Saturday, February 09, 2008

If I had a (smaller) hammer . . .

To a hammer, everything looks like a nail. And the proverbial hammer we often talk about is the BMI, a simple height/weight ratio that's more and more being used to identify and punish everyone from schoolchildren to the lederly for being fat.

Of course, BMI is a crude tool, a hammer, if you will, because it doesn't take into account muscle mass, or percentage of body fat, or anything beyond height and weight. So most athletes fall into the overweight if not obese category, according to BMI charts. Tom Cruise's BMI makes him obese, because he's short and densely muscled.

Now, finally, someone somewhere is paying attention. In a study published in Nutrition Journal, researchers at the University of Pavia in Italy did a small study looking at how weight loss recommendations would change for a group of people when they applied different measures of overweight:

The researchers obtained each person's BMI as well as body-fat measurements including waist circumference and total percent body fat. The also calculated a measurement similar to BMI that identifies fat mass called body fat mass index. The investigators then compared the percentage of the study group that would be told to lose weight according to each calculation.

BMI calculations, they found, identified 11 percent of the group as needing strong recommendations to lose weight and 41 percent as needing basic recommendations to lose weight. By contrast, waist circumference measurements indicated about 25 percent would need strong recommendations to shed pounds and 36 percent would need basic weight loss recommendations, Colombo said.

Moreover, 29 percent and 48 percent would have received similar weight loss recommendations according to total percent body fat measurements, while 21 percent and 54 percent would receive the same, according to body fat mass index.


The lead researcher, Dr. Ottavio Columbo, concluded, "Using criteria based on body adiposity (fatness) rather than body weight would result in a much greater proportion of the study population receiving recommendations for weight loss."

Yeah. We coulda told you that. But hey, it's a start.

7 comments:

Nancy Lebovitz said...

Another quirk of the BMI: Speaking as a very short-legged person, I suspect that I'd be heavier at a given body composition than a long-legged person of the same height. A torso is further around (and presumably heavier per inch) than a pair of legs.

Harpy said...

Another flaw with the BMI is that it's based on the SQUARE. When a 3-d object increases in size, the measurement goes up by the CUBE. Even taking into account that human heads don't get appreciably larger the taller the body, this means that a person who is 5' could fall in the BMI category of 'obese', but someone who is 6' but who has the same body composition and roughly the same proportions as the shorter person could be in the low end of 'overweight'. And someone 6'6" again proportioned the same might be 'normal'.

The BMI is flawed in so many ways. I cannot believe people, scientists with mathematical training even, seriously think it can indicate anything except...BMI.

Harriet said...

As a woman who's going through menopause, and shrinking, I've had the uncomfortable experience of having my BMI go up even though I haven't gained any weight.

Which sucks.

The whole thing is just so ridiculous.

Tanizaki said...

The lead researcher, Dr. Ottavio Columbo, concluded, "Using criteria based on body adiposity (fatness) rather than body weight would result in a much greater proportion of the study population receiving recommendations for weight loss."

Yeah. We coulda told you that. But hey, it's a start.


In the above passage, you indicate approval of body fat to inform weight loss decisions, but here:
http://harrietbrown.blogspot.com/2007/11/mom-im-too-fat.html

you sneer at calipers. Can you please reconcile what appear to be inconsistent positions?

Harriet said...

No, I'm not indicating approval of body fat to inform weight loss. I'm indicating approval of fewer people overall getting the advice to lose weight.

I don't think anyone should be advised to lose weight. I think people should be advised to eat well, exercise, and take good care of themselves. And love themselves whatever shape and size they are.

Anonymous said...

Maybe I'm confused, but doesn't this study say we should tell MORE people to lose weight?


"Using criteria based on body adiposity (fatness) rather than body weight would result in a much GREATER proportion of the study population receiving recommendations for weight loss."

Harriet said...

Hmmm. That's not how I read it the first time, but I think you are correct.

I was looking at the numbers--41 percent initially got "basic" weight loss recommendations using BMI, while 36 percent would get those recommendations using waist circumference.

My bad here, anonymous. This is a case of reading what you want to read instead of reading what was there. Thanks for pointing it out.