Grr there was a paper somewhere about this. The maxbisn't quite the thing you hit, but there is something similar at the end of pregnancy that is basically give birth or die that was metabolism related and a comparison to a marathon runner was made.
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@sheseala Ketosis?
In late pregnancy, the placenta produces placental lactogen (hPL), which helps break fat to provide energy for the fetus. That can lead to the body being unable to use glucose (sugar) for energy use fat instead. Similar to an athelete "hitting the wall," or "bonking", aka ketosis.
@b4cks4w It might be that.
Trying to find the specific paper I read 7 years ago, but finding a lot of related articles instead.
I did just learn that the baby is not the prime caloric load, it's the changes to the mother's body. So this is an interesting rabbit hole.