> From my experience, I think clearest when my body is not busy digesting.

Exactly. Digesting is also kind of a burden to your focus, which is why one should not work directly after eating, especially if it was a heavy meal. But digesting ends at some point, after which you do have excessive energy available. So the point is to know roughly how long each meal will burden your body, and plan accordingly when you will reach a performance-high.

One thing I found quite astounding while fasting is how keen my sense of smell is. I normally don't smell much at all, but while fasting I can smell every restaurant in a 2 mile radius.

I guess it's mostly my brain filtering out "irrelevant data" (the location of food becomes relevant when you're hungry!)

That made me wonder if my other senses might be sharper while hungry too. As hunters, I imagine our ability to plan might also benefit.

Has any research been done on the effects of hunger on cognitive performance?

Do you suffer from allergies/chronic rhinitis by any chance? I have hyposmia because of rhinitis.

But I get the same - go without food for a while and my sense of smell increases until I eat and become satiated.

Now whether it’s related to certain allergens that I eat or the body/senses becoming less sharp I do not know.

Probably worth investigating a bit more, I never really dug deeper into this.

Agreed. When I first started IF so many years ago, it was a shocker how much my sense of smell increased. In the sense of evolutionary biology, it makes sense. If you are hungry, you better be able to find your next food source and maximize every sense you have to get it done.