BMI Realization

[WakefieldWendy]

You know, I always had a bit of a hate-on for BMI. I thought it punished people for having muscle. I am certainly more fit and more lean that most women with my BMI for example.

However, I was chatting with a guy in my office who played football in university (in Canada). He was a center and above 300 lbs in his playing days. He said something to the effect of, it doesn't matter if you can bench 340, your heart doesn't know the difference between fat and muscle.

I think I understand what he's saying. From a heart perspective, your heart is supporting all your tissue, whether it is muscle or fat. So super-huge muscle guys are still putting a load on their hearts.

I imagine BMI is still a gross oversimplification. For one thing, if you have greater than average muscle, you probably have greater than average heart capacity.

So I guess I'm saying that while I think body fat percentage is probably a more useful measure of obesity than BMI, I am beginning to think that BMI probably is also a useful measure of something.

Thoughts??

[laughingW]

That's a point, certainly. Even Ahnold took off mass when he was no longer competing in bodybuilding.

However I still disrespect BMI. What I don't like about it is not only the muscle issue but that it lumps together dense-boned people and light-boned people. Weight is simply too crude to rely on as a health predictor.

Height-to-waist ratio, like they use in the UK, is the best predictor of disease of all of them, better than BMI and better than waist-to-hip ratio. I read that the only reason not to change over to that, is it's too much work! BMI is already entrenched.

[maxlharris]

First in the queue: Everyone who talks about BMI responsibily notes that it doesn't have much to do with people at the tail ends of the curves, specifically the muscular end of the curve, athletes. I suppose you could have a very nonmuscular person with significant adipose tissue at the other end of the scale who registers a healthy BMI despite having a high amount of body fat. But the people who talk about BMI with knowledge suggest that high amounts of muscle render people outside of the predictions and curves of BMI. People like you and I probably don't get to opt out of BMI, but people like Derek Jeter, David Beckham, Sid Crosby, Steve Nash and Mia Hamm probably do.

Second: BMI is a very blunt, gross instrument. Fat %age is a little sharper, but is still very blunt and gross. More important than the quantity of fat is the deposition of that fat, as either visceral adipose tissue or as subcutaneous adipose tissue. BF% doesn't tell us anything about that.

Third: Your heart doesn't know the difference between muscle and a volkswagon. It's a muscle. The nerves drive it to function in response to needs. Muscle at rest puts more demand on it than fat at rest. But, like every other muscle, your heart can get stronger and more efficient or can atrophy. I suppose you can create an undue amount of stress on your heart by being a competitive body builder, but is it the possession of muscle or the activities required to get it that is the problem. That said, I'd rather have a strong heart, supporting strong muscles, without a bunch of visceral adipose tissue clogging up the works and getting in the way of proper heart function. Oh, and I'd like to minimize the oxidative stress that would lead to blockages. And all that other good stuff for good heart health.

Conclusion: Is BMI as useful measure of something? Probably for most people we know. Is BF% more useful? Again, probably (I would say definitely). Is either really the alpha and omega? No. Not anymore than the scale or tape measure.

Last thought: I'd rather have a high BMI with a low-moderate bf% than a high BMI with a high bf%. But that might be just me.

[WakefieldWendy]

Third: Your heart doesn't know the difference between muscle and a volkswagon. It's a muscle. The nerves drive it to function in response to needs. Muscle at rest puts more demand on it than fat at rest. But, like every other muscle, your heart can get stronger and more efficient or can atrophy. I suppose you can create an undue amount of stress on your heart by being a competitive body builder, but is it the possession of muscle or the activities required to get it that is the problem. That said, I'd rather have a strong heart, supporting strong muscles, without a bunch of visceral adipose tissue clogging up the works and getting in the way of proper heart function. Oh, and I'd like to minimize the oxidative stress that would lead to blockages. And all that other good stuff for good heart health.

The guy I was speaking to (and he wasn't speaking about BMI, but more generally about keeping his weight down) wasn't a body builder but an Offensive Lineman. Some of those guys are 340 lbs, full of muscle, but not lean. I guess what I'm saying is, some of those guys probably have a within range bf%, but their total mass is still hard on the heart.

I don't sweat this stuff personally. I'll never be thin, and I'll probably never even be in the "healthy" range (i.e. correct BMI, bf% lower than 30). I'd be happy to get out of obese and into "overweight", edging towards "average". BMI comes up for me because we are trying to have children. First, some countries/places won't let you adopt if your BMI is too high (mine is 35.9 right now, so I think that's OK). Second, although we are trying IVF with my DW now (in Feb), if something goes wrong and we have to switch to me, they won't do IVF if your BMI is over 35. I cross that magical line in about 6 pounds, so think I can reach that by the time we'd decide that I need it.

Does anyone know of any height-weight tables? That sounds pretty cool.

[maxlharris]

What I'm suggesting is that an offensive lineman might not know if it's his muscle that is working his heart hard or if it's carrying around the fat. Or even the nature of the game. Considering that a number of linemen (both lines) have bellies that stick out past their shoulder and chest pads, I wouldn't say they are really within range. But considering that for a lot of them (interior linemen especially) the job is to be massive and hard to move, carrying extra weight is probably not a problem.
.
.

http://www.talkingnfl.com/wp-content/uploads/2007/06/10309622451press620200742525pm.jpg
(Is this man within range? He has been to the pro bowl 4 times)

Now, Ted Washington is not your typical guy, even for an NFL lineman. But the question of whether it's muscle weight, fat weight, or opponent weight that's hard on their systems is something they probably cannot answer. It's one of those questions that's hard to know without a post mortem inspection.

As to you being in the "healthy" range, that's probably an inherent flaw in the measurement. You can be in your "healthy" range. Whether that's good enough for your IVF doc or not, I dunno, but given all of the flaws with BMI, I think it makes the strongest case against it. If you can be healthy without being in the "healthy" range, doesn't that suggest that the metric is broken? It does to me.

[LisaS]

my take on BMI is that it is a (probably) useful screening and statistical instrument for populations, but not terribly useful at the individual level.