With IM I don't really get to that energetic sweet spot.
It's more like 24h+ into the fast than in the 16-20 range.
That's when you're still somewhat hungry.
Cooking after some 30 hours of fasting is amazing. Everything smells fucking amazing and makes you salivate. People go in for healthy diets usually I think but I just feast.
One time made this amazing deer bolognese sauce, simmered it for ages. Spaghetti, fresh parmeesian (hehe) and a salad of nice fresh tomatoes and some other goodies. A nice beer on top of that.
Mmmm-mmmm-mmm.
Got to do that at home though, since usually that slaps the digestive tract awake and I have to run to the bathroom.
Hyponatremia ends up killing marathon runners pretty commonly, more often than heart attacks but to be fair I wouldn't expect marathon runners to have a lot of the associated risk factors.
It's easy to avoid though. Simply put a few grains of salt into your water.
In the army, as a supply-core nco, that was a must, especially in the summer. A spoon of salt for every jug. I'm gonna refrain from putting the ratios here, because I don't want anyone to go necking salt because of me. Normally we get enough salt from food, so I'm afraid of some trendy would-be healthy kids starting to add a bunch of salt into their water bottles even when they don't do any sweating, thinking it's healthy for them.