For example, although I can remember few actual instances of anyone telling me to "clean my plate" it was always an unspoken expectation that there wouldn't be any food left on the flatware at the end of the meal. I don't know why it never occurred to me to just stop eating when I was full. But it didn't. I just plowed on through, no matter how my stomach felt.
I've been thinking recently about what messages I was receiving from my environment that made me believe so unquestioningly in the "clean plate" idea.

First, there is the worry of being ungrateful for the food we have. When I was a kid Ethiopia was famous for its starvation problems, and I distinctly remember the old standby "there are starving kids in Ethiopia who'd love to have that much food." Starvation is a terrible thing, but obesity isn't much better. There's no cosmic balance of hungriness, it's not as if stuffing an American kid to the gills will somehow alleviate the suffering of a malnourished Ethiopian. But to leave some extra food on the plate was like a slap in the face of a starving kid. There's a happy medium where we can be grateful for the bounty we have while eating just enough to keep us healthy and active.
Next was the idea that uneaten food was an unconscionable waste of money. This seems like a holdover from the days before modern farming hadn't made food ubiquitous and cheap. It's especially on display in restaurant settings. The percent of our budget we spend on food is lower than ever before, yet people seem to think throwing away uneaten food is going to break the bank. While we should cut waste wherever possible, it doesn't make much sense to "save money" by sacrificing your waistline (and piling on a bunch of weight related disease costs later in life).
And then there is the feeling that not eating everything on the plate is a kind of insult to the person who made it. Maybe this is just because I'm too sensitive, but I noticed early that eating everything offered to me plus seconds made the cook extremely happy. Picture "Well, you must really have liked it!" said with a grin spreading across the face. I often ate more than I really wanted just to make sure the preparer knew how much I appreciated it. We need to reorient ourselves to the idea that quality food enjoyed slowly and with care is the greatest complement to the chef. Shoveling it down and asking for more with your mouth full certainly has a dramatic effect but it'll catch up to you in the long run.
Finally, there is the biggest misconception, that eating a lot of food makes you more robust. We even have the phrase, "he's a healthy eater" when we want to communicate that someone eats a lot. Again I think this is a remnant from a time when abundant food was the exception and not the norm. Eating more calories than you consume in a day is not being a healthy eater, it's being an unbalanced eater who doesn't have a handle on their nutritional needs. Especially as a kid, I was encouraged to fill all the way up because to do so was a sign that I was a healthy boy, it made the people around me proud. As childish as it may seem, these first impressions stick with people far longer than they realize.
So what's the alternative, especially for parents trying to feed their brood?
First, I'd start by jettisoning the idea that a human being eats a certain total of food every day. The human body is an impossibly complicated system, and it will require different amounts of nourishment each day. Especially kids who go through periods of high caloric intake to power a growth spurt and then just as suddenly taper off and need to eat less. The body is custom made to respond to changes activity, stress, even weather. We need to learn to listen to our stomach, not our preconceptions of what three square meals a day looks like.
Similarly, we need to embrace the concept that you can be fully nourished and not yet "full". It takes a little practice, but anyone can learn to find that point in an eating session when they are satisfied but not full. We have the image of a truly good culinary experience being one in which we push back from the table, loosen our belts, and say "now that was a meal!" Actually, you've just put your internal organs through a system shock and will feel lethargic for hours. That's not eating, it's gorging. There's another way, and it's taking the time to enjoy each flavorful bite, and standing up from the table feeling light and upbeat, saying "that was a great meal, and now I'm ready to get on with my life!" No more food comas!
The easiest way to facilitate this more natural relationship to our portions is to let our family and children serve themselves, and switch the emphasis from "Eat as much as you want, we've got more in the back!" to "Don't worry about eating it all, it'll keep for a few days in the fridge."
Now I know a lot of this is head-slappingly obvious and you're probably already doing many of these things. The point is that, when I was growing up, no one ever told me this stuff. I really had no idea you could step away from the table at a time of your choosing, not when you finished a marathon of whatever portions had been allotted for the meal. Not until I was already way behind in the fitness department
So even if it seems stupid, find a young person in your life and tell them, "There's no need to clean your plate, just eat until you feel satisfied."
And model that behavior. That's all kids pay attention to anyway.
