fitness (ie: you don't do any exercise) then a BMI over 25 is quite likely to be more related to fat than muscle.
posted by jacalata at 5:28 AM on May 22, 2008 [3 favorites]

Are there seriously people who don't know that BMI is not used for kids?

Um, yeah, there are probably a ton of them, and they're probably the exact people who will enthusiastically buy Wii Fit for their kids. Ellen is giving it away by the truckload and the guy on the Today show liked it, so it must be great, right?
posted by jbickers at 5:30 AM on May 22, 2008

if you're so athletic that the index is not applicable to you, you probably aren't worrying about your BMI so much as your overall fitness.

hey, that snark resembles me!
posted by UbuRoivas at 5:32 AM on May 22, 2008

BMI doesn't "mean nothing," but it is broken. It works better if you use the CUBE of the height, rather than the square, because we are three-dimensional.

Also, why is it okay for policymakers and doctors to say that children are obese, but not for a machine to say it to a specific child?

Also, UbuRoivas, I am now in love with the word "Shiteful."
posted by DoctorFedora at 5:32 AM on May 22, 2008 [2 favorites]

Is this the thread that gives me an excuse to talk about Wii Fit, which showed up on my front porch last night? Reactions--

--Yeah, it doesn't pull punches during the initial diagnosis. It told me that I was overweight (174 lb., 5' 9"), re-rendered my Mii with a little belly, and then suggested I set a "weight loss goal."

--Lesson learned: yoga is hard if you've never done it before. I have a feeling that learning yoga through Wii Fit might teach some bad habits.

--I don't get the hang of many of the balancing games, though I'm not a klutz--it's already made a crack at me about how it's a wonder I can walk.

--However, Table Tilt is where it's at. Sega had better bring out a balance-board-based Super Monkey Ball game.
posted by Prospero at 5:38 AM on May 22, 2008 [2 favorites]

If this "controversy" exposes BMI as the outmoded pseudo-scientific BS that it is, then I'll be happy. The simplest measurement that indicates anything about (very) general overall health is Body Fat Percentage.
posted by C.Batt at 5:39 AM on May 22, 2008

What three blind mice said. If the alternative to telling fat kids they're fat is to tell them "oh no, you're perfectly fit"...well, that doesn't seem any more helpful, does it?

As for the girls and anorexia thing: telling fat little girls they're fat (hopefully, in gentler terms) is not the root problem. The root problem is the social factors that encourage girls to obsess over their weight to an unrealistic and unhealthy degree.

Based on what I've seen of the WiiFit so far, I can't imagine how anyone could get a real workout from it, but I do think it's a great idea, and a step in the right direction. I love video games, but generally hate exercise. If exercise could be made fun, I'd be much more inclined to do it. I don't like sports, so that's out; I do like hiking, but that's not the sort of thing you can do for twenty minutes before your morning shower.

When the Wii first came out, I thought it'd be great to have a full-body controller of some kind (wouldn't have to be anything bulky and Tron-like; just enough apparatus to attach potentiometers to a few key points on the body), so your character in the game mimics your motions in the real world. To run, jump, dodge, swing a sword/baseball bat/chainsaw, you'd have to actually run, jump, dodge, and swing. Not the same as running a triathlon, perhaps, but it sounds like an awful lot of dorky fun, and certainly healthier than sitting on the couch.
posted by greenie2600 at 5:49 AM on May 22, 2008 [1 favorite]

You'd be surprised at the kind of workout you get from Wii Fit -- part of it is that you say "based on what I've seen." It's one of those things that looks a lot easier than it is to actually do it. I was surprised at how challenging a lot of the yoga was, like the Tree pose.

That said, it's actually pretty fun, and seems to mesh nicely with the Fitness Ladder from the Hacker's Diet, which is the real-life equivalent of level-grinding (up to and including level-ups every few days). Yes, I stole that notion from xkcd
posted by DoctorFedora at 5:59 AM on May 22, 2008

I don't know wii fit. I do know that wii tennis jumping around can up my heart rate, and I know that the drums on rockband can really up my heart rate.
posted by garlic at 6:05 AM on May 22, 2008

The thing about kids is that they are still growing. They are supposed to be gaining weight; they are supposed to be getting taller. And the rates for height growth and weight growth don't necessarily match up. Some kids will go through a phase when they shoot up, get real skinny, and then put on some weight; some kids will go through a phase when they gain weight, get chubby at first, and then put on a few inches vertically and balance out. I really, really don't think it's helpful for a kid to think of herself as fat when it could easily just be the natural growth of her body, especially since giving a kid a screwed-up attitude about weight and food restriction is going to stay with her for the rest of her life.

All that said, I'd be curious about trying WiiFit because I'm one of those people who has a really hard time getting off the couch.
posted by Jeanne at 6:13 AM on May 22, 2008 [1 favorite]

Unhealthy overweight is far more common than unhealthy underweight. It makes little sense to worry about the remote possibility of accidentally inspiring an unhealthily thin person to become anorexic, when the aim of the exercise is to inspire unhealthily fat people to achieve a healthy physique. Especially since healthy physiques are represented by diagrams and silhouettes etc, not just numbers. If you're an African-American with a BMI of 30 and you look like Michael Clarke Duncan and the guy in the diagram looks more like Forrest Whittaker, you're going to notice something wrong. I think the nutritionist is grossly underestimating (mentally healthy) people's ability to properly judge their own level of fitness.

BMI is flawed as an indicator of unhealthy overweight, but it is only flawed in the exceptionally muscular (and some very unusual cases). Anyone with a BMI over 26 who is not actually fat, is probably a regular gym-goer, probably a hard exerciser, is almost certain to be fully aware of the fact that they are not fat, and is probably well aware of the general flaws in BMI measurement as well.

Further, the BMI of such an person will not tend to lower with exercise, even though all of the rest of their metrics are improving. So even if they are some sort of genetic freak who grew up hauling logs on a timber farm and who's never exercised for the sake of it in their life, they are still not at any risk of any harm from being told "You're fat. Fatty-fat-fat. You have your own postcode. Your jelly rolls have jelly rolls. Now do these exercises until you lose some weight, fatty." when they actually are not fat at all.
posted by aeschenkarnos at 6:38 AM on May 22, 2008 [7 favorites]

Also, why is it okay for policymakers and doctors to say that children are obese, but not for a machine to say it to a specific child?

Basically because the machine doesn't have enough data or analytical capacity to make an accurate diagnosis (which is different from an evaluation of group data anyway), especially as it's using an algorithm that's known to be flawed.

