Earlier quoted context omitted.
> I’ve never believed this — only because my weight is so consistent and my eating is not. That's only one side of the equation. It is a basically proven fact (and largely implied by physics) that `calorie intake - expenditure = net weight change`. That is pretty much beyond dispute. It is also true that some things affect expenditure, and it seems likely that most people have a "set point" that your body attempts to…
Could also be that the incredibly complex digestive system isn't just a food mulcher but is capable of moderating caloric intake based on any number of parameters.
No, our digestive tracts are extremely good at extracting any and all usable calories from our food.
100% of the time, when someone makes this claim, they are mis-estimating either their intake or expenditure, or not tracking for a long enough time period to escape the error bars inherent in daily hydration variance.