There's also a difference between planning for a week long backpacking trip and a 3 month thru hike. It's ok to run a calorie deficit for a week and tap into fat reserves' while not maintaining a balanced diet (you're not going to get scurvy in a week). Doing the PCT or AT becomes more complex as not only do you need to maintain your calorie intake, but all the other proteins, vitamins and minerals your body needs, on the other hand you'll be resupplying along the way so incorporating fresh foods and real meals along the way is easier