In reply to Dan Bailey - UKHillwalking.com:
According to the Mountaincraft and Leadership book by Eric Langmuir (excellent book, by the way), once you have DER (Daily Energy Requirement), add 10% for each of the following:
* for every 500m ascent;
* in winter or adverse conditions, either overhead or underfoot;
* if a full rucksack is carried.
DER (obviously, these are estimates which depend on many other factories):
15-18 y.o. - 2755 for males and 2110 for females
19-50 y.o. - 2550 for males and 1940 for females
Also, it is said that hillwalking requires 600 kcal per hour.
It seems quite impossible as I tend to do over 12 hours walks with little rests and can consume less than 2000kcal a day (100-150g of protein). I've done 42km long walk with 3192m ascent in 16 hours 50 minutes (including rest time) in rather good weather. I had 12-13kg rucksack and I'm sure I didn't consume 4200 kcal. But again, I've got some body fat and my body is quite adapted to be able to cut intake for a week or two. It was 9th day of my trek, hence I was used to the pace, rucksack, etc..