4 ms·

I wonder if it's BMI per se, or the lack of exercise? While the two are correlated, they are not the same - you can be fat and muscular at the same time. And if

by m0zg 6y ago

I wonder if it's BMI per se, or the lack of exercise? While the two are correlated, they are not the same - you can be fat and muscular at the same time. And if it's just BMI, then through what mechanism it increases the risk.

jasonpeacock 6y ago
"fat and muscular" still means you're fat. Carrying excess fat is indicative of having metabolic syndrome and the many issues associated with that (chronic inflammation, insulin resistance, etc). (I'm ignoring the fact literal BMI is a poor measure and BF% should be used instead to properly account for the vast variety of body shapes and sizes which have healthy BF% but don't align with the very out-of-date BMI charts & studies.)
- fpoling 6y ago
  BF% is hard to measure. Different manufacturers use different models to map resistivity data to BF%, so for the same person one can get rather different answers.
  - dogma1138 6y ago
    Resistance based measurements are pretty poor especially with only 2-4 points of contact, the accurate ones are displacement based like bodypod and X-ray based. I’m actually surprised that this isn’t something that people have thrown ML at yet, it seems like a problem that an IR camera with 360 degree body imaging and a good model might actually be able to solve.
  - jasonpeacock 6y ago
    Agreed, resistance measurements are not great. At the minimum, you need a friend to use calipers on you, and take those measurements over time to see trending and averages. Even better is a dunk tank or Dexascan to get actual numbers from direct readings, most cities/universities have such facilities but not as accessible to everyone. In a perfect world it would be part of your annual physical, but they still use BMI charts :(
  - nradov 6y ago
    DXA scans are accurate to within 1% and are now available in most urban areas for about $50.
    - brewdad 6y ago
      So about $250 with insurance.
      - nradov 6y ago
        No those aren't generally covered by insurance. You just pay the test company $50.
Scaevolus 6y ago
Muscle mass alone isn't enough. Obese people have far less aerobic headroom (lower VO2_max per kg), so viral pneumonia that decreases their lung efficiency even further is harder to survive. There are many factors: "Fat in the abdomen pushes up on the diaphragm, causing that large muscle, which lies below the chest cavity, to impinge on the lungs and restrict airflow." "the blood of people with obesity has an increased tendency to clot—an especially grave risk during an infection that, when severe, independently peppers the small vessels of the lungs with clots" "Immunity also weakens in people with obesity, in part because fat cells infiltrate the organs where immune cells are produced and stored" "people with obesity also suffer from chronic, low-grade inflammation... Those effects may compound the runaway cytokine activity that characterizes severe COVID-19" https://www.sciencemag.org/news/2020/09/why-covid-19-more-deadly-people-obesity-even-if-theyre-young https://www.sciencemag.org/news/2020/09/why-covid-19-more-de...
- skywhopper 6y ago
  BMI says nothing about fat percentage.
  - Scaevolus 6y ago
    It's an incredibly strong correlation. Very few people with BMI over 30 have under 30% body fat: https://www.researchgate.net/figure/BMI-versus-total-body-fat-percentage-based-on-muscle-mass-status-and-age-Graphs-show_fig1_324466220 https://www.researchgate.net/figure/BMI-versus-total-body-fa... There are some exceptions like professional bodybuilders (often with the aid of steroids), but we're talking about reasons why mortality rates are linked to BMI, not declaring absolutes.
    - im3w1l 6y ago
      I agree with you, just want to say I think the reason skywhooper is bringing it up is "you get what you measure" and that hard rules about BMI risks harming and disincentivizing the body building community.
projektfu 6y ago
You’d have to design a prospective study to find out because most patients are going to lack good data on exercise frequency and type, whereas BMI is directly available from almost every medical record. Therefore you’d need to be asking for the information you want.
DoreenMichele 6y ago
This is a better question than it may seem. Research suggesting lack of muscle may matter more than presence of fat for insulin resistance, among other things: https://news.ycombinator.com/item?id=8748147 https://news.ycombinator.com/item?id=8748147 As noted by others, BMI isn't strictly synonymous with fat. The military tape tests body builders who can't meet weight to prove they aren't actually fat. When my husband was a military recruiter, every year some civilian organization told them they were "overweight." They all had to pass PT tests and meet weight to remain in the military. Muscle weighs more than fat.

