Thread by @fioraesoterica

saw an interesting hypothesis the other day and vaguely wondering how much water it holds

the idea is basically:

1) according to sci-hub.tw/10.1016/j.jtbi… and other sources, there is a real-world maximum rate of free fatty acid liberation from adipose tissue

2) in a wide slice of typical humans, this rate may be *significantly lower* than the basal metabolic rate

3) the idea: perhaps the BMR decrease in response to starvation/fasting is a *consequence* of this rate limit rather than an endocrine regulatory choice?

the idea is suggested as an explanation for why some people find it much easier to fast (e.g. for intermittent fasting) than others: if your BMR is dramatically higher than your max stored fatty acid liberation rate, your brain is going to scream at you as your body shuts down

by the way, regular reminder to not go running around assuming that any particular metabolic choice that *your* body is capable of is one that everyone else's can do too

the details of the heat engines we call "humans" are still far too poorly understood to make such generalizations

actually, a fun example:

i was talking with a friend who has a very different metabolism from me. we concluded they literally had no conception of what i would describe as "hunger pains" and had never experienced it in their life.

which one of us is "normal"? does it matter?

their grandfather has eaten ~800cal/day for years, finds it difficult to eat more than that, and does not experience hunger (AT ALL) as a physical sensation. he is healthy for his age according to every test and measurement

i know this is my usual ADHD topic-rollercoaster, but my brain always brings me back to the example of FTO (en.wikipedia.org/wiki/FTO_gene), which has a single SNP that dramatically affects average calorie intake, but the current hypothesis is that it actually affects *homeoboxes*

homeoboxes are basically mini-genes responsible for body layout (see en.wikipedia.org/wiki/Evolution…). they're the things that, if you mix them up, you'll get a fruit fly with arms in the leg slots

but why this strikes me as particularly interesting is that it means there are developmental choices made in early embryonic stages that significantly affect calorie intake later, seemingly independent of all other factors

a (hypothetical) mechanism might be differential treatment of nerve signals by the spinal cord, for example.