The effectiveness of the Body Mass Index (BMI) scale has long been under scrutiny. The scale is used to gauge obesity, overall health, and the risk for disease. But just because it is a staple of medical assessment doesn’t mean it should be.
The BMI overlooks a number of key details, most importantly an individual’s body composition and shape. For example, a person who is 5 ft. 7 in. and weighs 165 lbs. who has 10% body fat would have the same BMI as a person who has 30% body fat, but is of identical height and weight. Both are characterized as overweight, but the one carrying 20% less fat is lean, likely far healthier, and does not carry the same health risks associated with extra weight that a person with the higher fat percentage does. The difference is where the mass comes from. The leaner individual is made of muscle and lean body mass, while the fatter one is carrying a high amount of unhealthy body fat.
It’s important to take body composition into account because where a person carries their fat—and how much they have—severely impacts overall health. That’s why a father-son doctor combo has come up with a more effective and accurate scale to measure weight, health, and disease risk. It’s called A Body Shape Index (ABSI) and pays careful attention to the important details the BMI scale misses.
Fat around the gut is associated with an increased risk of high blood pressure, cancer, diabetes, heart attack, and stroke. This is not only true for people with a high BMI, but for those with a low BMI, too. Some people who appear skinny still carry a lot of body fat, giving them a body type commonly referred to as “skinny fat.” Both of these groups can carry substantial visceral fat around the belly, some showing it more than others. At the end of the day, you want to pay attention to your total fat mass.
ABSI, which takes body shape and composition into account, has proven to be more effective at measuring obesity-related illness than BMI. The developers looked at data from 7,011 adults over 18 that participated in a large-scale British health and lifestyle study called HALS1. The study began in 1980 and was followed up in the HALS2 study seven years later.
The research team then examined National Health Service records from 2009 to identify deaths and cancer cases in participants. As of 2009, 2,203 deaths of the 7,011 participants had been recorded. Next, they compared those numbers with the all-cause mortality rates from the sample population and applied the ABSI, BMI and other variables like waist-circumference, waist/hip ration, and waist/height ratio and noticed the ABSI was the best way to identify mortality hazard.
They noticed people with an ABSI in the top 20% had death rates 61% higher than those with an ABSI in the bottom 20%. To get further confirmation of the effectiveness of their scale, the team looked at a similar American lifestyle study conducted between 1999 and 2004. The numbers were very similar to what they found with the British study.
So what does all this mean? Have you and your doctor been wrong in using the BMI to guide your overall health and obesity risk all these years? I’ve never been a big fan of the BMI and have always taken it with a grain of salt. When it comes to having a healthy weight, it’s really important to pay attention to your body composition. You want to have a good lean mass to fat ratio and try to keep body fat percentage below 25%, regardless of your shape or size. The more lean mass you have, the less risk you carry for diseases associated with being overweight.
“Body Shape Index As New Predictor of Mortality,” Science Daily web site, February 24, 2014; http://www.sciencedaily.com/releases/2014/02/140224171603.htm, last accessed March 3, 2014.
Davis, J., “The Risks of Belly Fat,” WebMD web site, http://www.webmd.com/diet/features/the-risks-of-belly-fat, last accessed March 3, 2014.