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BMI is highly useful. That it doesn't work for Dwayne Johnson is merely an attempt to reject the whole of it because known edge cases don't work. We know wher

BMI is highly useful. That it doesn't work for Dwayne Johnson is merely an attempt to reject the whole of it because known edge cases don't work. We know where it doesn't work: extreme heights and serious athletes who are enough standard deviations of muscle mass outside the norm. For that, we can do body fat %. But body fat% is harder to measure, so we've got a quick yardstick: It is BMI. BMI is rejected because it tells people they're obese and since its unhealthy, they need to change themselves. Noone likes hearing that. The truth hurts. You'll see these common rejections: 1. Bodyfat loss is hard, so its claimed as not a good measure. 2. BMI has outliers so _mine_ being bad doesn't count. 3. Because not being obese does not provide data about health, they attempt to deny obesity as a poor health marker. This is almost always "you can't tell a skinny person is unhealthy" retort as an excuse to reject obesity as unhealthy. They will not escape the evidence-based scientific truth that obesity is unhealthy.

soperj 7y ago
I'm 5'11 and 185. I'm in the overweight section of BMI, yet have under 10% bodyfat. I'm definitely not an elite athlete. I used to play hockey at a junior level, but now just bike to and from work. Every thing during my physical is in a good to great range. No issues what so ever. Yet BMI says I'm overweight. To me that's an issue with the index.
- nradov 7y ago
  Which technique did you use to measure body fat percentage?
  - soperj 7y ago
    A scale that sends electrical impulses through the body (at least that's what i was told it does)
    - nradov 7y ago
      Those electrical scales only give a general indication and are not calibrated to be clinically accurate. I have one myself and it fluctuates up and down significantly day to day. So it's basically just a fun toy, not a true medical device. You shouldn't cite such unreliable numbers to try and make a point here.
      - mcphage 7y ago
        > You shouldn't cite such unreliable numbers to try and make a point here. Isn’t this entire conversation about unreliable indices?
    - AjithAntony 7y ago
      I stepped on one that told me I was 13% fat. Which is ridiculous. Judging by the photo charts of body fat percentage, I'm probably 20%
- kevin_b_er 7y ago
  You have a body fat percentage that should result in a well defined 6-pack and you're barely into the overweight category. You've successfully double-checked by doing a body fat percentage measurement. BMI was still a good and fast check with minimal cost.
- ericmcer 7y ago
  To get those #s you would need to have an extreme diet/exercise regime. 185 at 5’11 is either a lot of extra fat or muscle. If you are Sub 10% you definitely have a super defined 8 pack and some of that weird muscle striation body builders get. Would be very surprised if you achieved that by just biking to work.
  - soperj 7y ago
    I have large legs (around) from all the skating growing up. Don't have a defined 8 pack, never really had a strong core, it's mostly legs.
    - ericmcer 7y ago
      To Quote Mens Health: "The 7% guy is definitely following a very strict regimen,” he explains. He’s probably eliminating certain macronutrients, like being Paleo with no carbs, and is definitely paying very close attention to what he eats. Meanwhile the 10 to 12% guy is in constant flux—some weeks he’s at 9 percent, others he’s at 12%. “He might have a cheat meal—splurging on wings instead of steamed asparagus when out with the guys—but not necessarily a cheat day,” McCall says. Someone at 15% is having a cheat day. “He’s paying attention and making certain decisions—no fried foods, burger without the bun, no accidental break room pastries. But he’s not uber health conscious,” he adds."
m463 7y ago
Rules of thumb are useful, as long as you understand their limitations. BMI requires simple passive equipment to measure, the subject doesn't really have to participate and the subject is not at risk. But it really can be misleading and counter-productive when you start exercising when fat is replaced by muscle. We really need more accurate static measurement devices that don't need to weigh you underwater. Fatbit maybe? :)
- nradov 7y ago
  DXA scans are about as accurate as a hydrostatic test. They do involve a tiny bit of x-ray radiation exposure.
- sixplusone 7y ago
  It's missing at least one dimension to be useful. Maybe factoring in something like height/waist ratio (for men)...
sixplusone 7y ago
BMI is useless for the people who care about fitness the most. It's optimal for those who don't care and needn't worry about it. Then it allows those who are at risk and understand the least to fool themselves.
icosa 7y ago
BMI uses height and weight to estimate body fat % because those were the easiest statistics Quetelet had access to. There's speculation that BMI is effectively a proxy for waist size, given assumptions about body shape (how high the person's waist is) and density (fat to muscle and bone ratio). Waist-circumference-to-height ratio is a proven predictor of cardio health, and is only slightly harder to measure than BMI. Waist-to-hip-ratio is another strong predictor for health outcomes, and can flag people with a normal BMI that have an elevated mortality risk.

