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BMI alternative for identifying obesity ‘could prevent misdiagnosis in millions’ (www.theguardian.com)
submitted 19 hours ago by to c/health@lemmy.world
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Combining body mass index with other measurements and tests would lead to better care and outcomes, experts say

An alternative to BMI for diagnosing obesity could prevent misdiagnosis in millions of people worldwide, according to doctors who found it more accurately distinguished healthy people from those with harmful excess body fat.

Medical experts have long considered body mass index a blunt instrument for defining obesity, leading to concerns that substantial numbers of people with excess body fat are missed while others who are healthy are wrongly diagnosed.

The new approach, which combines BMI with other body measurements and organ function tests, suggests BMI alone misses obesity in 5-9% of adults, while wrongly diagnosing the condition in as many as 3%.

“This misclassification can account for tens of millions of people, so the inaccuracy of BMI is a big problem at scale and also for individuals,” said Francisco Rubino, a professor of metabolic and bariatric surgery at King’s College London.

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[–] 11 points 15 hours ago* (5 children)

Any improvement in diagnosis is certainly to be celebrated, but I was surprised to find out that BMI only wrongly diagnosed obesity less than 3% of the time.

Seems like it's already much more accurate than it usually gets credit for.

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  • [–] 5 points 11 hours ago (1 child)

    Yeah, that's a lot more accurate than conventional wisdom seems to suggest.

    If BMI says you're obese, you only have a 3% chance of not actually being obese? That's a pretty accurate diagnostic.

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  • [–] 4 points 14 hours ago (1 child)

    I could be wrong but your wording suggests you're misreading that.

    Article states false positive rate is 3% and false negative is 5-9%

    That's obviously not the same as wrong 3% of the time.

    If we assume even tails then 8-12% of the time BMI incorrectly diagnoses.

    Which is about what I'd expect. BMI is an approximate fit model, the further you get from the mean the less useful it is. If you are more than 1 standard deviation from the height mean you are much more likely to get a false positive (if you're short) or false negative (if you're tall).

    In other words it's a line of best fit that doesn't work for outliers

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  • [–] 6 points 13 hours ago* (last edited 13 hours ago)

    I was specifically referring to the enormous number of people who claim that they've only been diagnosed as obese due to the inaccuracy of BMI as a measure, not the (even larger) number of people who should be diagnosed as obese but aren't.

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  • [–] 2 points 9 hours ago

    I think you're probably conflating obese and 'overweight' in regards to seemingly fit or athletic body types. BMI is still notoriously inaccurate when trying to define regulars at a gym or athletes. It often lables them as overweight due to muscle mass being more dense than body fat. But it's pretty difficult to have that body type and lifestyle but be labeled as obese. For example, at my height I would need to weigh 220lbs to be obese. It's doable considering the 3% figure but unlikly.

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