Comment by PaulDavisThe1st

6hrs a day @ 3 mph = 18 miles per day, 100 calories per mile without packs = 1800 calories per day on top of basal metabolic needs. Given your user name, I'd guess that you're male, and given that you're hiking the AT and have already started, I'd also guess that you're younger rather than older, so I'd peg your basal metabolism at around 2200-2400 calories. Add in the packs and the hills, and it should be clear why you're losing weight.