I've walked 45-70km a week (with some fairly sizeable hills) for the last 6 months - I'm fitter than I was 6 months ago, but no lighter.
THAT could have had something to do with the beers you enjoy at the end of the hikes .....
But seriously, have you analysed body composition? I'd bet you've changed fat into muscle (muscle weighs more than fat) over that time ..... what about waistline? A little bird told me you lost 2 inches - that also indicates body composition changes.....
Losing 4 pounds is very easy, losing 4 pounds of fat is another matter: 1 pound of fat equals 14 000 Calories. On average, women's daily caloric expenditure is around 2000 Calories while men spend roughly 7-800 more.
Obviously this number can vary greatly depending on metabolism and activity. Contrary to popular belief, there isn't a huge difference between running and walking in terms of Calorie expenditure if the people cover the same distance. The rough formula is 1Cal/kg/km so a 90kg person running 10km would roughly expend 900 Calories regardless of whether running or walking. The walker might simply take twice as long. However regular running as been shown to increase metabolism and the more muscle one has, the higher the metabolism so there's still an advantage to running and exercising at higher intensities.
As you can see, in order to lose 4 pounds of fat, someone would have to complete 10km every day while cutting around 1000 Cal every day. Not what I would call easy...
Try GM diet General Motors: Weight Loss Diet Program
Its doable and it works for me, 4kgs lighter.