Yes, but don't just lose weight,  exchange fat for muscle.  Specifically work 4 muscle groups.  Abdominals and paraspinals (back muscles) for supporting the weight of your pack, quads for going down hill and gluts for going up hill.  If you have a gym membership, they will have lots of machines to target these individual muscle groups.  If you don't, you can do wall squats progressing to single leg wall squats progressing to single leg squats progressing to single leg squats with your pack on.  For your gluts you can do bridges progressing to single leg bridges progressing to single leg bridges with a 1 minute hold.  For your core muscles, elbow planks progressing to elbow planks with your pack on should do.  

I also suggest using 2 treking poles.  They will take about 25% of the weight off your legs.  I also add extra padding to my shoulder straps and hip belt using wool seat belt shoulder harness covers.  Just use a hot melt gun to hold them in place.  It's usually not the weight that bothers us so much as it is the pressure points where that weight makes contact with our bodies.  Namely our hips and shoulders.

So all my reccomedations have been to either exchange weight or add weight, but in all these cases the added weight will produce more than it will cost.