Here is a little summary to help understand what Ketosis is.
First thing to understand is that our body cannot burn fat until it has burned off 80% of stored glycogen from the carbs we eat. When we restrict carbs to less than around 40g a day, as there is limited fuel from carbs, our body starts making fat its primary fuel source. So we become “fat adapted”. The oxidisation of fat when it is used as a fuel produces ketone bodies and when that happens, we call that “being in ketosis”. Where our body is just burning fat all day, every day.
Ketones provide great and very stable energy to our brains, removing that fog we experience with the highs and lows of blood sugar when we eat regular carb based diets. However, our body is very smart and will produce as much glucose as it needs to survive without any carbs at all. We can live happily without carbs, but not fat and protein.