Not to mention the fact that berating people who are trying to do something about a problem for having a problem isn't especially productive.

I haven't run across the WiiFit in person, but wasn't there a trend for a while of buying DDR pads for the purpose of home workouts? Whatever happened to that?
posted by Karmakaze at 6:43 AM on May 22, 2008 [3 favorites]

Is this the thread that gives me an excuse to talk about Wii Fit, which showed up on my front porch last night? Reactions--

I'd appreciate any and all WiiFit reviews; really curious about it, and trying to decide if I should pick it up, or if it'll just be a batch of fitness related money down the drain.
posted by inigo2 at 6:44 AM on May 22, 2008

Is there a way to turn off or neuter the BMI thing? It does seem like a mistake to have it in there, esp. for kids who are very sensitive to this sort of thing. It can call me fat all I like, but a machine that taunts image-conscious 12-yr-old kids (boys and girls) about their weight is not a great idea.
posted by Mister_A at 6:51 AM on May 22, 2008

Yeah, you know, we just got ours last night, and the first thing my kids did was bust it out and set up WiiFit profiles for themselves. I had to moderate the whole thing, because to an almost 9-year-old and a 5.5-year old, it seemed pretty harsh. My daughter was informed that she was normal, but it asked her to set a weight-loss goal, which became a "teachable moment" about what healthy feels like and the importance of eating and getting stronger, etc. etc. But the verdict on my son was that he was "obese" based on his BMI, and that became a big mess. Possibly also a teachable moment, but mostly a big mess as he cried and said he felt "teased" (probably because his sister was saying, "ha ha, you're fat and I'm normal") (sigh). And then he refused to do any of the fun stuff because, according to him, "The Wii thinks I'm fat!!!"

The thing is, though, nearly all of the Wii games are a bit judgy -- it's not like when you lose at tennis or golf or something it says, "Try again next time!" in a cheery font. It says YOU LOSE!!!, and your poor little Mii looks all dejected and defeated. That has been something we've had to manage with the kids from the beginning, especially because they are right at that sweet-spot for elementary-school age-based competitiveness and the-world-revolves-around-me sensitivity. (I know, I know, wait til they're teens...)

Anyway, my daughter ended up spending 30 minutes doing a variety of things on the WiiFit, until she got discouraged by being told she was a "couch potato" when she thought she had been doing really well. Actually, I think the last straw was when she did something that was actually pretty hard for her -- the alternating push-ups and side plank -- and was really psyched about having done it..... only to have the "trainer" say something like, "This really isn't your best thing, is it?" (Thanks, underminer!) So again I was the moderator, reminding her that the Wii is just a machine and doesn't know that she's a kid or that it was her first time trying that move.

I think if I had tried it first, before they got to it, I would have been able to frame it a little better for them before they even started, and I might have also tried to figure out if there was a way to use it without the BMI, weight, or weight-loss tracking components. In any case, I am pretty excited to try it myself. The hula-hooping looks fun, and my daughter and I did have a blast running a race together...
posted by mothershock at 6:57 AM on May 22, 2008 [26 favorites]

... I'm with Mister_A, though. I wish it had a kid setting.
posted by mothershock at 6:59 AM on May 22, 2008 [3 favorites]

If you get defensive about being told you might be overweight then you more than likely need to consider losing some weight. It's laughable that people still parse and dither over BMI. There's no such thing as a perfect metric when it comes to assessing risk for anything. BMI, along with waist circumference, is a pretty good start. The NFL quote is rich. Those guys are obese. They also happen to be incredibly muscular. The two are not mutually exclusive.

I agree you don't tell young kids they are overweight. You tell the parents. Unfortunately, telling the parents just drives them straight out of your practice. Our hospital actually opened a subsidized clinic to help entire families with holistic weight control - i.e. multidisciplinary approaches to diet, counseling, etc. The referrals would go out and people wouldn't even answer the phone. And yeah, you have to be careful to consider if a kids weight is just a phase, but when you look at two parents with BMI's over 40, and you can't remember a time when they didn't come in with bags of snacks for the other kids to consume during the visit, you can safely see where things are headed.

Wii Fit is just Camel Lights. You put your kid in front of a video game and you've got no one but yourself to blame for any downstream effects.
posted by docpops at 7:09 AM on May 22, 2008 [1 favorite]

Having received Wii Fit on Tuesday (thanks Amazon!), I find it motivational. It's motivational in the same way that Nokia Sports Tracker is. It reminds me when I'm being lazy and I can see the evidence of my effort when I'm not, even if I'm not shedding pounds like mad or getting ripped or turning into a hill climbing monster. I don't just have to think back and say "gee, I exercised a lot," I can say "I biked 35 miles last week," and "I did some light stretching and aerobics for 15 minutes yesterday." That sort of thing.

Now that I have something to remind me of my laziness, I've finally gotten around to biking a reasonable amount. Wii Fit is doing the same for other forms of exercise. And since there are fun minigames, it's something I actively want to do. Turn it on, see how much I weigh, play a minigame or two, do some "exercise" and play a couple more minigames. For a lot of people, even that small amount of effort will end up making a big difference.

What I like about Wii Fit is that it encourages me to do things I wouldn't normally do. Yoga poses, step aerobics, and fun little balance minigames. My balance sucks. I will be a better and healthier all around person for doing them for half an hour a day in addition to my cycling for an hour a day. And more flexible. God knows I need that.

And yes, it called me obese. Why? Because I am. Until a month ago I was almost entirely sedentary. I'm 5'9" and weigh around 230 according to the Wii, or 240 according to my ancient bathroom scale. (Who knows which to believe?) Either way, I am certainly obese. I know it. Telling me that doesn't make a whit of difference in my motivation. Being reminded regularly when I have failed to do what I would like to do to fix the problem? That's motivation.

Of course, I'm nearly 30, not 12, so that may make a difference. That and I long ago made peace with my body. My size has no bearing on my choice to exercise. The way I feel does.

BMI may be flawed in corner cases, but for the majority of folks, it's at least a reasonable general indicator of a healthy weight if you have nothing more to go on.

Anyway, I like Wii Fit. It's got fun minigames and reasonably good excercise. For a fatty such as myself, it's enough to at least get the heart pumping a little. Is it strenuous? Not so far, but it starts you off very easy, like 3 minutes of running in place easy or 3 minutes of step aerobics easy. The best part is it gets me doing things I don't normally do, so it exercises muscles that otherwise get little to no workout, and stretches me out, helping my flexibility and balance.

