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Comment by bhaney | Hacker News Reader

> Of the participants, 44.5% were overweight, and 49.5% were obese

That was a hard one to figure out. I guess the "overweight" classification here probably means "overweight but not obese" and nearly the entire cohort was overweight in the conventional sense?

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Yep looks like they're non-overlapping. From the article -

> 44.5% (98/220) of the participants were overweight (BMI 23.0-27.5 kg/m2) and 49.5% (109/220) were obese (BMI > 27.5 kg/m2)

25-29.9 is the usual range for “overweight, but not obese” in the US and Germany (so probably the rest of Europe, too); I remember my hotel room scale in Korea showing 23 as the start of overweight, so I guess the ranges in that study are more commonly used across Asia - the study was done on Singaporeans.

Yes, obesity is on a scale for the medical profession. I can’t name all the steps but it’s basically severely underweight, underweight, normal weight, overweight, obese, severely obese. As far as the cohort, sleep apnea is often a side effect of obesity, though not always caused by it (see central apneas which is a nervous system disorder).

Sleep apnea compounds obesity because it makes it difficult to get restful sleep, which is one of the necessary tools for losing weight.

The BMI (Body Mass Index), while far from perfect - mainly because it can't tell the difference between relatively heavy muscle and relatively light (density wise) fat, so a very fit and very strong person can wrongly be classified (and in the opposite direction too) - is still the standard recognised by the WHO, by the NHS in the UK, etc. It's just calculated by body mass divided by the square of the body height, using kg and m.

And then there are specific names for ranges of BMI, which include "Normal range" for 18.5 to 24.9, "Overweight (Pre-obese)" for 25-29.9, and then three classes of "Obese" above 30 as well as three "Underweight" types below 18.5.

Generally this is simplified down to "Underweight", "Normal", "Overweight", and "Obese", with the following words after "Normal" and "Overweight" being implied, and with the multiple levels of underweight and obesity ignored unless discussing someone light or heavy enough that it's worth considering the differences between "Obese (Class I)" and "Obese (Class III)", or between "Underweight (Mild thinness)" and "Underweight (Severe thinness)" - all still based purely on the BMI number.

Sorry for the long winded answer, but even more here: https://en.m.wikipedia.org/wiki/Body_mass_index

Weirdly it seems like this study used the same logic but set non-standard boundaries (27.5 rather than 30 as the point between Overweight and Obese).

> a very fit and very strong person can wrongly be classified (and in the opposite direction too)

Unfortunately, it usually goes in the bad direction, by quite a bit. BMI under-predicts obesity. You only have to hit 25% body fat as a male to be obese, or 32% as a female.

https://academic.oup.com/jes/article/7/Supplement_1/bvad114....

> The BMI (Body Mass Index), while far from perfect - mainly because it can't tell the difference between relatively heavy muscle and relatively light (density wise) fat, so a very fit and very strong person can wrongly be classified

Let's be honest a second here, for every "too muscular bmi obese" there are a thousand "good ol obese"

Interestingly that horseshoe effect of people with large muscle mass having a high bmi might be appropriate for sleep apnea. Strong-men who move in to very high weights (120kg+) will almost always need CPAP due to muscle mass around their necks

The boundaries are different for South Asian and East Asians. NUS's participation probably influenced using the Asian cutoff rather than the Caucasian cutoff.

> and nearly the entire cohort was overweight in the conventional sense?

In this sense, in the US, over 70% of adults are overweight ("overweight or obese"). So the numbers seem reasonable splitting that population in half.

Sleep apnea also affects people with thick necks, such as people who used to play sports or lift heavy things. So you can be a slim, thick necked person and still be affected by it.

This comedian's mom taped him in the middle of sleep apnea - https://www.youtube.com/watch?v=iP1rMGlUCck

Yeah that's probably based on the BMI definition. Overweight is a BMI > 25, and obese is > 30. So yes, nearly the entire cohort was overweight by definition. BMI is a population measure and normal, healthy people can definitely fall into the overweight category. But it's still useful, including when summarizing the participants of a study like this.

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