I have sometimes had trouble with both eating and drinking enough on tour in the hot weather on hard climbing days. I lost 22 pounds on my last tour (4 weeks one of which was a stop over in Yosemite). While I am happy to have the weight off, a tour isn't the best time to do it IMO. I would have felt much better if I could have eaten enough to keep my weight steady or just lost a smaller amount. The thing is... I couldn't even force more food down on that tour.
The lack of appetite is not an always thing for me. I ate like a pig on much of the Trans America and I ate moderately well on my Santa Fe Trail tour..