I wonder, though, if there is something in ‘some’ people where they abruptly deplete their glucose in some fashion, have few ketones available, and end up with a migraine (low magnesium in combo with that?). For example I have a friend who gets migraines on occasion, and one other factor about him is a bizarrely high pain tolerance. To the point it’s dangerous for him. It makes me wonder if most people when they “start getting low” on glucose naturally eat something high-energy fast-digesting immediately just by instinct, but he can suffer all sorts of stuff and not even notice, so maybe he’s not reacting fast enough. Most people don’t get migraines of course, but maybe for the tiny subset who do, a few factors like that combine to the perfect storm.
My migraines are salt-related, so magnesium also makes sense. I don’t seem to progress from the aura to a headache on keto, but I do get auras if I don’t get enough salt. And the auras are debilitating enough. Last time I had a full-blown migraine I was in bed for a day and a half.
I’m sure activity has a large part to play in the keto threshold, since intense exercise is inherently ketogenic. With enough of it, as much as 100 grams could be ketosis compatible.