BMI = weight(kg)/height(m)2
Now, I'm not mathy. Numbers are not my strong suit. But even I can see that it's a relatively arbitrary formula that does not take into account all the variables which measure health. BMI doesn’t differentiate between muscle and fat, it just takes your weight and height into account. It doesn't measure your overall body fat. Leaving aside the "muscle weighs more than fat" argument, which is mainly applicable for elite athletes, more than the general population, the formula is especially flawed because it doesn't take into account where the fat is stored. And that does make a difference. Belly fat and visceral fat is far worse for your health than the blubber on your butt or under your arms. It's the waist that matters - it's what I mean when I refer to "my gut." So, even if BMI did accurately measure body fat (and it doesn't: it only measures body weight), it still wouldn't tell us accurately how healthy a population or an individual is.
Where it becomes really problematic is when statistics show sharp increases in obesity, and words like "epidemic" and "crisis" start getting thrown around. It's how we've arrived at a point of declaring war on obesity, how fat shaming children has become acceptable, and how screening programs in schools and workplaces seem like a good idea to administrators. What is discussed far less is that BMI category cut-offs got lowered over 10 years ago, so people woke up one day without changing one bit, only to all of a sudden be labelled overweight or obese when the day before they had been normal. This also partly accounts for the sudden increase in “overweight” people, leading to all the hysteria about the Obesity Epidemic (like fatness is somehow contagious). While lifestyles are changing and are more sedentary, when stats are used to back up the “Obesity Crisis” it’s usually traceable back to when they changed the category numbers, making it look like there was a huge spike in fatness.
What's needed is better science, and clarity in statistical analysis. How obese the population is doesn't really tell us how healthy it is, yet decisions are made based on our collective fatness. If the stats helped hospitals to purchase more beds and equipment that fit the morbidly obese, or if the stats helped city planners to include more bike lanes and sidewalks and to limit the number of fast food restaurants in areas around schools, or if the stats supported insurance companies to cover claims which currently are paid out-of-pocket, then I wouldn't be as outraged by the continuous mis-use of the BMI. That's not the case. Instead, the stats are used for headlines to hype up a crisis of epidemic proportions, which people are expected to address on an individual level. Therein lies the blame and shame.
On that individual level, don't worry about your BMI. Worry about your HEALTH. If your doctor or fitness professional uses the BMI and nothing else to determine your weight category, call them out on it. There are far better ways to determine whether you need to lose weight, and how much. Or whether it's affecting your health. "A more reliable, but still relatively simple, assessment of fatness would rely on a skin-fold score based on measurements taken with a caliper at several areas (in men, the thigh, midchest and abdomen, and in women, the thigh, triceps and area above the hip bone) that reflects the amount of fat under the skin. Or, since abdominal fat is more hazardous, simply take a tape measure around the widest part of the abdomen and another at the hips and calculate the waist-to-hip ratio. For men it should be no higher than 0.90, and for women no higher than 0.83." In addition to your waist circumference and body fat percentage, any medical professional should be assessing blood pressure, blood glucose levels, cholesterol, and heart rates.
We simply can't leave our health to an outdated, ineffective formula.
Because, as I keep trying to remind myself, you can't tell how healthy someone is or isn't just by the size of their body.
- Obesity rates: is the BMI a good measurement? (CBC News)
- Nevermind your BMI: to measure your health, it's all about the waist (The Globe and Mail)
- Weight Index doesn't tell the whole truth (The New York Times)
- Top 10 Reasons why the BMI is bogus (NPR)
- The Duh Truck rides again (Shapely Prose / Kate Harding)
- Yes, Virginia, the BMI is BS (Dances with Fat / Ragen Chastain)
- Don't expect government to win the war on obesity (The Globe and Mail)