Is the BMI (Body Mass Index) Accurate?

Fit people of any weight are healthier than unfit people of any weight. The President's Council on Health and Fitness cites this; hundreds of professional medical journals have stated it; medical institutes worldwide have stated it. Fitness, not your BMI or body weight, is what determines your health. You can be overweight, even obese, and healthy.

But there's a caveat. You must also be fit. Today, fewer and fewer of us are fit. We simply don't exercise. Weight has nothing to do with fitness; there are just as many skinny out-of-shape people as fat ones. Unfortunately, the trend toward sedentary lifestyles is growing, and our children are the ones suffering for it, as they are growing up in a world where the norm is to eat fast food and sugary snacks while sitting in front of the television or computer.

This was part of the problem facing nutritionists and weight experts in the early 1980s, when television and office work became normal and farm work and physical labor became the exception. How do you help inactive people determine whether they are at a healthy weight?

Enter the BMI, a 150-year-old technique. Imported from a world totally different from the one we live in today, the BMI has become a Bible for obesity measurement.

How Do You Identify Too Fat? The BMI

The BMI, used today by almost every doctor to determine your state of fatness, was developed in the 1830s. It was not designed to be a medical tool, but rather a sociological means to determine a person's rough weight in relation to an ideal weight, and it was defined by one man.

Adolphe Quetelet was one of the first social scientists whose primary goal was to define the "average man." Problem is, the average man in 1830s Europe was quite different from the average man in modern America - ethnically, medically, socially, nutritionally, in regards to activity level, the early Victorians were very different from modern people.

Still, in the 1980s, health professionals picked up this old means to measure relative fatness or thinness as a godsend -- a way to numerically define one's weight in a way they could use to discuss losing weight with their overweight clients. In doing this, they grandfathered in a system that was never meant to measure health -- though it is used that way today.

The BMI is inaccurate with athletes - with various ethnic groups - with mesomorphic (usually heavily muscled) and endomorphic (wiry) body types - with the aged - even with nonobvious differences in bone structure. How could the BMI for Dolly Pardon make her equivalent to someone built like Twiggy? How do you measure a healthy "booty" size when African women are built so differently from the Europeans this scale was developed for? Why do so many beefy football players and Marines who are obviously very fit measure as overweight and sometimes even obese by the BMI's scale?

The BMI, which is the guideline to which most doctors adhere, is nearly 200 years old, developed by a single person, and has many, many inaccuracies. How can it be trusted as a means to measure obesity?

Alternatives to the BMI

Slowly but surely, healthcare professionals are starting to realize just how bad the BMI is at accurately determining body fat. Fortunately, there are dozens of other methods for measuring your level of fatness.

Hydrodensitometry involves immersing the subject in a big vat of water to measure overall body density. This may be the most accurate means for measuring body fat. Water that is displaced by the body is measured, and a formula is applied to this volume of water compared with the weight of the subject to get a very close approximation of the subject's real body fat percentage.

Fatfold Measures use a set of calipers on several parts of the body to measure the size of, well, fat folds. Formulas developed by researchers are then used to get the body fat measurements.

Bioelectrical impedance (shudder!) uses electricity passed through the body, with the current leaving measured, to determine how much fat is in different parts of the body. Fat and muscle have different electrical impedance values, so a good measurement of current can give a good idea of body fat levels.

Waist-Hip Ratios is the most promising simple measure of, not body fat, but relative health. Lower waist sizes measured at the bellybutton line when compared in a ratio to hip size indicates a person who may be fat, but who is most likely healthy. The larger the waist in relation to the hips, the less healthy the subject. In women, the waist-to-hip ratio should be 0.80 or less for good health (waist measurement/hip measurement There are many other methods, from circumference measurements (spoken of, believe it or not, in the classic book Gulliver's Travels by Jonathan Swift) to advanced CT and MRI scanning. For measuring a ethnically varied and modern population, just about any of them is likely to be an improvement on the BMI.