4 ms·

Study Suggests Lower Mortality Risk for People Deemed to Be Overweight

17 points by credo 14y ago

kleiba 14y ago
The report on nearly three million people found that those whose B.M.I. ranked them as overweight had less risk of dying than people of normal weight. And while obese people had a greater mortality risk over all, those at the lowest obesity level (B.M.I. of 30 to 34.9) were not more likely to die than normal-weight people. I seriously don't understand this paragraph. Maybe it's because I'm a geek, but I was always under the impression that the risk of dying was 100% no matter which group you belong to. I don't understand what the author of the article is trying to convey here.
- keithwinstein 14y ago
  Most medical studies, including this one, summarize differences in risks by estimating a hazard ratio. A hazard function gives the conditional probability density of having an event at time T, given that no event has occurred at time t < T. (E.g. the probability that a hard drive first fails in its 14937th hour of operation, except that formally speaking we're talking about the probability density of failing not in an hour, but an infinitessimal instant.) A hazard ratio is the ratio of two hazard functions. Just as with hard drives, death is certain (eventually) but we can still prefer a hard drive with MTTF of 5 years vs. one with MTTF of 3 years.
- YokoZar 14y ago
  Without having read this study in detail, other possible things tend to muck up such studies. Suppose you define mortality as "chance of dying within a year" 1) People who start dying (eg by developing cancer) might take more than a year, and generally they lose weight when they do so. So even if obesity caused you to be more likely to get cancer and die, it wouldn't show up in this sort of data. 2) People who weigh less may be otherwise unhealthy for other reasons -- this doesn't imply that gaining weight would benefit them. In this sense weight is an effect of some other cause. 3) We may not be measuring "overweight" correctly -- scale weight is different from BMI which is different from body fat% which is different from body density which is different from body volume which is different from other things closely associated with "weight" (and specifically the stuff you gain/lose by eating)
- sebcat 14y ago
  FWIW, the JAMA article talks about mortality rate.
- AndrewDucker 14y ago
  It's usually the percentage chance of dying over the next year.
twiceaday 14y ago
BMI is not a completely accurate indicator of obesity so I'm not at all surprised they got this mild contradiction. Doubly so because it is an easily-sellable message.
jacques_chester 14y ago
BMI is like KSLOC. It's the shittiest metric of population health we have ... except for all the others. Height and weight is always collected. Blood cholesterol ... yeah, not so much. So unsurprisingly everything is related back to it. Anyhow. I'd be amazed if many of we key-hunters-and-karma-gatherers are in much danger of zooming into the dangerous band at the bottom of the BMI (modulo EDs). So, given that most people are not rocking pro-bodybuilder fat-free mass indexes, the BMI is still better than nothing.
- antihero 14y ago
  Perhaps BMI + body fat + weight able to lift?
tallanvor 14y ago
BMI was never even meant to be an individual indicator of health. It was an attempt to classify larger groups. It also uses the same values for men and women, even though men typically have more muscles than women, raising their BMI. Any individual who relies on BMI to decide whether or not they are overweight is doing it wrong.
- Lost_BiomedE 14y ago
  Agreed. Also, as we age, lower weight is associated with chronic or terminal illness. I haven't opened up the study, but unless they only looked at healthy participants, this will be another large confounding variable.

17 points by credo 14y ago

The report on nearly three million people found that those whose B.M.I. ranked them as overweight had less risk of dying than people of normal weight. And while obese people had a greater mortality risk over all, those at the lowest obesity level (B.M.I. of 30 to 34.9) were not more likely to die than normal-weight people. I seriously don't understand this paragraph. Maybe it's because I'm a geek, but I was always under the impression that the risk of dying was 100% no matter which group you belong to. I don't understand what the author of the article is trying to convey here.

keithwinstein 14y ago
Most medical studies, including this one, summarize differences in risks by estimating a hazard ratio. A hazard function gives the conditional probability density of having an event at time T, given that no event has occurred at time t < T. (E.g. the probability that a hard drive first fails in its 14937th hour of operation, except that formally speaking we're talking about the probability density of failing not in an hour, but an infinitessimal instant.) A hazard ratio is the ratio of two hazard functions. Just as with hard drives, death is certain (eventually) but we can still prefer a hard drive with MTTF of 5 years vs. one with MTTF of 3 years.
YokoZar 14y ago
Without having read this study in detail, other possible things tend to muck up such studies. Suppose you define mortality as "chance of dying within a year" 1) People who start dying (eg by developing cancer) might take more than a year, and generally they lose weight when they do so. So even if obesity caused you to be more likely to get cancer and die, it wouldn't show up in this sort of data. 2) People who weigh less may be otherwise unhealthy for other reasons -- this doesn't imply that gaining weight would benefit them. In this sense weight is an effect of some other cause. 3) We may not be measuring "overweight" correctly -- scale weight is different from BMI which is different from body fat% which is different from body density which is different from body volume which is different from other things closely associated with "weight" (and specifically the stuff you gain/lose by eating)
sebcat 14y ago
FWIW, the JAMA article talks about mortality rate.
AndrewDucker 14y ago
It's usually the percentage chance of dying over the next year.

twiceaday 14y ago

BMI is not a completely accurate indicator of obesity so I'm not at all surprised they got this mild contradiction. Doubly so because it is an easily-sellable message.

jacques_chester 14y ago

BMI is like KSLOC. It's the shittiest metric of population health we have ... except for all the others. Height and weight is always collected. Blood cholesterol ... yeah, not so much. So unsurprisingly everything is related back to it. Anyhow. I'd be amazed if many of we key-hunters-and-karma-gatherers are in much danger of zooming into the dangerous band at the bottom of the BMI (modulo EDs). So, given that most people are not rocking pro-bodybuilder fat-free mass indexes, the BMI is still better than nothing.

antihero 14y ago
Perhaps BMI + body fat + weight able to lift?

tallanvor 14y ago

BMI was never even meant to be an individual indicator of health. It was an attempt to classify larger groups. It also uses the same values for men and women, even though men typically have more muscles than women, raising their BMI. Any individual who relies on BMI to decide whether or not they are overweight is doing it wrong.

Lost_BiomedE 14y ago
Agreed. Also, as we age, lower weight is associated with chronic or terminal illness. I haven't opened up the study, but unless they only looked at healthy participants, this will be another large confounding variable.