>Being on an empty stomach also seems to help

There might be microbes (bacteria) in your gut (intestines, etc) that produce toxins that dull your thinking when they have food.

The gut-brain connection do seem to be true on my end.

I am always careful to avoid carbohydrates when I am starting work that is concentration heavy.

I have a similar carbohydrate problem too.

If I have more than a small amount of carbs in one sitting, my mind will get hazy and I'll get really sleepy an hour or so later.

I did a blood test recently and everything was OK, so I'm really not sure what the problem is.

And funny thing is that I don't seem to have this problem with quick sugars. I could have ice cream and chocolate and not crash at all.

Mixing tryptophan heavy foods (chicken / salmon / cheese / nuts) with carbs is gonna make you crash / sleepy.

Same thing with salted + carb heavy food, as the body starts putting on water (dry mouth, drinking loads, puffy + tired)

That's interesting that you mention that. I have ADD and I've taken Adderall for most of my life to treat it. One of Adderall's most common side effects is suppression of the appetite. On the days I don't take it I also feel like I'm able to concentrate way better when I'm dehydrated and my stomach is empty. I've always figured that's just because my body has adjusted to the side effects of Adderall after many years, but I'd be curious if there's any research that associates a lack of gut activity with higher concentration because I feel the exact same as you.

About 70 to 80 percent of the body's immune cells can be found in the gut. I strongly suspect this means eating is the single biggest immune challenge the body deals with in day-to-day life.

I'm the other way. If I'm hungry, I'm thinking about food all the time.

A key for me is to keep snacks on hand that aren't too bad for my health.