Yeah, Mindy: bone density and body type (ecto/meso/endomorph) are confounders for BMI reliability as well. I’m only medium height but I’ve always been about 10kg heavier in actuality than what people estimate me to be – I just have heavy bones and dense muscle mass.

That said, I am currently well overweight and not just according to BMI either, as a result of illness and medication side effects combining to make me sedentary (gradually improving). But if anyone tried to say my fat was making me unhealthy I’d point out that they’ve put the cart before the horse – my ill-health is what made me fat.

Significant muscle mass confounds BMI totally as an indicator of adiposity.

Every front row in either code of rugby is technically obese according to the BMI. Of course by other measures of adiposity they have low levels of subcutaneous fat and when their cardiovascular fitness is tested it is superior to most people with a much lower BMI.

BMI is an arbitrary number which has been elevated into this almost holy signifier of health, just because calculating BMI is easy whereas taking other more rigorous measurements of adiposity and actual fitness take time and money.

On a related note, I have noticed that since I’ve lost weight over the last two years, people almost always comment that both I and the Zombie King have really slimmed down. He’s lost a bit of weight, just because I’m cooking with less calorie-dense foods, and so on, but he’s only lost maybe 3% of his body weight or so, whereas I’ve lost more like 33%. It’s more than just politeness to him, too, as they will often keep remarking on it to me when he’s not around. Not that I care, I love my doughy guy and I didn’t lose weight for anyone but myself, but it’s happened a remarkable number of times.

The higher a man’s cardiorespiratory fitness, the less fat he has in his abdominal cavity, Dr Jean-Pierre Despres of Hopital Laval Research Centre in Quebec and colleagues found. The relationship held true regardless of body mass index (BMI), a ratio of weight to height typically used to gauge overweight and obesity.
[...]
High waist circumference combined with high triglyceride levels signal a substantially increased risk of heart disease and diabetes, he explained.

Evidence shows fit people are at reduced risk of heart disease, even though they may be overweight or even obese based on their BMI, Despres and his team note in the Archives of Internal Medicine. At the same time, people of normal weight with bulging bellies risk heart disease.

I note that the emphasis on how “fat people can too be healthy!” does tend to cast fat people who are unhealthy as outsiders and lesser, and that’s still a problem, because they’re still humans deserving dignity. Maybe if we can demolish some of the most pervasive fat-hating myths though the unhealthy fat people will also be subjected to less fat-hatred.

Why that doesn’t happen with women is interesting, but I don’t know why it would be. A friend and I got in the habit of refusing to engage in any talk of weight with our friends many years ago. The fact that we felt it necessary to formulate a policy on that is indicative of how much energy women waste thinking and talking about their efforts to ‘perfect’ their bodies.