BMI stands for body mass index. Essentially it is a mathematical equation that compares your weight, or mass, against your height. As children develop from infancy through the teen years, pediatricians have similar growth charts that compare the child’s height, weight and height to weight against what are comparative norms. Children may fall in the five percentile for height and weight against their peers but be in the 50 percentile for height to weight.
This is a similar measurement for the BMI that compares your weight and height against your peers. Pediatricians use a graph to plot the height to weight measurement while the BMI uses a mathematical equation which gives you a two digit number against which you can compare your results.
The BMI equation was actually developed between 1830 and 1850 and is the mass divided by the square of an individuals height expressed in kg/m2. This unit of measurement has been used by the World Health Organization as the standard to define obesity since the early 1980s.
Insurance companies in the United States are using the BMI as a cut off point to raise insurance rates or deny coverage for high risk patients. The cut off point is different for every company, while others will put surcharges in place to allow coverage.
The calculations will place a weight to height comparison in one of eight categories:
Very Severely Underweight – Less than 15
Severely Underweight – 15-16
Underweight – 16-18.5
Normal – 18.5 to 25
Overweight 25 to 30
Obese Class I 30 to 35
Obese Class II 35 to 40
Obese Class III over 40
In the recent years, it has become more apparent that the measurement does not account for individuals who have a higher muscle mass accounting for higher weight, or who are taller because mass does not increase on a linear scale. In a study in 2008, the National Health and Nutrition Examination Survey found under counted obesity rates and those in the mid range between 20 and 30 had a wide range of body fat percentages. (1)
Despite some of the inaccuracies of the BMI, women can use this measurement as a way of comparing their relative health risk against their peers and then against their own values as they gain or lose weight.
You can calculate your BMI at home when you know your height and weight. In kilograms and meters the formula is: weight/height squared. In pounds and inches a conversion factor is required to make up for the differences in the metric system. The formula is weight/height (inches) squared multiplied by 703.
It is important to remember that body weight is not the only indicator of your overall health or of a healthy weight. Waist circumference, body fat measurements, blood pressure and insulin resistance should also be considered. However, because the BMI is a quick and easy way to compare your measurements against your peers, it continues to be used.
Take a strong look at your overall health and set aside your desire to be model thin. Instead, your best weight may be the one you can maintain over years which keeps your visceral/belly fat low and increases your muscle mass. Your goal is to maintain a healthy weight that allows you to enjoy your life.
References:
(1) National Health and Nutrition Examination Survey
http://www.faqs.org/nutrition/Met-Obe/National-Health-and-Nutrition-Examination-Survey-NHANES.html
Resources:
Vermont State: Adult Body Mass Index
http://healthvermont.gov/family/fit/documents/RevisedBMI3-07.pdf
Centers for Disease Control and Prevention: About BMI for Adults
http://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/
National Heart, Lung and Blood Insitute: Calculate Your Body Mass Index
https://www.nhlbi.nih.gov/guidelines/obesity/BMI/bmicalc.htm
American Insitute for Cancer Research: How to Measure Your Risk
Time Magazine: What’s the Ideal BMI for Longevity
http://healthland.time.com/2010/12/03/whats-the-ideal-bmi-for-longevity/
Leave a Reply