What does "overweight" really mean, anyway?

Just this morning, I went to see a new doctor. As part of all the procedures that we went through, she weighed me and measured my height. I knew what dastardly tricks she was up to: My doctor was calculating something called my BMI -- short for "Body Mass Index." It's a very simple method of classifying people's body-types, typically used to determine possible health risks. Essentially, you take a person's weight and divide it by their height squared.

(Okay, it's slightly more complicated than that because you need to have the weight in kilograms and the height in meters, instead of pounds and feet like we use in America. Fortunately, some easy multiplication can change our units of measurement into the correct form.)

The formula for BMI is:

So, you take a person's weight (in pounds) and multiply it by 703. Then, divide that product by the person's height (in inches), squared.

This may seem confusing so far, but let's think about what the BMI is figuring out. It's looking at two things: weight and height. Where have you seen a height squared before? (Phrased differently: What happens when you multiply a length times itself?)

Area=a²
The Area of a Square is found as the length of one side squared. This is just like what the BMI tells us to do with a person's height: Mathematically, the BMI flattens and stretches out a human body into a square that's as tall and wide as the person's height.

But overall, BMI is the person's weight divided by the person's height squared. So what does that mean? Basically, it determines how heavy each little square inch of the person's flattened out body is; it's some number of pounds per square inch (Rather it's the number of kilograms per square meter).

Okay. Now that we know how to figure out a person's BMI, let's calculate one real quick: mine. As of this morning, I am:

• 5'9.5"= (5 feet X 12 inches) + 9.5 inches = 60 inches + 9.5 inches = 69.5 inches
• 193 pounds

So,

• We square my height:
• (69.5 inches)²=4830 inches²
• Read aloud, that's: "Four thousand, eight hundred and thirty Square Inches"
• And divide my weight (times that conversion factor) by the height squared:
• (193 pounds X 703)/4830 square inches = 28

But what the heck does "28" even mean?

The World Health Organization has a handy chart that it gives to doctors around the planet to figure out health risks for patients based on their BMI:

BMI	Classification
Less than 18.5	Underweight
18.5–24.9	"Normal" Weight
25.0–29.9	Overweight
30.0–34.9	Class I Obesity
35.0–39.9	Class II Obesity
Over 40.0	Class III Obesity

So, according to the WHO, I am Overweight. This basically means that I have a slightly increased risk for certain types of cancer and possible heart problems over people who have a "Normal" BMI. This is where the problems start.

For a person with my height to have a "Normal" BMI, I would have to weigh somewhere between 127 and 172 pounds. I'll admit, if I lost 20 pounds, I'd be a little better off -- although I'd be skinnier than looks healthy for someone with my frame. According to the BMI, however, 172 pounds is supposed to be my maximum weight. They're saying that I could even weigh down to 127 pounds and be "Normal." If I weighed 127 pounds, I would be a sickly little thing that gets blown around by the wind. Even my doctor would tell me to gain a little weight.

All types of groups are against the BMI system for various reasons: 1) It identifies one group of people as Normal... which implies that people outside of that group are Abnormal. 2) The "Normal" group isn't necessarily the healthiest for many reasons, including the fact that 3) it doesn't take into account much human variation.

(I'd like to point out, specifically: studies have shown that people in the "Overweight" and some in the "Obese I" range of the BMI have the lowest risk for some types of heart disease.)

There are much better systems out there, including the Waist-Hip Ratio. This system is also pretty easy to compute: Divide the length around of your waist -- up near your belly-button -- by the length around of your hips. Females should shoot for the ratio 0.7-0.8, and for males, the ratio should be 0.9-0.95. These are only rough figures, since more research still needs to be done. But, in fact, a new study just came out confirming that Waist-Hip Ratio is better as a health indicator than BMI. (They examined 359,387 different people and came to that conclusion!)

As my doctor weighed me this morning, I told her that I don't buy the BMI system and that I believe there are better ones out there. She responded: "Then, I won't tell you that you should lose a couple pounds."