> their body's ability to absorb calories is a limiting factor That depends on what "calories" you're consuming (as I responded to another comment, calories ar

> their body's ability to absorb calories is a limiting factor That depends on what "calories" you're consuming (as I responded to another comment, calories are not just calories). If you're getting calories through animal fat, then indeed absorption is a limiting factor. If you're chugging pure glucose/sucrose dissolved in water, then that limit is significantly higher, and you start hitting the physical limit of how much liquid volume can physically move through your body without it being a torture method. Which actually leads to the primary cause of the obesity epidemic: the prevalence of sugar, and particularly in forms that get directly absorbed into the body.