As someone who can easily eat 4000 calories of real food in a single meal before feeling satiated, I have found that the fix for me is psychological and behavioral. I have an internalized belief that unless I carry on eating until I feel satisfied, then I will feel hungry and uncomfortable after the meal. However, this is not actually true - if I instead eat a reasonable sized portion for my height and activity level, then wait an hour, I do feel satisfied and comfortable. So the trick for me has just been mentally challenging that internalized belief that I need to eat until I feel full. If I just eat, stop, and wait, I feel great.
"who can easily eat 4000 calories of real food in a single meal"
"4000 calories" ? With "real food" ? In one meal -- how ? I eat 3 full meals and a weight gain smoothie and barely pass 2700 calories for the day. Is there something you would recommend adding to my diet so I can increase my calories a bit as I would like to gain some weight. But seriously unless your meal is 100% deep fried, I can't even picture a 4000 calorie meal.
There isn't one particular ingredient, it's just large amounts of high-fat meat with large amounts of high-fat, high-carb side dishes. Say, skin-on chicken thighs with mashed potato that't full of butter and caramelized onion that's full of oil. It might be hard to "picture" because you're trying to picture a plate of food, but in the volumes I used to eat, the amount of food wouldn't fit on a single plate, even piled high on a large one.
I once ate a deep dish meatlovers pizza that was 6000. I wasn't even full later. Fat is the missing ingredient. The GOMAD diet will put on pounds unless you are lactose intolerant or allergic to milk protein. Eat exactly what you would otherwise, but also drink a gallon of whole milk over the course of the day. If that seems extreme, double or triple the olive oil on your salad. Drench your pasta in ghee or coconut oil. If your smoothie doesn't have some sort of fat or oil it isn't a weight gain smoothie.
There is an Okinawan principle to eating that says to eat until 80% full. There is a lag between actually being full and your brain realizing you're full. I can't find actual papers about it but if you look up Hara Hachi Bu you can find a ton of pulpy news articles about it.
Edit: I have the same problem. I ate a whole frozen pizza a few days ago and felt like crap for a day afterward. Not just a little personal one either. A full Screamin' Sicilian pepperoni...
