> maybe it's placebo but I recognize a stronger ability to focus when I'm in the midst of a fasting period
I vaguely recall a recent study that covered this. I believe the theory is that when we're hungry our brains become more focused to aide in our ability to find food. After we've eaten there's not much need to think.
To the greater arguments regarding intermittent fasting: I hate to call on the historical human argument, because it's often abused (e.g. for the raw food diet, paleo diet, etc), but in this case I think it applies because until very, very recently the vast majority of humans spent most of their lives hungry. Hell, we still have parts of our world today where people starve to death (not because of lack of food production, by the way; it's a political issue). It's no surprise, then, that not only can we go without food just fine, but a significant portion of our behaviors and adaptations are built around intermittent fasting.
That isn't to say that intermittent fasting is maximally optimal. It may just be more optimal then how most Americans eat (large meals 3+ times a day, occasional snacks and a sugary beverage throughout the day).
I think the biggest issue we face today is our food culture, particularly in Western societies. Food is the center of every occasion. In Latin derived families you see the habit of constantly forcing food on guests, and both Latin and Southern European cultures are big on forcing their children to eat until their plate is empty.
This made a lot of sense when food and calories wasn't abundant, and there has likely been a lot of selective pressures on those cultures over our recent history. But food is plentiful now. Whereas in the past when forcing children to eat every last speck meant them barely getting enough to eat; today forcing children to eat, eat, eat means making them fat.
Unfortunately I don't think the same selective pressures will work. Being overweight isn't going to stop you from raising a family. So our only two real solutions are to either forcefully change our cultures so that dieting, whatever the diet may be, is the cultural norm, or we apply science to develop foods with lower caloric densities. The latter is, unfortunately, demonized for some godforsaken reason (e.g. artificial sweeteners).