I don't have sources handy, but IIRC the brain will generally to run on about a 60/40 or 70/30 mix of ketones/glucose, but in some experiment they gave people i

I don't have sources handy, but IIRC the brain will generally to run on about a 60/40 or 70/30 mix of ketones/glucose, but in some experiment they gave people in ketosis a does of insulin to drop their blood sugar to near 0, and they didn't pass out and were otherwise fine.