02 January 2006

Body Mass Index

Body Mass Index, or BMI is a quick and easy way to determine whether you are overweight, obese, or healthy. It is a simple indicator that compares your height and weight to what is healthy. One thing to note is that this is (in my estimation) a crude method of determining your ideal weight, as it does not take into account different body types, though it could also be argued that the myth of different body types is simply and excuse for maintaining an inappropriate weight. Hm, I'm going to have to look up info on body types now...

According to the US Dept of Health and Human Services's Heart, Lung, and Blood Institute, BMI of less than 18.5 is underweight, 18.5 to 24.9 is healthy, 25 to 29.9 is overweight, and greater than 30 is considered obese. If you just want to determine what weight is healthy for your height, their handy-dandy table is a good resource for that. (It's worth noting that the table is more crude than the calculator, with one less decimal place.)

For example, a person with a typical woman's height of 5'4" should weigh no more than 140 lbs to be healthy, and would be considered obese at around 175 lbs. A person at a typical man's height of 5'11" should weigh no more than 180 lbs to be healthy, and would be considered obese at around 215 lbs. The AP (CNN) suggests that surgery, such as stomach stapling and other gross things, not be considered until a BMI of 40 (around 235 lbs in the average woman or 285 lbs in the average man). This can be reduced to a BMI of 35 (205/250 lbs) if there are other "weight-related medical problem(s) like diabetes or high blood pressure." (AP/CNN)

I am glad to say that I am on the underweight edge of healthy, at a BMI of 19. My mother has Type II diabetes, and I suspect is at least overweight, if not obese, but I don't actually know her weight. I do know that she doesn't appropriately monitor her diet or ever exercise, and she probably needs to increase her insulin dose, but she is still in denial about it all (some 4-ish years after first diagnosis). Sad.

6 comments:

utenzi said...

Congrats on your weight, ZP. I'm more like your Mother. My BMI is 29 so I'm overweight and almost obese. Uh-oh!

j_ethereal said...

The BMI is great for an estimate of how under/overweight you may be. However, it is not very accurate for some individuals (athletes in particular). In my opinion, the best measure would be an estimate of your body fat percentage. Body fat percentage can be estimated by using skinfold calipers. The skin is pinched with the fingers and a linear measure of the distance between the caliper arms is recorded. This is done at several locations on the body. These values are then plugged into a regression equation ultimately yielding a body fat percentage. However, the "gold standard" for measuring body fat percentage is underwater weighing which utilizes Archimede's principle. To really be accurate, a measure of the residual volume of your lungs needs to be done. It's been a while since I studied this stuff but I believe that this involves an oxygen rebreathing technique. Estimates of residual volume can also be made from height and weight. The underwater weighing procedure is as follows: The individual sits on a chair (which is suspended from a scale)in a pool of water. The person is then instructed to go under water and exhale as much air as possible. When they are in this position, their weight is recorded. Taking into account the residual volume of air left in the lungs, this underwater weight represents the individual's body volume. Knowing their actual weight on land, you can calculate their body density. This body density is then plugged into an equation (derived from cadaver data) to give the body fat percentage.

Tom said...

Ah, happy to say I'm solidly in range at 21.5. Diabetes is nothing to fool with, kidney failure is no fun. Could well be denial. My Dad didn't look after his and now he's looking at dialysis, sadly it could have been prevented.

zandperl said...

Thanks, but I deserve no more credit for it than I do for my eye color, but unlike eye color, my weight will likely deteriorate as I age. I am currently lucky that without any dieting or exercise I maintain a scrawny 120 (+5/-10) lbs. I once had a doctor tell me to try and put on weight, and I couldn't. :-P But yeah, I keep trying to start exercising, and it keeps not happening. It's on my to-do list. ;)

zandperl said...

(that last comment was to Utenzi)

J_eth:
And that's exactly my point! At the same time in life when my doctor was telling me to put on weight, my gym teacher did that caliper test and I came out overweight (over-fatty?). I swear, tomorrow I'm either going snowshoeing (up to 20" predicted!) or I'm googling/calling around for a folkdance studio.

Doctor Marco said...

I believe that BMI is good enough. It is true that in truly muscular people, we could use other methods to measure fat, like calipers or electrical impedance. BMI is cheap and can be aplied to anyone in the world. It is useful when assessing the individual patient and when assessing the population in epidemiologic studies.

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