Wow--18 days is amazing!
Just to be clear, how do you and your DW define fasting?
I told someone last week that I was fasting and mentioned that I was drinking coffee, and she gave me a surprised look. She said something like, "Oh, you're drinking coffee? Well, then maybe I could fast for that long as well." I wasn't sure what she meant, exactly, but she's a bit peculiar anyway...
When I fast, I allow myself to drink water, tea, and coffee--very rarely do I drink anything other than those things anyway. And I eat nothing.
You (and your DW) have definitely inspired me to try for longer fasts--so thanks!