And I don't have to join a fucking gym or read a book to do it. Just do what the screen says. It's definitely better than the big fat nothing I was doing before.

On preview: God I ramble...

Also, is it really wrong of the trainer to say "you aren't doing very well" if you're not? Maybe it's just me, but shouldn't kids learn that sometimes their best isn't really very good and only through practice will they get good at something? I thought he was pretty nice when I had to step off the balance board for a breather when I was doing the tree pose and he said "I know you took a break in the middle, maybe you can try harder next time."

Yes, I sucked it up. I deserve that. Maybe next time I'll be able to do better.
posted by wierdo at 7:15 AM on May 22, 2008 [5 favorites]

Are there seriously people who don't know that BMI is not used for kids?

Those idiots at the CDC.

Morans at the American Association of Pediatrics

&c, and so on.
posted by a robot made out of meat at 7:21 AM on May 22, 2008

...I'd appreciate any and all WiiFit reviews; really curious about it, and trying to decide if I should pick it up, or if it'll just be a batch of fitness related money down the drain.

The jury's still out for me on how good it is as a fitness tool. Karmakaze mentioned Dance Dance Revolution above--I've played at home for a few years now (and can play better than most people), and while 30 minutes of expert-level DDR can be a serious aerobic workout, 30 minutes of Wii Fit didn't make me break a sweat. Part of that is because you spend down time navigating menus in between exercises. I've spent more time on balancing games than anything else, and I haven't unlocked all the exercises, so my first impression could be wrong.

I will say that my upper arms and shoulders are slightly sore this morning. The exercises can be harder than the game lets on--for example, the pushups/side-planks exercise requires you to place your hands on the balance board, and with that distance between your hands you may as well be doing diamond pushups. I can usually manage at least twenty normal pushups before the point of failure, but six Wii Fit pushups and side planks were quite difficult for me. (Keep in mind that the game is measuring your balance the whole time you're doing this, and that it gives you a grade afterward. I haven't gotten a grade on my balance above "amateur," and it was happy to call me "unbalanced" a few times.)
posted by Prospero at 7:23 AM on May 22, 2008

Nearly all of the Wii games are a bit judgy

I wonder if something isn't being lost in translation from the original Japanese. We got our Wii Fit yesterday and I noticed a lot of subtle "Japanese" gestures. I also feel that the Japanese sometimes don't soften the blow when it comes to telling someone they are fat. I remember being shocked at first when I observed (or experienced myself) this behavior.

As far as the win-lose thing in this and other Wii games, even at such simple games like Rock-Paper-Scissors, the loser will often shout "maketta!" which means "I lose." But typically it's followed up with a "ganbarimasu!" which roughly translates to "next time, I'll do my best!"

Not only did I test out as "overweight" (I blame my Eastern European bone structure), but I also was about 10 years older, and my Mii did the amusing bent-over-and-smack-my-back-like-I've-been-in-the-rice-field-too-long gesture.
posted by ikahime at 7:31 AM on May 22, 2008 [3 favorites]

a robot made out of meat : both those links refer to using the BMI as a way to rank kids against the population of their age-mates, and say that kids at extreme edges of the ranking probably need attention. Neither of them suggest that the BMI itself can be used to rank a kids relative fatness, as it is for adults (essentially because the BMI cutoffs are giving an adults position in a ranking relative to other adults, and as mentioned above, kids have different height/weight ratios to adults).
posted by jacalata at 7:31 AM on May 22, 2008

I'm onto day 14 of Wii Fit, having picked it up on the weekend after the Australian release. I've used it every day for at least a half hour of exercise time. On top of that I've been swimming for about an hour twice a week. Diet wise, I haven't changed much. I set my goal at 5kg, to get me into the ideal BMI range. So far I've only lost 0.3kg, so it certainly isn't a magic bullet.

I have been focusing mainly on the yoga and muscle exercises in my daily workout, which I do first thing in the morning. As others have said, the yoga exercises are harder than you expect and you do work up a sweat. I can feel that I'm getting better at most of the exercises and my muscles get tired, so forgetting about BMI I think it must be doing some good.

Overall, I'm pretty happy with it and I think it is worth the money, even if we are ripped off compared with the US.
posted by CaveFrog at 7:34 AM on May 22, 2008

Some other random observations
- The initial test results were pretty brutal, telling me I was overweight and probably tripped over my own feet. As an adult I can cope with that, but I can understand kids being freaked out by it.
- In my morning workout, I'm getting a bit bored with the repeated fitness tips between exercises and the mashing of the A key to get through them.
- The "Wii Fit Age" which is based on real age, BMI and balance tests is very variable. So far it has told me I'm everything from 26 to 44 when my real age is in the middle. I had a friend that was told on the initial test that she was 65, which is more than double her real age. This put her off to the point of not wanting to use it any more.
- I find it quite useful just as a way of tracking weight and exercise over time. Exercise that you do outside of Wii Fit can be recorded manually.
- It took me just over a week to open up all the exercises and games. I think long term I would like to see some more activities added for some more variety. Maybe this can be done via WiiWare.
posted by CaveFrog at 7:40 AM on May 22, 2008

jacalata: that's kind of the same thing. The adult cutoffs came from population data also. I don't know if wii fit asks your age/sex and pulls out the age-sex-matched distribution for kids, but it would be easy to do. Instead of just saying "Your BMI is X, you're probably overweight" it should say "Your BMI is higher than 97% of kids your age and sex; you're probably overweight."
posted by a robot made out of meat at 7:41 AM on May 22, 2008

docpops: The NFL quote is rich. Those guys are obese. They also happen to be incredibly muscular.

come again?
posted by crunch buttsteak at 8:04 AM on May 22, 2008

docpops, my but you are judgmental. This is a video game that can only be played by getting off the couch and being active. I suspect many parents of already-active kids are buying this as another way to help ensure that their kids stay active. On the flip side, there are probably many parents who are buying this to try to spark an initial interest and enthusiasm in physical activity among indolent kids. Do you think that a 12-yr-old kid with a BMI of 35 is going to go out for the soccer team? Of course not. This WiiFit could have been (and could still be) a useful tool for some parents and some children. Wouldn't you say that some exercise is better than none?

