The BMI is also not meant for children under the age of 18. During these years the body is growing fast and that affects the calculation. For children we use different, age specific, tables. The Center for Disease Control (CDC) provides the following ranges for BMI values for adults:

The major use of the BMI has always been its ability to indicate your risk of disease – heart disease, stroke, high blood pressure, and diabetes. But even this “cast in stone” use of the BMI is in doubt.

A recent study published in the Lancet on 11/5/2005 studied the BMI as a predictor of heart disease in a group of 27,000 participants from 52 different countries. What they found was that BMI was essentially useless as a predictor of heart disease. Once other risk factors were accounted for there was no predictive benefit from the BMI.

What the study did find was that the waist to hip circumference ratio was a strong predictor of heart disease. The odds for heart disease for each quintile (every group of subjects consisting of 20% of the individuals – i.e. the bottom 20% or top 20%) increased dramatically. The second quintile was 15% more likely to develop heart disease; the third was 39% more at risk; the fourth was 90% more; and the fifth was 2.5 times more like to develop heart disease than the lowest group of subjects.

Before you jump up and scream that everybody uses it, you're right they do. AND BMI is a predictor and can predict total body fat and subcutaneous fat with 88% accuracy. It is also relevant to predicting diabetes and heart disease as well as other disease. What I am saying is, that IF you use waist circumference AND you account for other known risk factors of heart disease THEN the BMI has no value in predicting heart disease. That's it, nothing more.

EQUATIONS

The BMI has been used to estimate body fat, and in particular subcutaneous fat (SAT) with fair results.

SAT(cm 2) for men = -621 +[9.37*BMI] + [5.51*hip circumference] (R 2 = .87; SEE 32.1)
SAT(cm 2) for women = -332.9 + [24.5*BMI] + [2.26*age] (R 2 = .87; SEE 61.7)
From Bonora et. al, 1995. These equations explain roughly 87% of SAT.

Deurenberg developed equations to predict total percent body fat (%BF) relative to underwater weighing.

Children
BF% = 1.51*BMI - 0.70*age - 3.6*sex + 1.4 (R2 0.38, SE of estimate (SEE) 4.4% BF%).
Adults over age 15
BF% = 1.20*BMI + 0.23*age - 10.8*sex - 5.4 (R2 0.79, SEE = 4.1% BF%).

In 1998 Deurenberg developed another equation bsed on a review of several studies that included 11,924 total subjects.

BF% = 1.294*BMI + 0.20*Age – 11.4*[gender, male=1, female=0] – 8.

NOTE: this equation is based on European Caucasians. It is relatively accurate (on a group level) for European Caucasians. In American Caucasians it overestimated fat by 3.8% body fat. In Chinese it underestimated fat at lower BMI levels and overestimated at high BMI values. In Polynesian and Black populations it overestimates body fat. In Indonesians, Thais, and Ethiopians it underestimates body fat. This highlights the fact that BMI is not a great predictor for the individual as it varies by the composition of the individual’s weight and factors such as age, ethnicity, body build, and frame size.

MY CONCLUSION

Use the BMI, but realize its limitations. It does not measure fatness. It has several means of error. Pay more attention to your weight and waist circumference.

By the way, here is how you calculate the BMI:

BMI = [weight in pounds/(height in inches x height in inches)] x 703.

For example, a person that weighs 220 pounds and is 6 feet 3 inches tall has a BMI of 27.5

[220 lbs/(75 inches x 75 inches)] x 703 = 27.5

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