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> Women might benefit from their higher percentage of body fat since both sexes lose a similar amount of fat during an ultra-endurance performance such as a 100

> Women might benefit from their higher percentage of body fat since both sexes lose a similar amount of fat during an ultra-endurance performance such as a 100 km ultra-marathon (Knechtle et al. 2010a, b, 2012a, b). Sounds like BS to me. Running burns about 100 Calories / mile[0] (62.5 Calories / km). 100 km means 6250 Calories burned. Fat is 9 Calories per gram, so 6250 Calories is 1.5 lbs (0.694 kg) of fat. Even if the calorie burn rate is way off - say by 50%, there is no way any of those athletes is in danger of running out of body fat. And that doesn't even count the carb gels and other food runners typically eat on runs. ___ 0. https://www.runnersworld.com/nutrition-weight-loss/a20784289/the-burning-question/ https://www.runnersworld.com/nutrition-weight-loss/a20784289...

eredengrin 7y ago
> Running burns about 100 Calories / mile[0] (62.5 Calories / km). Okay, at least that blog post is written by someone with a phd, but you can't really take this at face value either. It's probably reasonably true in general (obviously still highly dependent on the person doing the running), but you seem to be assuming that this rate is the same on short runs and long runs, which sound suspicious. I wouldn't at all be surprised if the rate of energy expenditure increased as the time/distance of the race increased. Also if they're running instead of sleeping, I imagine that is probably increasing energy use as well. I'd also be pretty surprised it the 100 calories/mile was taking into account the person's resting metabolic rate. That could easily add another one to two thousand (more depending on the person) calories per day. Finally, even with your analysis coming to 1.5lbs of fat, that's quite a lot of fat in a trained athlete. I'd expect most of the men running these races are well below 10% body fat, and the lower your body fat is the more resistant the body tends to be when it comes to losing more. Losing 1.5 or more lbs of fat would probably be moving their body fat percentages down quite noticeably, which is not easy to do at such low levels. So maybe it is all bs, but I don't think it can be ignored so easily either.
- nordsieck 7y ago
  > I'd expect most of the men running these races are well below 10% body fat You're way off > This study compares body composition characteristics with performance among participants in a 161-km trail ultramarathon. ... Mean (+/-SD) BMI (kg x m(-2)) was 24.8+/-2.7 (range 19.1-32.2) for the men and 21.2+/-2.1 (range 18.1-26.7) for the women. Among the three fastest runners, BMI values ranged from 22.1 to 23.4 for men and 21.5 to 22.9 for women. [0] ___ 0. https://www.ncbi.nlm.nih.gov/pubmed/20222002 https://www.ncbi.nlm.nih.gov/pubmed/20222002
  - atomical 7y ago
    You are confusing BMI with body fat percentage.
    - nordsieck 7y ago
      > You are confusing BMI with body fat percentage. I understand that they are different things. Unless these are bizarrely jacked ultra-marathoners, BMI should work just fine.
      - frickinLasers 7y ago
        For clarity, you could have just quoted the body fat percentages from the next couple sentences in the abstract. >> Mean (+/-SD) percent body fat values for men and women were 17+/-5 (range 5-35) and 21+/-6 (range 10-29) , and ranged from 6 to 14 and 14 to 27 among the fastest three men and women. I would imagine the fastest finishers are not "bizarrely jacked" (they usually look pretty scrawny), but their BMI is not very well correlated with their body fat percentage.
        eredengrin 7y ago
        Also this line > We conclude that despite wide variations in BMI and percent body fat among ultramarathon participants, the faster men have lower percent body fat values than the slower men, and finishers have lower percent body fat values than non-finishers. So I do stand corrected that not all of them are significantly below 10% body fat, but some definitely were (I don't see a breakdown anywhere giving an indication of how many), including some of the top finishers. I'd also imagine the ones at higher percentages who performed well probably have higher floors to begin with for how little body fat they can reasonably reach. In any case, it is not at all abnormal for BMI to have nothing to do with body fat percentage or how jacked someone looks, especially with athletes. BMI is probably one of the most meaningless health metrics in common use.
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sandworm101 7y ago
>> Running burns about 100 Calories Totally depends on the runner. An 85lb female athlete will burn X per km. A 300lb male, covering the same distance/speed, will burn at least 4X and probably 6X.
- atomical 7y ago
  For the sake of their joints I hope a 300 pound male isn't running long distances.
- thatoneuser 7y ago
  Seriously doubt there are 300lb dudes running many ultra marathons. I recently read that book by the ex marine dude who did them. He was a freak in the low-mid 200s and he talks about how he destroyed his body pushing thru it. On top of it runners have sugar and whatnot they eat on the way, so op was making a conservative estimate.
  - 9935c101ab17a66 7y ago
    Are you talking about https://en.wikipedia.org/wiki/David_Goggins https://en.wikipedia.org/wiki/David_Goggins? If so his wikipedia article is fcking hilarious. Someone should coin a term for people who write self-aggrandizing hyperbolic autobiographical wikipedia entries.
    - selestify 7y ago
      Holy shit your comment made me curious about the Wikipedia entry, and boy oh boy were you spot on! Hahahaha
    - p1esk 7y ago
      I was curious so I just read it - even if half of it is true, he’s an incredible individual.
    - topmonk 7y ago
      In what way is it hyperbolic?
thrav 7y ago
The body is sure to put a limit somewhere above zero, and if men are already sub-8% they don’t have much to spare.
robotresearcher 7y ago
Also, women tend to weigh less, so the calories per km is less.
- wallace_f 7y ago
  Yea I doubt body fat is the reason. I bet women's bodies just burn less/km than men's. Not just in weight, but also in anatomy. Not just skeletal structure, but muscle composition, etc.
hollerith 7y ago
You are assuming that a fat cell can deliver into the bloodstream all of its fat over the course of the ultramarathon. If on the other hand it can deliver only a small fraction of its fat in that amount of time, then the argument in grandparent is saved from your criticism.