Our fictional obese 12-yr-old friend here needs more than just moderate exercise; he also needs sane dietary counseling; most likely his whole family does. But moderate exercise is a great place to start, and the living room is a safe place to start it (for many values of the word safe), and the videogame interface is one with which most 12-yr-olds in the US and other developed countries are familiar. It's not a cure-all, and it's not the end of the problem, but it might be the start of the end for some kids with weight problems, so why not give it a try?
posted by Mister_A at 8:05 AM on May 22, 2008 [1 favorite]

Oh, and another thing - you can't always lay blame for everything kids do at the parents' feet. I have friends who compete in triathlons and have been active their entire lives; their 13-yr-old daughter has absolutely no interest whatsoever in any sort of physical activity. Anecdata for sure, but the world's a rich tapestry and all.
posted by Mister_A at 8:07 AM on May 22, 2008

Mister_A, I'm sorry you feel it's judgemental. I guess it is. I'm considering the absurdity of purchasing a video game as a means of stimulating a child's interest in exercise and finding myself incredulous. I don't doubt that there may be a short term stimulus as far as activity, but I think people delude themselves if they imagine that their child's weight problem will be assisted by television, even if they happen to be jumping around in front of it while they watch.

As for parents whose kids aren't active when they themselves are, so be it. All we ever tell parents is set good examples - in all likelihood when those kids get to a point where there is some appealing motivation to be active, it's the memory of their parents that will bring them to it.
posted by docpops at 8:18 AM on May 22, 2008

First of all, calling a kid fat is terrible. The term has absolutely no specific technical meaning, conveys no information, and worse is routinely used as a perjorative relating to appearance only, not health.

The term "fat" is like the terms "ugly" or "stupid". How about I pass around some Math and Physics tests of my own design, and if you don't get the minimum number of questions right, I grade you as "stupid"?

The term is either "overweight" or "obese". Overweight is better because it clearly indicates to the kid that there is an objectively determinable target weight for them that they are already over. More importantly, the target weight is not a function of appearance. Finally, I find it laughable that a game made in Japan renders your character as fat or not based on your BMI. Ha ha fat Americans, we get it. Look at this fat bastard, a BMI of 30! Or this one, with a BMI of 39! Fatty fatty fat fat.

The further problem is that it actually isn't the kids fault if he's fat. Kids do not determine their own diet, and their activity level is often determined by what is left after school and homework.

The other problem is that the fitness industry in the U.S. rivals palmistry and astrology in its total disdain of science. Let's say there's a 14 yr old kid who needs to lose 60 pounds. He's committed. What should he do, precisely? He walks into the bookstore and is presented with a billion fad workouts, which should he pick? Should he weightlift? Do cardio? A mix? What's the mix? How are you calculating it?

Someone linked that gyminee.com site a few days ago. What an awful fucking mess. Anybody can make a workout plan, and the most popular ones are either associated with some well-established brand, i.e. Men's Health magazine, or have a stunning picture of some hardbody next to the workout.

How are people designing these workouts? On the basis of what they heard in football camp or in track 20 years ago? Would you go to a doctor if his knowledge of medicine went no further than what he learned in medical school 20 years ago? Atkins diet vs. calorie restriction diet, vs blah blah blah.

If the neophyte cannot get reliable information on how to start and how to progress that he can rely on as correct, he won't start. The problem lies with so-called experts who can't get their stories straight, not with confused kids.
posted by Pastabagel at 8:24 AM on May 22, 2008 [3 favorites]

Infamous NFL fattie Justin Tuck (BMI 32.5). Tuck is the football gentleman on the left, shown here badly frightening another gentleman.
posted by Mister_A at 8:44 AM on May 22, 2008 [1 favorite]

This repeated point needs repeating -- BMI-based judgments completely and utterly fail our muscled Athenian youth.

Well done.
posted by Durn Bronzefist at 9:03 AM on May 22, 2008 [10 favorites]

Are kids these days really not used to being challenged at all, and are conditioned to give up if they get a negative response? It's an exercise program, but it's also a video game. When I was young, you didn't get unlimited lives and the ability to retry like you do on these newfangled Mario-type games. You took your three lives, you earned some more if you could, and when they were all gone you chucked the controller across the room only to return a little later. Because that little demon inside the machine was challenging you to come back, and do better.

I remember in elementary school, our P.E. teacher, a sweet guy, great with kids, who retired when I was probably in fourth grade, regularly played this record as a warm-up workout for the class. Yeah, it was pretty dated by that point, but in its silly ridicule, it was challenging, too. A little borderline-negative feedback might burn a little, but if you give up when someone says something slightly negative, you're going to have a hell of a time with a lot of the world.

I'm looking forward to playing WiiFit this weekend, since it looks like the weather might not cooperate with my holiday plans the whole time. And if that jerk of a game tells me I'm doing it wrong, I'll be back later to prove it wrong. (Well, assuming I like the game and my girlfriend lets me come over to play it.)
posted by mikeh at 9:10 AM on May 22, 2008

BMI doesn't "mean nothing," but it is broken. It works better if you use the CUBE of the height, rather than the square, because we are three-dimensional.

That's the dumbest thing I've ever heard. Does it also not work because we're not square?
posted by electroboy at 9:11 AM on May 22, 2008

Hey, folks! I was a totally obese 12 year-old. Well... I was a totally obese kid from grade 8 to about age 15. But 12 is the age I remember the best: when I was 12, I weight 180 pounds.

The thing is, when you are a totally obese 12 year-old, you don't need to be told. You know. Every single day, every single event of your life revolves around the fact that you take up more space than you're supposed to. Every single meal is punctuated by the fact that you, being totally obese, got there by eating more than others. Every single trip to buy clothing is horrifying and painful -- you don't get to wear kids clothing because it doesn't fit. Nothing sucks more than being suggested, when just a kid, that perhaps you should check out maternity wear because it might fit better. Every time you meet a stranger, you know they are judging you. You are too big, and the whole world knows it, and you know the world knows.

I was totally obese because I ate too much. I ate too much because I was unhappy, extremely unhappy. I didn't understand this at the time. I knew I ate too much, but I didn't understand that my constant desire to eat sweet things was an obsession of sorts. I knew that I shouldn't want to eat so much, but I wasn't even able to understand that the root cause was unhappiness. It wasn't until years later that I could understand how unhappy that period of my life was. I was living inside the fog at that time, so I couldn't see it myself. I knew I was supposed to diet -- oh, my mom tried everything to help me find a diet that could work--but I didn't understand any of the psychological issues that relate to being totally obese or getting out of that stage.

I know, boohoo. Poor me. Anyway, I say all this to explain the following: I know what it's like to be a totally obese 12 year-old, and I can tell you that telling a totally obese 12 year-old she's fat totally does not improve her life.