soperj 7y ago

I'm 5'11 and 185. I'm in the overweight section of BMI, yet have under 10% bodyfat. I'm definitely not an elite athlete. I used to play hockey at a junior level, but now just bike to and from work. Every thing during my physical is in a good to great range. No issues what so ever. Yet BMI says I'm overweight. To me that's an issue with the index.

nradov 7y ago
Which technique did you use to measure body fat percentage?
- soperj 7y ago
  A scale that sends electrical impulses through the body (at least that's what i was told it does)
  - nradov 7y ago
    Those electrical scales only give a general indication and are not calibrated to be clinically accurate. I have one myself and it fluctuates up and down significantly day to day. So it's basically just a fun toy, not a true medical device. You shouldn't cite such unreliable numbers to try and make a point here.
    - mcphage 7y ago
      > You shouldn't cite such unreliable numbers to try and make a point here. Isn’t this entire conversation about unreliable indices?
  - AjithAntony 7y ago
    I stepped on one that told me I was 13% fat. Which is ridiculous. Judging by the photo charts of body fat percentage, I'm probably 20%
kevin_b_er 7y ago
You have a body fat percentage that should result in a well defined 6-pack and you're barely into the overweight category. You've successfully double-checked by doing a body fat percentage measurement. BMI was still a good and fast check with minimal cost.
ericmcer 7y ago
To get those #s you would need to have an extreme diet/exercise regime. 185 at 5’11 is either a lot of extra fat or muscle. If you are Sub 10% you definitely have a super defined 8 pack and some of that weird muscle striation body builders get. Would be very surprised if you achieved that by just biking to work.
- soperj 7y ago
  I have large legs (around) from all the skating growing up. Don't have a defined 8 pack, never really had a strong core, it's mostly legs.
  - ericmcer 7y ago
    To Quote Mens Health: "The 7% guy is definitely following a very strict regimen,” he explains. He’s probably eliminating certain macronutrients, like being Paleo with no carbs, and is definitely paying very close attention to what he eats. Meanwhile the 10 to 12% guy is in constant flux—some weeks he’s at 9 percent, others he’s at 12%. “He might have a cheat meal—splurging on wings instead of steamed asparagus when out with the guys—but not necessarily a cheat day,” McCall says. Someone at 15% is having a cheat day. “He’s paying attention and making certain decisions—no fried foods, burger without the bun, no accidental break room pastries. But he’s not uber health conscious,” he adds."

m463 7y ago

Rules of thumb are useful, as long as you understand their limitations. BMI requires simple passive equipment to measure, the subject doesn't really have to participate and the subject is not at risk. But it really can be misleading and counter-productive when you start exercising when fat is replaced by muscle. We really need more accurate static measurement devices that don't need to weigh you underwater. Fatbit maybe? :)

nradov 7y ago
DXA scans are about as accurate as a hydrostatic test. They do involve a tiny bit of x-ray radiation exposure.
sixplusone 7y ago
It's missing at least one dimension to be useful. Maybe factoring in something like height/waist ratio (for men)...

sixplusone 7y ago

BMI is useless for the people who care about fitness the most. It's optimal for those who don't care and needn't worry about it. Then it allows those who are at risk and understand the least to fool themselves.

icosa 7y ago

BMI uses height and weight to estimate body fat % because those were the easiest statistics Quetelet had access to. There's speculation that BMI is effectively a proxy for waist size, given assumptions about body shape (how high the person's waist is) and density (fat to muscle and bone ratio). Waist-circumference-to-height ratio is a proven predictor of cardio health, and is only slightly harder to measure than BMI. Waist-to-hip-ratio is another strong predictor for health outcomes, and can flag people with a normal BMI that have an elevated mortality risk.