In my experience, it seems the brain gets addicted to having a constant flow of glucose streaming into it (it's the most expensive organ to run, calorically) an

In my experience, it seems the brain gets addicted to having a constant flow of glucose streaming into it (it's the most expensive organ to run, calorically) and it gets to think a lot more when it has its fuel. This isn't necessarily healthy, especially if left unchecked for a long period of time. Part of the benefit I believe I've gotten from fasting is re-training my brain to work well in a variety of glucose levels (including very low). These days, I can feel my body switch modes when I enter a low-glucose state. It's a certain type of relaxation that feels like my brain just stops running certain programs. For example, it can't afford to hold on to dramatic, powerful emotions in that low-fuel state, and so it stops running its "replay enraging memories" program, so to speak. You're correct that the brain needs constant fuel, but we have an unbelievable source of fuel in our bodies called fat. Increasing the metabolism's flexibility, such that it can gracefully tap into that massive fuel source, has had a noticeable impact on my mental and physical health. IME, it's more like a hump you have to get over, for what that's worth.