It was 7th or 8th grade when the concept of "obese" was first introduced to me. The P.E. teacher had charts set up, with explanations. None of us were told to find ourselves on the charts, but I'm sure everyone did independently. So, I took my weight, looked at the chart, and realized I counted as "obese." I had definitely known that I was overweight, but now there was a title for me. There was a word that described me, and if you think a 12 year-old can distinguish between a title for her temporary condition and herself, you're wrong. Or, at least, I (and I'm a smart cookie, I swear!) couldn't. That was me the word was describing--I was obese, and that clearly had something to do with my core value as a human being. I felt even less motivation to try to lose weight at that point because I was obese, and I should just get used to it instead of constantly denying it. Man, that sucked.

Kids have to know that they're overweight, when they're overweight. But, even more importantly, they have to be given the appropriate tools to handle that condition. Saying that there's no problem just telling a kid the facts about their condition because maybe that'll actually get them off their fat asses and outside playing... Well, that's a little blind. It's a little cruel. And it's counter-productive.
posted by Ms. Saint at 9:12 AM on May 22, 2008 [12 favorites]

Someone linked that gyminee.com site a few days ago. What an awful fucking mess. Anybody can make a workout plan, and the most popular ones are either associated with some well-established brand, i.e. Men's Health magazine, or have a stunning picture of some hardbody next to the workout.

(Ahem) Guilty as charged. But those are apples and oranges, because we're talking about two very different things here: motivation and education. Gyminee, in my view, is more about motivation than anything else - it seems like most of the people who use such a tool have some knowledge of fitness, and it is designed as such (you have to know what a tricep or a quad is, for instance, in order to know to browse to the videos targeting those areas).

Wii Fit, on the other hand, would seem to be as much about education as motivation - "Hey kids, look at this cool activity you can do - it's a game, no really, it's a game!"

But that's where the difference starts to emerge, because the guy who knows he needs to workout, when yelled at by a drill sergeant saying "Move it, fatty!", will take it and use it to fuel his fire. The kid encountering these concepts for the first time, however, is more likely to head back to the couch and to Mario Galaxy, which doesn't berate him but in fact rewards him for sitting there, staring at the screen for hours.

In a perfect world, mom and dad would be standing by to help coach the kid. But in a perfect world, the kid wouldn't have gotten so big in the first place.
posted by jbickers at 9:14 AM on May 22, 2008 [1 favorite]

If you're an African-American with a BMI of 30 and you look like Michael Clarke Duncan and the guy in the diagram looks more like Forrest Whittaker, you're going to notice something wrong.

Especially if you're female.
posted by grubi at 9:14 AM on May 22, 2008 [1 favorite]

(There are some errors in what I said. First off, I meant "weighed" at that one point where I said "weight." Second, I don't know why I said "grade 8 to age 15." That should be "age 8 to 15." Huh.)
posted by Ms. Saint at 9:20 AM on May 22, 2008

Not to beat a fat dead horse, but the BMI is a pretty poor tool. I am 6'0" and 190 pounds, very little belly and good musculature. I had 11 percent body fat last measurement, which is decent for a 47-year-old, I'm told. My new job's insurance relies solely on BMI for determining health risk. BMI indicates I am overweight at 26, and I will get hammered in my co-payment obligation.
posted by bigskyguy at 9:21 AM on May 22, 2008

more than half the players in the NFL are obese

They aren't? Do they wear fat suits for the Big Game?
posted by Blazecock Pileon at 9:27 AM on May 22, 2008

Sure, there are some fat guys in the NFL, but the point is that there are also a lot of big, lean, muscular guys who are "obese" according to a stupid chart. Look at the BMIs of these NFL running backs. The only one who is kinda fat on the list is Jerome Bettis.
posted by Mister_A at 9:45 AM on May 22, 2008

I was a fat kid, kinda. The truth is that I wasn't really - it's just that I grew wide before I grew tall. In 6th grade my head was almost perfectly round, as wide as it was tall (in retrospect I looked a little like Hiro Nakamura). I hated myself, but I also grew out of it to a certain extent. My parents made me exercise and eat fairly well, and that was that.

As far as videogames helping with fitness, I don't know anything about WiiFit. What I can tell you is that by playing an hour or so of Dance Dance Revolution a day for a few months last summer and eating more healthily, I trimmed down pretty nicely. Didn't get freaky thin, didn't get super athletic, but did lose about 10 or 15 pounds and got a bit more aerobic. I'd actually avoided DDR for a long time before that, because I always associated it with the weird kids from high school, but it turns out htat it's actually a really fun way to get in a bit of shape.
posted by OverlappingElvis at 9:58 AM on May 22, 2008

there are also a lot of big, lean, muscular guys who are "obese" according to a stupid chart. Look at the BMIs of these NFL running backs.

Newtonian physics is stupid. Just look at the Lorentz contraction of these objects moving close to the speed of light.
posted by Durn Bronzefist at 10:12 AM on May 22, 2008 [5 favorites]

I can't really think of any 'flaw' that it's helpful to have pushed in your face, especially in the very moment you're trying to address it.

Like say you *finally* respond to that e-mail from your close friend that you've been meaning to get to, because really, you want to be in better touch with your friends.

Your email system: "You're a bad friend!"

Say you have anger issues, and you're about to sit down with friend to try discuss something that's getting under your skin in a calm and non-agressive way.

Your friend: "You're a hysterical tantrum thrower!"

I observe 'flaws' in people all the time, many muce more serious than overweight. But I hardly ever tell them because either they know and are working on it and getting flack from me won't help, or they know and don't care, so what's the point, or they don't know, but probably won't accept it from me anyway.

So I don't understand the people defending this. Even if you think it's not actually *harmful* for a machine that kids want to use for fun and to get exercise to tell kids they're fat (and I think you're wrong) - what good can it possibly do?
posted by Salamandrous at 10:15 AM on May 22, 2008

Are kids these days really not used to being challenged at all, and are conditioned to give up if they get a negative response?

I don't think anyone's saying that. But I will say that it helps to know your kid in terms of dealing with this stuff. My super-sensitive, perfectionistic 9-year-old will take a negative response deeply personally; her best friend will shrug it off. (As for myself at 9, the "not good enough" response made me work harder, but in the long run that's just something I ended up needing to sort out in therapy...)

For really little kids, they need to feel good about trying something challenging the first time -- you can get to the serious critiques later. When I taught kids piano, it was all about gauging their abilities and giving them interesting/challenging but *accomplishable* tasks at the start. Once they'd built up some confidence, they had a kind of bank to draw from when they tackled the harder things and didn't get it right the first time (or the first 50 times).

