How to increase the rate of absorption and assimilation of food?
The rate of absorption is controlled by two essential physical factors:


Contact surface between intestinal content and intestinal mucosa.
Time of contact.


There are many other factors including intestinal peristalsis, gastric, pancreatic and bile secretions that stimulate/help absorption.

So increasing or accelerating intestinal passage of food won't do any good (see diarrhea). Water will not be absorbed into the blood flow thus leading to dehydration and hypovolemia. Also the alimentary principles, vitamins, essential aminoacids won't be absorbed.

On the other hand, slowing down the passage has negative effects. It allows bacterial saprophytic flora to multiply so much that those microorganisms become pathogenic by producing toxins. And increased contact time equals increased absorption both of toxins and food principles.