BMI calculation too hard, say doctors

There has been a report shown on Sky News today. Some doctors find the Body Mass Index calculation "mind numbingly complex"
 
The formula is simply  BMI = weight/height squared. If a doctor finds this maths too complex, that is seriously frightening.

That's hard to believe. Perhaps they mean it's too hard to explain to their patients?

If you're dealing with pounds rather than kilograms, the formula is (weight  / height squared) x 703. Not surprising that MDs or anybody else can't do that in their head. But that's why they have a chart hanging on the wall.
 
For somebody like me, no calculation is required. The doc takes one look at me and says "you're too fat.". Yup, same as the previous diagnosis.

bitflipper
 
For somebody like me, no calculation is required. The doc takes one look at me and says "you're too fat.". Yup, same as the previous diagnosis.

A good eye may be a useful metric. The problem with BMI, is that it is only a rough estimate for an individual. The actual measurement of the fat content of the body is fiendishly difficult, something like trying to find the weight of cashews in a paper bag full of mixed nuts without knowing how many other nuts are inside. In a large population that estimate may be very useful, and it is easily calculated (by a computer at least) from two commonly available and cheap measures. Thus it is a very useful tool for research studies looking at the health effects of obesity or fat loss. But even if you know the amount of total body fat relative to lean body mass, it is not at all clear that such a number will provide accurate risk estimates for an individual. The location of the fat (visceral vs subcutaneous) and type of fat may be important in the health effects of adipose.
 
http://en.wikipedia.org/wiki/Body_fat_percentage
 
So measuring the BMI in a population may be useful in interpreting health impact, but is does not necessarily imply that it should be used uncritically to guide decisions for a given patient. If your doctor sees a big gut, but cannot pinch a significant amount from the abdominal wall, or an embarrassing large butt and thighs but not much gut, he may well be correct in estimating that you are at substantially less health risk than your BMI would suggest.

Think it was just a bit of very poor journalism. (It was Sky News after all, I think it was the reporter that found the formula mind numbingly complex).
 
There was a better report later, I think they must have read this fred because they mentioned many of the points brought up here.
 
 

Most probably your scale is using bioelectrical impedence analysis (BIA), which measures a change in electrical current that is in theory proportional to the the water density of the body i. e. the proportion of your body mass that can be attributed to water. By comparing the estimated water content to the weight measured, a calculation can be made to estimate the weight of the body related to fat content. Usually that will be expressed as a percentage:  
body fat/ body weight x 100
The scale is trying to say that fat represents 17% of your body mass. 
http://en.wikipedia.org/wiki/Bioelectrical_impedance_analysis
 
This type of measurement may or may not be accurate for a given individual, even if done with the best available equipment. If it is consistent (repeatable on multiple measurements) for an individual, it may show some real utility in determining if weight loss or gain is due primarily to fat or muscle changes. Building muscle mass (lots of water) will show up as a relative lowering of fat %. so at least it has the potential to discriminate between fat and muscle, which the BMI does not. The body fat percentage has been used in very few studies, so the ideal number is less well established. But 17 % would be in a healthy range by commonly quoted standards.
http://www.builtlean.com/2010/08/03/ideal-body-fat-percentage-chart/
 
If during setup of the scale you input your height into the scale/computer, it can give you an exact calculation of the BMI,  which is a calculated surrogate metric that is usually correlated to obesity. Relating the BMI to the body fat percentage is not a simple calculation for an individual, and unfortunately the popularity of the BMI in research means that most of the inferences drawn from studies on obesity and health risks are only available for BMI correlations.