I think the implication isn't that "it was believed", but that it was actually so. In the past, to overeat at one meal, you'd have to go for seconds, or overload a plate. This would be seen as gluttonous. So there would be a realization you ate too much this one time (subconscious, because conscious observations are easy to rationalize away), and then you'd eat less later. Packaged products are perceived as being "serving size", so as the size of the package grows, we're more likely to eat all of it, and not compensate for it later, because you're just eating a "normal" size. There is certainly some psychological trickery there, and because the profits on increased sizes grow faster than the cost to provide them, manufacturers/restaurants directly benefit from this behavior. But, being the rational beings with willpower that we are, we know engineered foods are much more calorie dense than traditional foods, and we should make a conscious decision to limit their intake, and to compensate appropriately when we do eat them. This is where 'intuitive eating" breaks down, because our brain is so easy to fool, and of course "intuitive eaters" abhor calorie counting. For obvious reasons; it's just used as an excuse by fat people to give themselves permission to stuff their faces with junk. If you "intuitively eat" junk and processed food, you will get fat, and that's as much a scientific fact as that fat comes from excess calories.