I suppose that one should consider the TIME of the backpacking trip.

A weekend trip might be just a small fractional pound loss of fat if you are actually producing 4000 Calories of metabolic and work output and consuming just 2000 to 3000 Calories. A two week long trip, on the other hand, would show a significant weight loss.

Some people will tire easily if they aren't consuming the higher caloric load corresponding to the higher caloric output.

There is also the concept of AVERAGE. A randomly selected person isn't necessarily AVERAGE. So, when someone talks about the average caloric requirement, the question to ask is "What makes me think I am AVERAGE (or not)?"