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Comment by Mountain_Skies | Hacker News Reader

It is my understanding that humans generally are limited to converting about 0.8% of the body fat into usable energy per day. If women generally have more body fat, then they would be able to yield more energy from it before hitting the 0.8% limit (which likely is spread out over the day especially in endurance events). Or there might even be some variance in that 0.8% limit, with women being able to convert a bit more per day than men. This would fly in the face of the conventional wisdom that women have a more difficult time losing weight than men. Certainly would be an interesting possibility to study.

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Well recent studies have actually found that women have a different catabolism than men. Women also switch to catabolism while they still have glycogen remaining in their muscles, meaning they don't build up as much lactic acid.

This flies in the face of conventional wisdom because all of the original studies were only done on men.

Off the top of my head, I'm not sure if women do have a harder time losing weight than men, but I know that a woman's body reacts to starvation differently. That may play a role.

There is a massive need for "foundational" studies to be redone with women. The assumption that men and women have the same metabolism has been shown to be wrong, and it has a lot of broad and overarching implications, especially in the field of medicine.

My layman's understanding is - fat burning results in CO2 - CO2 is only removed by exhaling - we exhale ~about~ 2lbs of CO2 per day - fat burning is limited by the amount we can exhale

note: this does not claim one can only burn 2lbs of fat/day only that resulting CO2 from burning some amount of fat must fit in the exhaling budget

Very interesting. I assumed that the limit was due to some internal process and hadn't considered maximum CO2 output. Wonder if this means people with larger lung capacity could burn more fat per day.

Sounds dubious, source?

Can you specify what you find dubious?

Anyway, here's the source: https://www.ncbi.nlm.nih.gov/pubmed/15615615

It states the maximum conversion is (290+/-25) kJ/kgd. It's been a while since I last worked on this subject but I believe that works out to somewhere in the range of 0.8% to 1% of body fat that can be converted into energy per day at most.

Of course there were some experimental controls in the study that don't always map exactly into the real world. There always are but this should be close enough for the discussion here.

Thanks for the source! Jumping from that study (which is tightly focused) into the statistic of "0.8% body fat per day limit" is dubious, and "close enough" doesn't work with nonlinear systems like the our bodies. Read many of the threads around discussing that article for more information :)

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