How to reduce iOS app data size?

First off, let me just say that I LOVE NewsBlur. The syncing between desktop and app is my favorite feature!

However, I have noticed that on my iPhone, the app’s documents and data is slowly growing in size, taking up a little over a gigabyte of space. I only have 9 feeds!

I have tried erasing offline stories in the preferences, but this doesn’t seem to help reduce the data. Is this just the way it is?