I just tried the WiiFit myself, and I have to say, I actually thought it might be more fun if you could choose the personality of your trainer -- it's Jackie from that Bravo show! or the mean one from the Biggest Loser! -- or have a Mario character (like Bowser or Princess Peach, ha ha) train you or something. Just to mix it up a little.
posted by mothershock at 10:15 AM on May 22, 2008

I don't think there is an epidemic of people feeling just right the way they are when they shouldn't. I think the wii can tell you how much you weigh ask you if you want to set a weight loss target based on that and let you be on your way. I think that would be a better way to do things. I'm not offended and it wouldn't keep me from buying the game for my kid even if I had an overweight kid. What it comes down to for me is the simple fact that it would be obviously better if they didn't call people overweight, it isn't something that many people are going to benefit from being told and it is something that could bother people. Probably a clash of cultures!
posted by I Foody at 10:23 AM on May 22, 2008

That's a good idea, mothershock. I don't really see why it shouldn't have feedback options the way games have difficulty options. Those who want it easy will play it on easy (or "gentle") regardless, and there's always the subtle irritation of knowing you're playing on "easy" to get you to try the next level. Or with your suggestion, the harder trainer. I'm kinda surprised it doesn't have something like that.

But culture clash, yeah. I still remember telling a Japanese teacher I worked with awhile back "Oh, good class. Your kids are really smart!" and being told somberly "No, no. They are below average." Maybe we could use a bit more honesty, but more flies with honey, etc, etc..
posted by Durn Bronzefist at 10:26 AM on May 22, 2008

Unhealthy overweight is far more common than unhealthy underweight. It makes little sense to worry about the remote possibility of accidentally inspiring an unhealthily thin person to become anorexic, when the aim of the exercise is to inspire unhealthily fat people to achieve a healthy physique.

I don't think that most anorexics start out unhealthily thin. I think a lot of them start out like I did: slightly chubby. So you're a slightly chubby 13-year-old, and that's kind of awful. You get teased or you're invisible, and 13-year-old girls are miserable and take everything way too seriously anyway. You lose ten pounds, and all of a sudden you're a rock star. You get tons of positive attention. Cool, popular girls want to talk to you about your diet. So you lose ten more pounds, and even though your parents are a little concerned, you're still a rock star. Now the cool, popular girls want you to sit at their lunch table so they can emulate your (not) eating habits. So you lose ten more pounds, and nobody thinks you look good, but at that point you can't stop. Being thin is your entire identity, and dieting is all you think about all day. You can't stop dieting without losing your entire sense of self.

I don't think there's any contradiction between preventing eating disorders and encouraging healthy eating and exercise habits. The same strategies work for both. Teaching chubby little girls to hate their bodies doesn't promote fitness, and it does promote eating disorders. What works is encouraging chubby little girls to eat well and exercise because it's healthy, enjoyable, and will make them feel good, and also teaching them that the way they look is not the sum total of their value as a human being. It is also good to encourage kids to pursue fun, positive activities that will give them an identity that isn't based on how they look.

Wiifit sounds like it could be fine if it did away with the negative tone, but personally I'd be more in favor of coming up with more fun, non-competitive opportunities for kids to engage in physical activity. There are a lot of kids who don't like competitive sports or ballet class but who might enjoy hiking, riding a bike to school, dancing like a dancing fiend, playing tag, walking to the store with some friends and hanging out and talking while you walked, gardening... lots of fun physical activities that feel like having fun, not like taking your exercise medicine. Kids don't seem to have a lot of opportunities to engage in those fun physical activities these days, and I think it would be good to figure out ways to reintroduce them.
posted by craichead at 10:27 AM on May 22, 2008 [2 favorites]

I hope I'm not jinxing it, but I am really impressed with the way everyone has handled this hot-button issue in this thread. While I don't agree with every viewpoint presented, I thank you all for presenting them in a respectful and constructive manner.
posted by Mister_A at 10:33 AM on May 22, 2008

The simplest measurement that indicates anything about (very) general overall health is Body Fat Percentage.

Where in the hell did you learn this? Body fat %age says nothing at all about "general overall health." It's completely possible to have good metabolic fitness and be fat. All body fat %age tells you is how fat you are, which has little to do with "health."

Get a "simple" blood test and blood pressure reading to find out if you have metabolic syndrome- that's the simplest measurement of overall health. And if you have it, a little exercise that will NOT pretty you up or make you lose much weight will save your life.

The obesity myth is more than alive and well- it's making intelligent people say very stupid things. We should try to be non-sedentary. Everything beyond that is gravy and will not save your life.
posted by ethnomethodologist at 12:09 PM on May 22, 2008 [1 favorite]

I think there is a lot lost in the cultural translation here. This is a system developed in Japan by Japanese people and it is likely that not much was changed for the American release. From my experience living there, Japan seems to be the one place more diet and weight obsessed than the United States, especially among women. Most of my female friends watched their weight or skipped meals, all of the Subway restaurants in Nagoya had the word 'DIET!' emblazoned on their doors, and if you're overweight fuggetabout buying clothes at Parco or any of the trendy department stores. Plus, while Japanese people have this reputation for being indirect about most things, they are surprisingly direct about peoples' age and weight. My poor husband who isn't even overweight would frequently get patted on the belly and casually called a fatty.

Of course, not having a specialized BMI for the young ones is not the way to go. It's something that would be a really easy fix and I'm surprised that they didn't think about it.
posted by Alison at 12:18 PM on May 22, 2008

But culture clash, yeah. I still remember telling a Japanese teacher I worked with awhile back "Oh, good class. Your kids are really smart!" and being told somberly "No, no. They are below average." Maybe we could use a bit more honesty, but more flies with honey, etc, etc..

That's not necessarily honesty -- in Japan it is considered polite to play down compliments. Those kids could be in the 98th percentile, and you'd still hear, "oh, not really, it's nothing special", etc. Which isn't to say that the kids couldn't actually be below average, but if that teacher was from Japan, I suspect he or she was just trying to deflect the praise a bit.
posted by vorfeed at 12:23 PM on May 22, 2008

Alison, little ones come in many shapes and sizes, and develop at different rates. Attempts to generalize kids' health based on such simple anthropometric data are most likely doomed to failure.

However, there are interesting anthropometric data that can supplement and even potentially supplant the BMI measurement. Waist:hip ratio, waist:height ratio, waist circumference, and hip circumference are additional anthropometrics that may provide more valuable health information. Here is a summary of a paper from Lancet, provided by American Family Physician, that suggests that W:H ratio and waist circumference are predictive of cardiovascular disease.
posted by Mister_A at 12:31 PM on May 22, 2008

jbickers, I didn't mean to call you out, and if you already know what you are doing, I can see that gyminee would be very useful for tracking your progress and sharing that progress with others as a way to motivate you further.

