Is digestion effected by low gravity?

Well, given that some people have spent more than 100 days in space -- it would seem that digestion is not affected by zero gravity.

These people spent 185vdays in space :

http://en.wikipedia.org/wiki/Soyuz_35

When we eat, food does not just "fall down into our stomach. The esophagus propels the food down :

"During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach."

That's from this article :

http://en.wikipedia.org/wiki/Esophagus

And once in the stomach, food can not pass back up, because all movement in the digestive tract is one way, controlled by peristalsis (muscular contractions of the walls of the entestines and esophagus.

The movement of food through your body is by a process called peristalsis. It is a series of muscular contractions which pushes the food through the gut. It doesn't appear to be affected by microgravity.

So long as your vagal nerve still functions, your digestion is unaffected by micro-gravity.