MadSci Network: General Biology

Re: Does gravity assist digestion ?

Date: Wed Apr 25 14:45:57 2001
Posted By: Stacey Kohler, Secondary School Teacher, General Science, Kissimmee Middle School
Area of science: General Biology
ID: 984912780.Gb

I have been able to find no evidence that gravity aids digestion.  It 
certainly can't hurt; after all, we evolved in an environment with 
gravity.  It seems natural that gravity would help pull the food down the 
esophagus, hold it down in the stomach, and help it move into the 
intestines.  Gravity would also seem to help in the process of eliminating 
the final outcome of digestion. But I can think of no place where food 
merely falls, or is allowed to rest.  

All of these processes occur because of the movements of the various 
muscle groups associated with the digestive system.  Muscles in the 
esophagus push food down (patients with paralysis of the esophagus are 
unable to swallow.)  Food doesn't rest calmly in the stomach; instead it 
is squeezed and mixed with various juices and enzymes.  The squeezing 
process also moves food out of the stomach into the small intestines, 
where muscles continue to move the food along the loops and twists and 
turns.  Finally, both defecation and urination can happen without the 
assistance of gravity, as anyone who has had to change the diaper of a 
baby lying on its side can tell you.

NASA's website,, has little information on this subject.  The 
best I could find was a question from an Australian schoolkid to Andrew 
Thomas, an American astronaut that spent some time on Mir.  He reported no 
effects to his digestion.

This was a great question that provoked some interesting thoughts!  I hope 
the debate continues in a friendly manner.  Thanks for using MadSci!

S. Kohler, your Mad Scientist du jour

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