My point is that there seems to be no unbiased source of fitness info that's scientifically based, that assumes the kid knows nothing, and tells them what to do the moment they step into a gym or what things to do if they want to workout from home. The only site I've found that's of any use in that regard is ExRx.net, and even that presumes a level of knowledge above that of a beginner.
posted by Pastabagel at 12:34 PM on May 22, 2008

Alison, little ones come in many shapes and sizes, and develop at different rates. Attempts to generalize kids' health based on such simple anthropometric data are most likely doomed to failure.

True, but applying adult BMI indexes to kids is a terrible idea, especially when there are special indices for children and teens.

Still, an even better idea would be the ability to turn the BMI feature off. There are a lot of people who could benefit from the system who would be turned off by the negative feedback. I always turn off the feedback voice on DDR just because I don't need to be electronically mocked when I screw up, and also because that guy is really annoying.
posted by Alison at 12:47 PM on May 22, 2008

I'm considering the absurdity of purchasing a video game as a means of stimulating a child's interest in exercise and finding myself incredulous. I don't doubt that there may be a short term stimulus as far as activity, but I think people delude themselves if they imagine that their child's weight problem will be assisted by television, even if they happen to be jumping around in front of it while they watch.

Do you have any familiarity with Wii Fit at all? Or with Wii, even? I mean, could you describe how one uses the thing in your own words?

Personally, I thought that having a ball thrown at me repeatedly and then running in circles was a ludicrous way to stimulate my interest in exercise, but I don't think that everyone who enjoys playing competitive sports is delusional.
posted by desuetude at 1:23 PM on May 22, 2008

--However, Table Tilt is where it's at. Sega had better bring out a balance-board-based Super Monkey Ball game.

Oh my god. How awesome would that be? Also: SSX.
posted by Miles Long at 1:24 PM on May 22, 2008

My point is that there seems to be no unbiased source of fitness info that's scientifically based, that assumes the kid knows nothing, and tells them what to do the moment they step into a gym or what things to do if they want to workout from home.

100% agree with you - and this is precisely why the Wii Fit thing might be such a negative, because countless parents that don't really investigate things deeply will see Ellen handing out 200 Wii Fits on her show, or will see Matt Lauer extolling the virtues of this new miracle device, and they'll say "Oh, my overweight kid loves video games - I'll get them this thing! The man on the TV says it'll help him get in shape!" So it becomes yet another form of misinformation (especially given the fact that the tracking system is largely based on BMI). More's the damage, then, when said kid gets called a fatty by his beloved Nintendo.

Actually, there is an "unbiased source of fitness info that's scientifically based, that assumes the kid knows nothing, and tells them what to do" - it's called gym class. But for whatever reason(s), that doesn't seem to work anymore.
posted by jbickers at 1:46 PM on May 22, 2008 [1 favorite]

Rereading my previous comment, I think I came across like I was endorsing outright criticism or abrasive comments inside the game. That's not what I really wanted to say. I think that, in spite of some negativity that the game conveys, which is kind of in line with their previous Wii games that have the "You Lose!" mentality that are more in line with Japanese culture than Western culture (which I think is probably much more of a negative than a culturally-neutral point), this is still going to be pretty fun for kids.

But is Wii Fit really targeted at kids? Like Brain Age, which is fairly popular among even older adults, I think the target audience for WiiFit is probably over 20 years old. The people who were rushing out to get it on Wednesday morning in my area were probably more indicative of those who are buying it for kids (men in their 40s/50s, a soccer mom-type) but I think overall it's going to be more of a hit in adults. Of the five people interviewed for the NY Times, the youngest was 18 years old.
posted by mikeh at 1:48 PM on May 22, 2008

After playing with the balance board a bit more today--this is an amazing piece of tech.

After playing Wii Fit for long enough you'll be invited to take the Ultimate Balance Test. Basically, you have to distribute your weight on the board evenly (50% on the left foot, 50% on the right) and hold the position for three seconds. Each round has a decreasing margin of error, and the margin of error for the third and final round is a measly .1%.

I thought it was one of the most ridiculous challenges I'd ever come across in a video game, until I realized that in order to beat it you have to hold your breath on the final round. That's how precise the balance board is.
posted by Prospero at 2:02 PM on May 22, 2008 [1 favorite]

I don't like the idea of kids being encouraged to obsess over their weight, and even the idea of basically healthy kids using any kind of product specifically labelled as being for health/fitness bothers me.

However, I can't believe people are criticising Wii Fit (clue: it has FIT in the title) for measuring weight and pointing out when you screw up. How can you have any kind of challenge or interactivity without goals and success/failure? You can't always allow for bad parents and ludicrously-sensitive people.

And BMI clearly isn't an all-encompassing measure of fitness, as it can label musclebound athletes (not quite Wii Fit target audience, right?) as obese and couch potatoes like me as optimal, but so what? It's a reasonable indicator based on easily-obtainable data, and you don't have to weigh in again after the initial set-up.

(The worst thing about it is definitely the menu overload; they could've easily cut out half of the menus and button presses)
posted by malevolent at 2:11 PM on May 22, 2008 [1 favorite]

That's not necessarily honesty -- in Japan it is considered polite to play down compliments.

I wasn't complimenting the teacher, but their class. This might seem much the same, as the teacher may take some degree of credit for it, but they never failed to beam and discuss their class scores if they actually were a top class. OTOH, if I said: "You worked very hard today" then of course they would say "No, no. Not me."

Now the "below average" comment was directed to me, not the class, but I got the distinct impression that she never let her class forget that they were below average, either.
posted by Durn Bronzefist at 2:13 PM on May 22, 2008

First of all, calling a kid fat is terrible...The term is either "overweight" or "obese".

and it is likely that not much was changed for the American release.

Actually this was one of the things changed for the American release. It uses the terms "Overwieght" and "Obese" not "Fat". Also I believe the board was made a bit sturdier, as the average American is larger than the average Japanese. The weight now allows up to 330 lbs and can take up to 600lbs of force. Double what it used to, in case people decide to jump on it.
posted by P.o.B. at 2:52 PM on May 22, 2008

Super Monkey Ball... SSX...

I've always thought the way to get people to exercise is to make it incidental to the activity. When I was little, I'd run for miles chasing a silly soccer ball, but hated just running for the sake of running.