eredengrin 7y ago

> Running burns about 100 Calories / mile[0] (62.5 Calories / km). Okay, at least that blog post is written by someone with a phd, but you can't really take this at face value either. It's probably reasonably true in general (obviously still highly dependent on the person doing the running), but you seem to be assuming that this rate is the same on short runs and long runs, which sound suspicious. I wouldn't at all be surprised if the rate of energy expenditure increased as the time/distance of the race increased. Also if they're running instead of sleeping, I imagine that is probably increasing energy use as well. I'd also be pretty surprised it the 100 calories/mile was taking into account the person's resting metabolic rate. That could easily add another one to two thousand (more depending on the person) calories per day. Finally, even with your analysis coming to 1.5lbs of fat, that's quite a lot of fat in a trained athlete. I'd expect most of the men running these races are well below 10% body fat, and the lower your body fat is the more resistant the body tends to be when it comes to losing more. Losing 1.5 or more lbs of fat would probably be moving their body fat percentages down quite noticeably, which is not easy to do at such low levels. So maybe it is all bs, but I don't think it can be ignored so easily either.

nordsieck 7y ago
> I'd expect most of the men running these races are well below 10% body fat You're way off > This study compares body composition characteristics with performance among participants in a 161-km trail ultramarathon. ... Mean (+/-SD) BMI (kg x m(-2)) was 24.8+/-2.7 (range 19.1-32.2) for the men and 21.2+/-2.1 (range 18.1-26.7) for the women. Among the three fastest runners, BMI values ranged from 22.1 to 23.4 for men and 21.5 to 22.9 for women. [0] ___ 0. https://www.ncbi.nlm.nih.gov/pubmed/20222002 https://www.ncbi.nlm.nih.gov/pubmed/20222002
- atomical 7y ago
  You are confusing BMI with body fat percentage.
  - nordsieck 7y ago
    > You are confusing BMI with body fat percentage. I understand that they are different things. Unless these are bizarrely jacked ultra-marathoners, BMI should work just fine.
    - frickinLasers 7y ago
      For clarity, you could have just quoted the body fat percentages from the next couple sentences in the abstract. >> Mean (+/-SD) percent body fat values for men and women were 17+/-5 (range 5-35) and 21+/-6 (range 10-29) , and ranged from 6 to 14 and 14 to 27 among the fastest three men and women. I would imagine the fastest finishers are not "bizarrely jacked" (they usually look pretty scrawny), but their BMI is not very well correlated with their body fat percentage.
      - eredengrin 7y ago
        Also this line > We conclude that despite wide variations in BMI and percent body fat among ultramarathon participants, the faster men have lower percent body fat values than the slower men, and finishers have lower percent body fat values than non-finishers. So I do stand corrected that not all of them are significantly below 10% body fat, but some definitely were (I don't see a breakdown anywhere giving an indication of how many), including some of the top finishers. I'd also imagine the ones at higher percentages who performed well probably have higher floors to begin with for how little body fat they can reasonably reach. In any case, it is not at all abnormal for BMI to have nothing to do with body fat percentage or how jacked someone looks, especially with athletes. BMI is probably one of the most meaningless health metrics in common use.
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sandworm101 7y ago

>> Running burns about 100 Calories Totally depends on the runner. An 85lb female athlete will burn X per km. A 300lb male, covering the same distance/speed, will burn at least 4X and probably 6X.

atomical 7y ago
For the sake of their joints I hope a 300 pound male isn't running long distances.
thatoneuser 7y ago
Seriously doubt there are 300lb dudes running many ultra marathons. I recently read that book by the ex marine dude who did them. He was a freak in the low-mid 200s and he talks about how he destroyed his body pushing thru it. On top of it runners have sugar and whatnot they eat on the way, so op was making a conservative estimate.
- 9935c101ab17a66 7y ago
  Are you talking about https://en.wikipedia.org/wiki/David_Goggins https://en.wikipedia.org/wiki/David_Goggins? If so his wikipedia article is fcking hilarious. Someone should coin a term for people who write self-aggrandizing hyperbolic autobiographical wikipedia entries.
  - selestify 7y ago
    Holy shit your comment made me curious about the Wikipedia entry, and boy oh boy were you spot on! Hahahaha
  - p1esk 7y ago
    I was curious so I just read it - even if half of it is true, he’s an incredible individual.
  - topmonk 7y ago
    In what way is it hyperbolic?

thrav 7y ago

The body is sure to put a limit somewhere above zero, and if men are already sub-8% they don’t have much to spare.

robotresearcher 7y ago

Also, women tend to weigh less, so the calories per km is less.

wallace_f 7y ago
Yea I doubt body fat is the reason. I bet women's bodies just burn less/km than men's. Not just in weight, but also in anatomy. Not just skeletal structure, but muscle composition, etc.

hollerith 7y ago

You are assuming that a fat cell can deliver into the bloodstream all of its fat over the course of the ultramarathon. If on the other hand it can deliver only a small fraction of its fat in that amount of time, then the argument in grandparent is saved from your criticism.