It’s a complex system of cellular receptors and substances that activate them, and the receptors can become upregulated and downregulated. Histamine is also a pro-inflammatory substance.
I do better with my insomnia and autoimmune disorders if I am… attentive towards carbohydrate intake. Less sugar is better, slower carbohydrates are better. (I can reliably induce an insomnia awakening at precisely 05:30 by eating dessert after dinner. I’m not yet sure why or how exactly, but the histamine connection makes sense. It also has to do with cortisol I believe.) However, I am also more alert and sharp if I get enough carbs – including sugar. At the right time of day.
Here’s my source for histamine being involved in glucose metabolism: Histamine metabolism in diabetes mellitus and vascular disease, dr. Dalvir Gill’s 1991 PhD thesis: https://discovery.ucl.ac.uk/id/eprint/10120875/
Regarding histamine as an alertness neurotransmitter, I point to early antihistamine medication being sedative. This is because early antihistamines were molecules small enough to cross the blood-brain barrier. Histamine receptors in the brain regulate alertness. As well as the hunger response, interestingly. Old allergy meds make you hungry and then you pass out.
Ketone salts are ok but ketone esters are fantastic.
People that understand how ketosis effects the brain will understand why this works.
There are days that I KNOW I won't have time to eat, and those days I either fast completely or I start my day with a (Bulk.com - not affiliated) hydrobeef protein shake (2 scoops). Those days I feel steadily energized 8am-8pm as if I've had 2 espressos.
I find it all to be in the food. I remember listening on Huberman Lab that caffeine doesn't give you energy, it merely 'blocks fatigue' (which means fatigue is still there - just suppressed).
Decent sleep and food that doesn't hurt you is the only way to thrive.
About six years ago I changed my diet and started Keto. Now that I'm keto-adapted I drink a cup of green tea each morning more out of habit than necessity. Sometimes I need a little 15-minute nap in the afternoon but otherwise I'm good. On a recent 5-day trip I had no caffeine at all and didn't miss a beat.
So, for people who say they need caffeine to get through their day I say, take a look at what you're eating. You might be surprised at how it's slowing you down.
n.b., I'm not saying everyone must do keto. That's just what worked for me. I'm convinced after six years of researching nutrition that eating real[1], idealy organic food and moving their body on a regular basis is all anyone needs to generally stay healthy and have energy.
1: If you look at the ingredients of the food you're about to eat and you can't find them in your kitchen, then it's not real food.