Friday, November 11, 2011
What is BMI?
Yesterday, I mentioned that discussing your BMI with your doctor might be a less emotionally charged way to discuss your weight. Terms like "overweight" and "obese" tend to make us all shut down and stop listening, but it is really important to understand whether or not your weight is becoming a medical issue. The BMI is your "Body Mass Index", and it is a reflection of your relative body fat. Note that I said "reflection"- the BMI is NOT a precise measure of your body fat percentage.
BMI is simply calculated by using a person's weight and height. Specifically, BMI equals your weight in pounds multiplied by 4.88, divided by the square of your height in feet. There are charts to look at and on line calculators as well. Click on this link to the U.S Dept. of Health & Human Services' BMI calculator to see what YOUR BMI is today.
Now that you've got your number, what does it mean? Well, if you are less than 20, you are underweight. If you are between 20-25, you are considered healthy, or "normal" weight. Please pay attention if you are in the 25-29 segment, because you are overweight! If you are >30, you fall into the medical definition of obesity.
Why did I bold face that 25-29 segment? Because in my clinical experience, no one with a BMI of 30 or more is surprised that they weigh too much. However, I would estimate that over HALF of my patients who fall in the "overweight" category are shocked that they have a medical issue with their weight. After college, people often put on a couple pounds per year, very slowly creeping that scale. During that time, they may only go up a size or two in clothing, especially if they are buying more expensive clothes (which tend to run larger and larger.) Before they realize it, they weigh 20 or 30 pounds more than is healthy, yet they don't "feel fat". I don't care very much about cosmetic issues with weight, but I care deeply about increased risk of diabetes, heart disease, low back and joint pain, all of which come into play when your weight goes up.
BMI's are not flawless. If you are an "ARNOLD" with tons of huge muscles, your BMI will be falsely elevated. If you are elderly and frail, chances are good that your BMI underestimates your body fat. In general, however, the BMI is a great tool to assess your weight.
BOTTOM LINE: Take a moment and calculate your BMI, and take an honest look at your weight: 1/3 of Americans are overweight, 1/3 are obese, and only 1/3 are normal or underweight, so the odds are stacked against you.