My Take on BMI

I'm tired of hearing professionals advise individuals to use BMI as a tool to find if they're at a healthy weight. I wrote this as one of my wellness tips for work.

The Problem with BMI

Body Mass Index, or BMI, is a popular way to analyze whether someone is at a healthy weight. It has become so popular due to it’s user friendliness – you only need to know your height and weight and then a simple chart gives you a number which classifies you as underweight, normal, overweight or obese. Simple, but there are some problems with this method. Anyone who has more muscle than an average person will register with a higher BMI, even when they maintain very low body fat. For example, Jay is 5’9” and weighs 274 pounds. This puts his BMI at 40 which is classified as extremely obese. However, Jay is a professional bodybuilder who maintains 3% body fat – about as low a human being can get. Another problem with the BMI system is for those who have less muscle than an average person – and this is becoming more common in our ever-more-sedentary society. For example, Rebecca is 5’6” and weighs 135 pounds. This puts her BMI at 22 which is considered normal. However, Rebecca has 30% body fat, which is too high to be considered healthy.
Bottom line: Everyone has different amounts of muscle mass due to genetics and lifestyle factors, but the BMI charts assume everyone has the same amount. For this reason, BMI is a good way to analyze large populations of people, but not individuals. A better way is to use body composition, or body fat percentage. To measure your body composition you will need to use some type of device. Most body fat scales for home use are not very accurate. Personal trainers and other fitness professionals may use a caliper to measure folds of skin on various parts of the body. This method is accurate, typically within a 3-4% margin of error, but it is subject to human error. Many gyms have ‘bioelectric impedance devices’ which have about the same margin of error as the skin-fold method. The most accurate way to measure body fat is ‘hydrostatic weighing’ which is done with your whole body submerged in water. Hospitals typically have the equipment necessary for this type of procedure.