I did lose weight on my longer tours. I had a problem eating enough which I consider a very bad thing when on tour.
Losing a moderate amount of weight over a long tour is OK, but it should not be a goal of the tour IMO. It is hard enough to stay fueled when on tour without intentionally running a deficit.
On long tours I tend to struggle to take in enough calories for the first month or so and then do better from there on. I lost more weight than I would have liked on the first 30 days of the Trans America and gained maybe half of it back in the remaining 43 or so days. The portion of the Sierra Cascades that I did last year was about 30 days and again I lost too much weight, but was doing better about when we finished. I wish I could just manage to eat more right from the beginning.