I'm talking about adults who would normally be busy working, and you wouldn't think their minds would be on food it they were engrossed in what they were doing.
When I am busy working, and my attention is completely focused on what I'm doing, I never think about eating because I am so engrossed in what I am doing. After a significant amount of time (like hours) since a meal, I may suddenly be aware my stomach is nudging me with growls.
Frankly, I think we don't eat enough at our regular meals, cheating ourselves of satisfaction by eating "food lite", then needing something else, even if just for mental fulfillment, to fill us up.
I don't know if it's the amount we eat, or the nutritional composition of what we eat, or both, that determines whether we feel satisfied, and satisfied enough to not think about food until the next real meal.
If I eat just the right balance, for me, of protein, and carbs, and calories, for breakfast, I'm rarely even hungry at lunchtime, and most often don't eat anything again until I crave a mid-afternoon snack or cup of coffee. If I just have the same amount of protein for breakfast, but without enough carbs to boost my calorie intake high enough, I'm going to get hungry sooner, and I'm going to feel less satisfied. The same is true if I have a high carb/high fat breakfast (which is pretty much never) that has plenty of calories (like a donut), but it lacks at least 15 grams of protein, I'm also going to feel hungry sooner, and to feel less satisfied sooner. So, I know I need both a good amount of protein, and sufficient carbs, for both bulk in the tummy and caloric energy, to leave me feeling satisfied and not looking to snack between meals. And I eat the same breakfast every day because I've hit on the perfect food combo for me, and I don't seem to get bored with it.
Why would an otherwise healthy adult, if they ate a good size nutritious breakfast and lunch, even want more than the maybe small little treat in between?
Boredom. That's one reason with me. I definitely snack more when I'm at home and not fully occupied or engrossed with what I'm doing. And the availability of things to snack on is greater when I'm home. So a lot of that kind of snacking, when I'm at home all day, has nothing to do with hunger, it's satisfying some other mental or emotional need. I can eat a perfectly satisfying dinner, but still crave ice cream two hours later because I know it's in the freezer and it tastes so damn good. Or I'll suddenly remember the new cookies I bought yesterday, and I'll want to try one.
Or, if you work in an office, where there are cookies or cake next to the coffee machine, you may take some just because it looks so appealing, and because it's right there and available, even if you hadn't been thinking about eating 5 minutes before, and even if you aren't hungry.
The more we are surrounded by food, particularly visible food, whether it's actual food in whatever environment we're in, or food in TV ads, the more we are prompted to eat and snack and that encourages more "food contacts". Shopping malls tempt people with some kind of food every few feet.
I know it's disastrous for me to go shopping in a supermarket when I'm feeling hungry, like just before dinner time. I buy more "snack" stuff--potato chips, pretzels, cookies, flavored popcorn, etc. than I would at any other time. And then it's available to me when I'm home and bored or whatever. When I'm not hungry when I shop, I buy much less that's not intended for regular meals, and less in the way of junk snacks. But, when I am hungry, the mere sight of certain bags of snacks in the supermarket sets off all sorts of "food contact" needs, and breaks down both will power and judgment on my part, even though those aren't the sorts of things I even want to eat at that moment, because I really do want to go home and eat a real meal, and I do go home and eat a real meal. Go figure.
Food has some mysterious powers.