> Ketones being an alternative fuel for the brain My understanding is that the brain / neurons require glucose to operate, they don't directly metabolise keton

> Ketones being an alternative fuel for the brain My understanding is that the brain / neurons require glucose to operate, they don't directly metabolise ketones to a great degree. When in ketosis, blood sugar drops very low and the brain's glucose has to be sourced from gluconeogenesis: an inefficient and minimal conversion of ketones to glucose. This low blood sugar has metabolic effects on neurons (as well as many other types of cell). The USP of a ketogenic diet is that it allows persistent sustainable low blood sugar, which is otherwise only seen in inherently unsustainable fasting.