I drink Diet Dr. Pepper when I'm working. It's stored about 25' away from where I sit. So I end up getting up, getting another, getting up to drop one off, and sometimes bending and lifting to restock. I didn't realize how much I was doing for my health until this line of research came up :-).
From a mental perspective however sometimes getting up and walking around the office or the building helps me focus because there are so many windows on my desktop feeding me information.
Here, I think this article actually explains the research better: http://www.nytimes.com/2011/04/17/magazine/mag-17sitting-t.h...