My record is 12 days. I start intensely craving things for their electrolyte content late in the week, and like you, I'll eat a sofa cushion on day 3, but after, it's smooth sailing and the brain sort of gives up being manic about food.

I'll crave things like pickle juice. Clearly the body wants its salts. It's amazing how good it is as signaling the things it needs, when it needs them.

My wife will make some really appalling beverage for me, containing pickle juice, apple cider vinegar, lite salt, and I think lemon juice. It terrifies me to think about. On a fast, though? I'll literally drink it by the quart and want more.