Recently I’ve started thinking about different metrics that are used to assess your level of health. Body Mass Index (BMI) is, and has been for around 200 years, a metric that many swear by. But just a quick Google Search for BMI Origins will reveal a very strange history of the measure, and plenty of people pointing out that at best it’s a crude measurement and at worst, it might be racist. Regardless of it’s origin, you can’t argue with the calculation: Divide weight (in kilograms) by height (in meters). When I was at my largest, my BMI was a whopping 53.30. Given that the standard cut offs are 25+ is overweight, 30+ is obese, and 40+ is morbidly obese, I was in pretty poor shape. As of this morning, my BMI is 24.85, just below the cut-off for overweight (My weight this morning was 193.6, and I am 6 ft, 2 inches tall).
So yeah, BMI tells you that you’re screwed. But is there another metric? Enter the Fat Free Mass Index, which has been around for around 20 years now with normed values for the Caucasian population. Whereas BMI does not tell you anything about someone’s body composition, FFMI does tell you what proportion of the body is made up of lean tissue (muscle) and bone, versus what is made up of fat. The equation is below:
FFMI = fat free mass [kg]/ (height [m])²
Looking at research, we find that higher FMI levels are better screening tools for illnesses, and for cognitive declines. In fact, a Google Scholar search of “ffmi vs. BMI” leads to a ton of papers that show FFMI is a better tool that BMI, or at the least, as good.
Turning to my own journey, one of the things I’ve discussed in the past is how people tend to look at me and say “Wow, you’ve lost so much weight, you must feel so much better“. And how, unfortunately, I can’t tell them I do. Don’t get me wrong – I feel great. I definitely enjoy physical activity more now (probably because I’ve done a lot of it) and I like the way I look and feel. But I don’t feel way better than I did. In April 2020, I bought a scale that did body fat analysis, and I’ve owned an Omron body fat analyzer since 2011. So I started looking at my old data to see what my FFMI was when I was 415 pounds. Now according to Schutz, Kyle, & Pichard, the 50% range for FFMI for a male caucasian is 18.9 for 18-34 year olds, and 19.2 for 35-54 year olds. Females are slightly lower, in the 15.4 to 15.9 range). 90th percentile is around 20.5 to 21.1. Using these norms, basically you want your FFMI to be above 20 for males, with low body fat (Under 20%), and above 16 for females, with low body fat (e.g., under 25%). (You can calculate your own by looking at this website).
As of today, my FFMI is 21.5, with 13.7% body fat at 193.6 pounds. By all metrics (FFMI, BMI, Body Fat %), I’m in excellent shape. At my heaviest, when I was 415.2 and had around 50% body fat, my FFMI would have been 26.71! So by 1 of the 3 metrics, I was actually healthy and in the extreme top range of FFMI scores.
So what do I take from all of this? To understand if someone is healthy, you want to focus on body fat percentage and FFMI. BMI is a trash metric that isn’t as good as Fat% and FFMI in any way, and in the worst way, it’s down right racist. Sadly there is no one magical number you’ll ever find for someone – weight, BMI, FFMI, Body Fat %, or anything else. But the next time someone tells you that you’re overweight or obese, ask them what criteria they’re using. If it’s just BMI, then perhaps remind them that Athletes don’t depend on BMI alone because if they did, Usain Bolt would be just under “overweight” at a BMI of 24.5, as would many other olympians!