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BMI fails badly in a variety of use cases. It doesn't handle low-body-fat/high-muscle-mass well at all. But the bigger problem for most of the population is that it has systematic errors for both tall and short people:

 

The formula is KM/H2 (Where K is a constant depending on the units used, M is mass, and H is height.)

 

 A naive look would expect mass to vary with the H3, but body proportions aren't constant with height. The information I've seen indicates that it really should be KM/H5/2 or so. The result is systematic under-reporting of problems for short people and systematic over-reporting of problems for tall people. (Both Carmelo Anthony and LeBron James are "overweight" according to BMI measurements, for example.) Since I've never seen anyone hand-calculating a BMI by the formula, there is precisely no reason not to make the formula more accurate.

 

This is before addressing whether the number for people of typical heights is reasonable. (From what I've seen, it seems that the top of the range is pretty healthy for those folks.)

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OK, after some searching, the last time we did a weight loss support thread was over five years ago.  It didn't seem to make sense to threadomancy that since it is long out of date.  Anyway, I need to

/blows away the dust   So things have happened, jobs were gained and lost, houses moved into and new awesome jobs were gained. Diets failed and exercising failures but something happened.   My ne

welp.   I've done it.   I've lost 50 pounds. 22.7 kilos. All of the weight I gained while on meds for 7 years. It's gone. I'm back down to my college weight.   Not entire

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Yeah, BMI is really a poor rule of thumb. At 6'2" i believe the top of the range was 195 for me. A few years ago i was at 7% body fat and 206 lbs. To get down to 195 i would have been sickly and losing more muscle than i had.

 

So since i am in terrible shape (~360), i should get in on this thread. I'll post relevent stats and goals in the next few days.

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BMI is a statistical tool. If you take the average of a population, and that's overweight, then you have a weight problem in the population. Some people are designed to hold more or less weight, but it should average out to BMI. It was not designed to measure individual fitness.

 

Also, it had some issues with taller than average people and was designed for 19th century Belgium. So there's that too.

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Not to hurt any feelings, but visiting from Europe I can tell you that Americans' perception of what is "normal" with regard to body fat, has shifted tremendously since I first visited in the 90s.

I am one of the biggest guys at my company (office work) and I am obese to the point where I am seeing some pretty serious health issues starting to crop up. I feel normal weight when I visit the US, if not small in some contexts.

Yes BMI is overly simplistic and biased towards classifying people as obese. But we tend to use those around us as mirrors and it affects our perception of what is normal. The statistics do not lie. We are, on average, all getting heavier with every passing year and it is affecting health in very real and measurable ways. BMI is biased towards classifying people as obese, sure. But our concept of "normal" is steadily shifting towards higher and higher body fat percentages. I see a tendency towards rejecting BMI with the argument "it doesn't fit my body type". Well, consider that this is what basically every single one of us obese people tell ourselves. 

For me, I don't really bother too much with BMI. My failing knees are all the indicator I need to tell me things are headed in the wrong direction. Funny enough, looking back at when my knees were happy, it's at the high end of the "normal" BMI range.

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True enough. At 6'1" (185cm) and 202# (91.6 kg) I consider myself overweight. And the top "normal" weight (189#/85.7 kg) is probably about right for my body type. (FWIW, I'm both active - 3,000,000 steps per year, mostly in high-heart-rate exercise - and have a high metabolism - BMR of about 3350 kcal/day.)

 

Which says nothing about BMI's failings for people farther out on the bell curves.

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So about those BMIs...  I really wish there was a better way to calculate appropriate weight.  It's reasonably accurate for me, but I've noticed with my kids that it can be very inaccurate.  I mean, there was a point where it was telling my daughter that she was at the high end of the normal range, but I was having trouble finding clothes to fit her frame because she's so narrow and thin around the waist.  I'm not sure where the weight came from, unless it was her thigh muscles, which are larger than normal from ballet, etc. 

 

So good guideline, but only to a point.  If you have good fitness metrics and a crappy BMI, it's not worth panicking about.  I may have a different perspective after having had a sister with an eating disorder, however. 

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I've never bothered to calculate my own BMI, heck we didn't even own a scale until we bought Wii Fit.  (See above comment about anorexic sister.)  I can tell when I've gained or lost a statistically significant amount of weight.  (About 5 pounds.)  Or perhaps I should say that my clothes will tell me.  ^_^

 

The BMIs I've been given for my kids were either a) calculated by Wii Fit or b) on school fitness progress reports.  Ironically all my kids are pretty fit except the oldest, and he hasn't been a kid by anyone else's standards for several years.  I suspect it's hard to keep up with the height measurements, and obviously with 3 daughters I'm keen to emphasize health rather than foster a skinny=pretty mentality. 

 

I haven't weighed myself all week because I'm on antibiotics.  Tends to bloat me up, plus I need to push more fluids to help my sinuses.  Pedometer says I'm mostly keeping up on step counts, plus Amazon had a random deal on the pedometers so I ordered on for my hubby.  He thinks he walks around a lot at work, but I want him to have a way to track it.  (He's been on about losing weight longer than I have.)  Next week I'll post more results.  ^_^

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Lost 500g at weight watchers weigh in yesterday.  Feeling lousy has helped depress the appetite. 

 

I've even been staying away from the really big buzzies that you catch at the airport.

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I keep thinking that there ought to be a more refined method of calculating ideal weight that involved taking more than one body measurement.

 

I found out today that NFL teams measure hand-size as a stat on QBs and perhaps Wide Receivers.

 

My height measurement changed at some point in the last 15 years. Used to be 76 inches tall; now 74 inches. That happens to adults as they age, but a BMI chart says you ought to shed 10 or 15 pounds to keep your BMI numbers. Height can change like that because of cartilage loss in joints and spinal compression which would not necessarily associate with significant weight drop.

 

But suppose instead of height or in addition to height, wingspan was checked? (Wingspan is middle finger to middle finger with the arms outstretched. Think: Vitruvian man pose.)

 

There ought to be some set of measures that could be done to assess whether somebody has a thick or frail ribcage, extra long legs....narrow shoulders. At a given height, people can differ a lot just based on skeleton. There needs to be a way to index for that.  :mellow:

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In most people, 'wing span' is almost exactly the same as height though.

 

In an older person --who has shrunk a little-- hypothetically, it would preserve their original height.

 

Anecdotally, maybe one person in 30 has a wingspan that differs. (My wingspan is 78 inches; maximum recorded height was 76 inches, currently just 74, maybe 74.5  :upside:  The other 29 kids in my HS Science class all matched up.)

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