I lost 16+ lbs. (need to look at my notes to see what the exact tally was). I had a belly visible through my running shirt in pics from the day I walked into Roncesvalles. By Sahagun, it was pretty much gone. By Santiago de Compestela, my belt was critical for keeping my pants up -- despite the nice tan and feeling fit, I looked like I needed a good meal. That is not to say that I did not eat well on the Camino.
A tangent: A few days after starting in SJPdP, I started craving protein. It was an odd experience, especially given that I ate excellent, well-rounded meals during those first several days. Perhaps a week into the Camino, I stayed at an albergue that had braised cow tongue as one of the pilgrim meal options. I had reservations about ordering it -- that's not something seen very often on the American dinner table. Fortunately, the protein craving won out. Braised cow tongue ranks as one of the most memorable and satisfying meals I ate while on the Camino.