Imagine World of Warcraft where you actually have to walk (or, if you need to move fast, run!) everywhere...
posted by LordSludge at 5:28 PM on May 22, 2008

Morans! (thank you for the smile)
posted by mrgrimm at 5:36 PM on May 22, 2008

Imagine World of Warcraft where you actually have to walk (or, if you need to move fast, run!) everywhere...

LordSludge, check this out, and scroll down about 3/4 of the way to "Ultima 7 with Exult and Dance Pad." I don't see why this same thing couldn't be done with any number of games.
posted by jbickers at 2:50 AM on May 23, 2008

If this "controversy" exposes BMI as the outmoded pseudo-scientific BS that it is, then I'll be happy.

Quoted for mutual support of that faint hope.

electroboy sez: Objecting to BMI because it's scaled only by the square of height is the dumbest thing I've ever heard. Does [BMI] also not work because we're not square?

Given the choice between assuming you're trolling and assuming that you really, really didn't understand the first thing about this criticism, I'm going to be the dork who assumes the misunderstanding and explains the whole thing in agonizing detail. Here goes:

Let's imagine we want to create a number that will describe a person's build. We might start by just asking how much fat they have. But people don't just come in different fatness levels, they come in different overall sizes, and we want our measurement to make up for that. Ideally, our measure will give us pretty much the same number for a person who's fit but really tiny as it will give us for a person who's fit but really large. Or if both people are overweight, or both underweight, or whatever—the size of their frame shouldn't matter, only the relative amount of fat they're carrying on it.

OK. When we say 'relative' anything, that always means we need to use some kind of ratio: We're going to measure the fat that they're packing in terms of their size, and the way you do that is you take some number that represents their fat, and divide it by some number that represents their size. If we pick those numbers right, then when we go from our tiny person to our large one (but same fitness, remember), they will both grow by the same amount—half again as big, or twice as big, or whatever—and when we do the division the factors that are the same will cancel each other out, and the final result will be the same.

So we're going to use their weight as an estimate of their fat. How are we going to measure their size? Just their height? Let's see if changing those the same way gives us two people with the same build. Take someone who's five feet tall and 110 pounds. Now we'll find someone who's six feet tall. That is, 1.2 times as tall. Changing the weight by the same factor gives us 132 pounds. So how are we doing? Is five-foot, 110 the same build as six-foot, 132? Not really. For some reason we didn't increase the weight enough.

Well, let's take it the other way. What is a reasonable weight for the six-footer? Say, 190 pounds. We take 190 pounds back down to 110; 110 is 0.58 of 190, so do the same change to the height. But 0.58 of six feet is only about three-foot-five. Plainly, we did not pick the right measurements for our ratio here.

OK, so, thought experiment. Let's imagine that we can take someone and just scale them up exactly to another size: Same shape, same proportions, same fitness, just a different size. We'll scale up the five-footer to six feet, that's our old 1.2 again. But to keep the same build, we also have to multiply the width from left to right by 1.2, and the width from front to back. So our person is taking up (1.2 * 1.2 * 1.2) times as much space as before. But that space should be filled with bone, organs, muscle, and fat in just the same proportions as before. So each of those components is (1.2 * 1.2 * 1.2) times bulkier than before, and therefore it's (1.2 * 1.2 * 1.2) times heavier than before, and therefore the whole person now weighs 110 lbs. * (1.2 * 1.2 * 1.2), or 190 pounds (yes, I cheated and calculated that in advance).

So aha! What we have here is a way to take a standard, fit build, and scale it to any height, and say how much an imaginary person that height, with fit that build, would weigh. And then we can weigh a real person who is that height. Divide the real weight by the calculated fit weight, and you've got a number that describes their build, which is what we wanted.

If the person is fit, the numbers are the same. If the real weight is bigger, since you set the heights equal, it means the real one is bigger than the imaginary one in some other dimension, i.e., in width. Or maybe it means that they're the same shape, but big parts of the real person are made of something that fits in the same space as fat but weighs more—like muscle. So it's not a perfect measurement; it doesn't apply to extremely muscley people. And it doesn't apply to children, since a fit child is not proportioned like a fit adult. And really, you need different standard builds for men and women, since a healthy woman has more fat than a comparably healthy man. But take care of all of that, and you've got an honest measurement of build that's independent of body size.

So what's the difference between this honest measurement and BMI? Well, in the honest one, when you're scaling that imaginary person up or down to the real person's height, you scale them in all three dimensions, so that they still have the same standard, fit build. Mathematically, the imaginary person's weight is the cube of their height (times some constant conversion factor), so the measurement of build is real weight over cube of height (again, times a constant conversion factor if you want it). In BMI, we only have weight over square of height. Which means when we change the height of the imaginary person, one of their widths changes too, but the other one doesn't. Maybe they grow a butt and a belly, but mysteriously don't get any wider left-to-right; or maybe, weirder, they get wider left-to-right but retain their flatter curves front to back. Those two are equivalent as far as the numbers are concerned. Point is, we're not really keeping the same build on our imaginary person any more, are we?

A more abstract way of putting that is to say that the square makes BMI a two-dimensional model, but bodies are three-dimensional, so it's guaranteed to be a lousy model from the get-go. Which brings us back the statement you objected to. Add in those important reservations about muscles, and genders, and children, which users of BMI ignore as often as heed, and we're all the way back to condemning it as a perfectly rubbish way to describe fitness.
posted by eritain at 3:09 PM on May 23, 2008 [1 favorite]

with fit that build -> with that fit build
posted by eritain at 3:13 PM on May 23, 2008

eritain: Do you think BMI got pulled out of air? Tall people (or for that matter other large organisms) do not actually scale their weight as the cube of height. The biological rationale is that since bone strength (hence the supportable weight) is proportional to the cross-sectional area, you don't just scale up the same organism; it would rapidly fail. BMI was originally developed as a statistical measure; it is weight*height^n to get a measure that is uncorrelated with height. The closest integer is 2; the best fit value is more like 2.3, but people couldn't do number^2.3 easily before pocket calculators.
posted by a robot made out of meat at 4:28 PM on May 23, 2008

To show that I'm not just being a dismissive internet jerk, these are three plots from a cohort that I happen to have data handy on.

height vs height/weight
height vs height/weight^2
height vs height/weight^3

As you can see, height/weight is biased against the tall, and height/weight^3 is very biased against the short. Height/weight^2 has a pretty flat average, and doesn't look worse for the tall.
posted by a robot made out of meat at 5:24 PM on May 23, 2008 [3 favorites]