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Jiro comments on Lifestyle interventions to increase longevity - Less Wrong

122 Post author: RomeoStevens 28 February 2014 06:28AM

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Comment author: Jiro 28 February 2014 03:19:31PM 1 point [-]

Is body mass a good predictor of risk for people who know that they are not in an obvious category where body mass is expected to be a poor predictor? That is, if you exclude the bodybuilders and limit its use to relatively average-appearing people, is body mass then useful?

Comment author: Lumifer 28 February 2014 08:37:59PM 6 points [-]

Is body mass a good predictor of risk

BMI is a horrible metric that was never intended to be used for evaluations of individuals (it was supposed to be used for evaluation and comparison of whole populations), is known to scale wrongly with height and basically should just be ignored.

Comment author: [deleted] 02 March 2014 03:23:05PM 1 point [-]

While you are technically correct, that shouldn't function as an excuse to let oneself get overweight. My BMI was just measured a couple weeks ago to be 23.7 (between 18 and 25 is "normal"), and even after you account for the fact that I carry some muscle thanks to a year of strength training, I'm still visibly chubby and the nurse told me to lose weight. I agree with her on this.

Comment author: Creutzer 02 March 2014 03:28:26PM 5 points [-]

But what you're doing is exactly ignoring the BMI: the BMI is supposed to be normal, but you think you should lose weight.

Comment author: [deleted] 02 March 2014 04:22:06PM 1 point [-]

Yes, that's my point. However, I'm abnormal: the most common use of ignoring BMI is to let oneself remain overweight against the evidence of its health detriments.

Comment author: Lumifer 03 March 2014 04:24:55PM 0 points [-]

While you are technically correct, that shouldn't function as an excuse to let oneself get overweight.

That's a non sequitur.

To quote you from another post

the most common use of ignoring BMI is to let oneself remain overweight

You don't know that. Asserting an opinion and describing reality are two different things.

Comment author: [deleted] 03 March 2014 04:35:00PM 1 point [-]

You don't know that.

I have not run a statistically significant experiment, no, but I have simpler never heard of anyone even ignoring their BMI when it's a reason to eat more and exercise less. You could say that I have more than a completely baseless prior but less than a completely well-evidenced posterior.

Comment author: Lumifer 03 March 2014 04:58:45PM 1 point [-]

I have simpler never heard of anyone even ignoring their BMI when it's a reason to eat more and exercise less.

Huh? You're making no sense.

The great majority of people ignore their BMI because they don't care. A notable number ignores their BMI because they have better metrics. I ignore my BMI because I think that it's a silly number that tells me nothing that I don't already know.

Comment author: brazil84 07 March 2014 11:39:51PM 1 point [-]

BMI is a horrible metric

I recall reading that BMI correctly predicts obesity in 95% of men and 99% of women. Do you disagree with this?

Comment author: ephion 28 February 2014 04:15:36PM 2 points [-]

The best metrics are body fat percentage or fat-free mass index.

For what it's worth, even vaguely muscular people are going to blow apart the BMI scale. I'm 5'10" and 190lbs at around 13% body fat. My normal weight range according to BMI is 130-173lbs. If I got down to that without losing any muscle mass, I'd be 5% body fat, which is severely underweight. I was completely sedentary before weight training, and I've only been training powerlifting for 1.5 years with moderate results (ie, I'm not quite as strong as most high school football players).

Comment author: RomeoStevens 01 March 2014 01:13:44AM 2 points [-]

even vaguely muscular people are going to blow apart the BMI scale

I disagree, it's fairly hard for people to get much above BMI of 28 while lean. You are likely underestimating your BF, have you done a bod pod or other immersion test?

Comment author: ephion 03 March 2014 03:05:37PM 1 point [-]

I haven't. I use calipers and visual estimation compared to DEXA confirmed images. Calipers, if taken at face value, report me to be at 8-10% BF which is definitely too low. Visually, I currently look like pictures of guys in the 13-15% range, so I add 5% to the calculated result. Even at 16% BF (the highest estimate I can get), I'd be around 7% BF with a BMI of 24.8. That's underfat yet very close to overweight.

Comment author: brazil84 07 March 2014 11:37:38PM 0 points [-]

Would you mind posting a self-pic?

Comment author: RomeoStevens 03 March 2014 07:57:45PM 0 points [-]

ah, you sound more than just vaguely muscular then ;)

Comment author: waveman 19 March 2014 05:09:03AM 0 points [-]

The best metrics are body fat percentage or fat-free mass index.

Do you have a comparison study which included hip/waist as well as body fat percentage?

I have some doubt that your claim is true because the distribution of the fat seems to be very important eg fat around the hips is far less damaging than fat around the abdomen.

Comment author: brazil84 07 March 2014 11:37:34PM 0 points [-]

For what it may be worth, I am "vaguely muscular" and my BMI of 23.6 seems about right in terms of assessing my level of overweight.. I do agree that muscularity can foul up the BMI scale but I think it take more than just modest muscularity to do so.

Comment author: brazil84 07 March 2014 11:32:39PM 0 points [-]

Is body mass a good predictor of risk for people who know that they are not in an obvious category where body mass is expected to be a poor predictor? That is, if you exclude the bodybuilders and limit its use to relatively average-appearing people, is body mass then useful?

I recall reading that BMI correctly assesses obesity in 99% of women and 95% of men. I can try to dig up a reference for this if you like. So the answer to your question would seem to be "yes."