I think you show that the intervention you're interested in performs not just above a passive control, but above an active control that may itself plausibly have an impact. So rather than a control that does nothing, you have a control group that does some other intervention. Of course there's still pitfalls, but my understanding is that trials showing positive effects vs. "active control" groups are often considered stronger evidence.
I'm dieting at the moment (mainly trimming down after Christmas, and making some room for a winter bulk routine).
Quite a few times, I've been so hungry that it interfered with my thinking. I had to eat something to get my focus back. Currently sub-10% body fat and a pretty seasoned dieter, so I think I have a fairly good feeling for what's real "hunger" and what's just "craving food".
In 2 weeks I'll switch to a weekly 36 hour fast, but I have no idea how I'm going to deal with the hunger pangs affecting concentration. Maybe, as you say, it is something you can train yourself out of.
When you feel that way, it's because your blood sugar is low - your body i quite literally out of fuel. Once you adapt to not constantly providing an easy source of carbohydrates, it will activate other metabolic pathways. That's when you can go for an extended period without food.
If you want a softer landing, I recommend the 16+8 fasting for a week before diving into multi day fasting. You eat at the latest at 20 (8pm), and not until 12 (12am) the next day. It will take some adapting, but it's better than the headache inducing "withdrawals" you'll feel jumping headfirst into 36h fasting.
