Also, the amount of calories that are not for some reason not picked up through the intestine, and instead consumed by bacteria in the large intestine. And prob

Also, the amount of calories that are not for some reason not picked up through the intestine, and instead consumed by bacteria in the large intestine. And probably much more. I think this is a field of knowledge where the holes, certainly so for a layperson, are huge. Fructose malabsorption is a concrete example of this, although I'm sure there are many others.