The first is what I think people in modern society call hunger, because it's the only kind they've experienced. It's a craving for food, or even just a sensation of not being full. We call "not full" "hungry" when they aren't really necessarily the same.
The second kind comes after you've fasted for quite a while. It's difficult to describe if you haven't felt it, but it's sort of like... tightness maybe as if your body is buzzing or something.
("Je hebt trek, honger hadden we tijdens de oorlog")
Appetite is a feeling I would describe more psychological. I'm smelling something delicious and suddenly want to eat it.
It is psycho-physiological addiction. (smell is not psychology, it is physiological). It is like cigarette addiction. But it isn't a physiological need.
Not having eaten for 2-3 days would be hunger.
I'm replying to your post because I get hungry even quicker. I had lunch (rump steak, potatoes) at 1pm and now at 4:30, I'm hungry again. My BMI Is 21, with rather low body fat.
Even with a BMI of 21, you can probably fast for 20-40 days with no irreversible damage, and that feeling you call "hunger" will not be there after the 2nd day.
You do not know what hunger is until you've felt it. I thought I knew what hunger was, until I fasted for 25 days. Then, I actually discovered what hunger is.
The first few days I get hunger pangs around my usual meal times, but they go away soon enough.
Around the fourth day I get the 'real hunger' feeling where it's your whole body aches for food, but the hunger pangs go away. But that had lessened by the end of my fast.
Even if you're not religious I think it's still worth giving fasting a shot, just because it teaches you about hunger. Most people in developed countries will never understand it.
I wonder if this has an under-explored psycho-therapeutic value, actually. When you can't mentally ruminate at all anxieties definitely dissipate. I'd recommend fasting as a way to clear one's head for sure. You can't get any work done, though. You really need a week off alone.
What really stuck out for me was just how much time I was spending each day either planning meals or eating them. Easily four hours a day, including cooking, cleaning, eating, and planning meals with friends.
The social part was not so big a deal for me, but only because there were four of us in our fraternity trying it all together. Plus, well, living in a fraternity and being in college. I didn't need the excuse of a meal to hang out with people.
Lost 8-10kg (I'm an athletic, not large person) and I could barely exit a car when I visited the doctors office. I remember being very tired, but not feverish, so I don't think that factored in.
Regained the weight extremely fast when I started eating again. I remember how that surprised me!
A few years later I went on a diet (lost almost 30 pounds, sadly since regained). I experienced the same effects - I was irritable, and didn't produce my best work. This was probably a contributing factor to my being selected for a layoff.
I do IF (Intermittent Fasting, 24 to 36 hours with water only once a week), and have found that too, but I have also found that as soon as I start eating again, I get quickly tired and warm (like I started a fire inside my body).
I should also mention that I stopped running so hard during this period and took a multivitamin each day. I've fasted for shorter durations and it's amazing how even 2-3 days without food seems to sharpen the mind. You'll feel less sluggish and simply feel more alert.