OpenOffice .odt file is huge. How do I shrink it?

An Apache OpenOffice 4 text document (.odt) that I edit pretty often has gotten huge: 189MB, even though it's just text (112 pages). It really shouldn't be anywhere near that bit, even with the few embedded images that are in it.

This LibreOffice forum thread describes the issue but doesn't offer a solution.

How do I see what's taking up all the space? Troubleshoot it? Fix it?

With Apache OpenOffice 4, a simple Save-As (with the same .odt extension) reduced it from 188MB to 660KB, and a pretty careful side-by-side review of the two documents tells me everything is in the new one.