by m0zg 6y ago

jasonpeacock 6y ago

"fat and muscular" still means you're fat. Carrying excess fat is indicative of having metabolic syndrome and the many issues associated with that (chronic inflammation, insulin resistance, etc). (I'm ignoring the fact literal BMI is a poor measure and BF% should be used instead to properly account for the vast variety of body shapes and sizes which have healthy BF% but don't align with the very out-of-date BMI charts & studies.)

fpoling 6y ago
BF% is hard to measure. Different manufacturers use different models to map resistivity data to BF%, so for the same person one can get rather different answers.
- dogma1138 6y ago
  Resistance based measurements are pretty poor especially with only 2-4 points of contact, the accurate ones are displacement based like bodypod and X-ray based. I’m actually surprised that this isn’t something that people have thrown ML at yet, it seems like a problem that an IR camera with 360 degree body imaging and a good model might actually be able to solve.
- jasonpeacock 6y ago
  Agreed, resistance measurements are not great. At the minimum, you need a friend to use calipers on you, and take those measurements over time to see trending and averages. Even better is a dunk tank or Dexascan to get actual numbers from direct readings, most cities/universities have such facilities but not as accessible to everyone. In a perfect world it would be part of your annual physical, but they still use BMI charts :(
- nradov 6y ago
  DXA scans are accurate to within 1% and are now available in most urban areas for about $50.
  - brewdad 6y ago
    So about $250 with insurance.
    - nradov 6y ago
      No those aren't generally covered by insurance. You just pay the test company $50.

Scaevolus 6y ago

Muscle mass alone isn't enough. Obese people have far less aerobic headroom (lower VO2_max per kg), so viral pneumonia that decreases their lung efficiency even further is harder to survive. There are many factors: "Fat in the abdomen pushes up on the diaphragm, causing that large muscle, which lies below the chest cavity, to impinge on the lungs and restrict airflow." "the blood of people with obesity has an increased tendency to clot—an especially grave risk during an infection that, when severe, independently peppers the small vessels of the lungs with clots" "Immunity also weakens in people with obesity, in part because fat cells infiltrate the organs where immune cells are produced and stored" "people with obesity also suffer from chronic, low-grade inflammation... Those effects may compound the runaway cytokine activity that characterizes severe COVID-19" https://www.sciencemag.org/news/2020/09/why-covid-19-more-deadly-people-obesity-even-if-theyre-young https://www.sciencemag.org/news/2020/09/why-covid-19-more-de...

skywhopper 6y ago
BMI says nothing about fat percentage.
- Scaevolus 6y ago
  It's an incredibly strong correlation. Very few people with BMI over 30 have under 30% body fat: https://www.researchgate.net/figure/BMI-versus-total-body-fat-percentage-based-on-muscle-mass-status-and-age-Graphs-show_fig1_324466220 https://www.researchgate.net/figure/BMI-versus-total-body-fa... There are some exceptions like professional bodybuilders (often with the aid of steroids), but we're talking about reasons why mortality rates are linked to BMI, not declaring absolutes.
  - im3w1l 6y ago
    I agree with you, just want to say I think the reason skywhooper is bringing it up is "you get what you measure" and that hard rules about BMI risks harming and disincentivizing the body building community.

projektfu 6y ago

You’d have to design a prospective study to find out because most patients are going to lack good data on exercise frequency and type, whereas BMI is directly available from almost every medical record. Therefore you’d need to be asking for the information you want.

DoreenMichele 6y ago

This is a better question than it may seem. Research suggesting lack of muscle may matter more than presence of fat for insulin resistance, among other things: https://news.ycombinator.com/item?id=8748147 https://news.ycombinator.com/item?id=8748147 As noted by others, BMI isn't strictly synonymous with fat. The military tape tests body builders who can't meet weight to prove they aren't actually fat. When my husband was a military recruiter, every year some civilian organization told them they were "overweight." They all had to pass PT tests and meet weight to remain in the military. Muscle weighs more than fat.