Assume the smoothies have the same nutrient profile as a regular diet. Like if you drank runny mashed potatoes and protein powder to simulate a normal food intake.
If you do poop because of the nutrients, is there a healthy diet at which waste products are no longer left in the intestine to turn into poop?
Drag has no intention of doing this, drag is just curious about the science.
It’s the optimal for our digestive system, of course in some cases like in the hospital or nursing home people have trouble with getting the correct diet they then get laxatives to help.
That’s not actually an answer. “It’s needed because it’s optimal”, that doesn’t explain any science. Drag wants to know the science.