Lines 20-25 of the original poem whose analysis the book is built around run as follows
Si tu dures
Now I, even reading Hofstadter's "boring literal" translation,
If thou stayest
Thou wilt acquire,
And will lose
Thy plump form
somehow made the mistake of reading "prendras/acquire" and "perdraslose" as both having "l'embonpoint/plump form" as their object. I could try excusing this by the fact that my ignorance of French let me think that Couleur fade was somehow a complete clause, meaning something like "[your] colour will fade" but it looks like it's just a noun phrase "pale color" which is the complement of Tu prendras that follows it. But really the literal translation should tell me that's wrong, since "Pale shade" is no kind of sentence.
Anyway, I was pleased in a way to find out that Robert French, a professional translator and by all accounts quite a smart guy, had made the same mistake. His verse translation contained the lines
If you stay
Ill this way,
Pale and drawn,
You'll put on
But then cede
Pounds you need.
And Hofstadter gleefully points out the error, and how its fix automatically fixes another error in French's translation that French didn't think was an error at all: not matching the line-count of the original. Oh, Hofstadter.
I also found an esperanto translation on the web. Dolĉega!