At a previous job I was delivering milk to schools. I would walk 15-20 miles a day, much of which was pushing a 2 wheel hand truck with 200-300 lbs on it. Didn't take long for me to drop about 20 lbs when I started doing that.
The worst part wasn't the walking, it was the repetitive lifting of all those milk crates. I was delivering 500-700 cases a day, and had to rotate stock. The repetitive lifting was killing my wrists to the point my hands were numb even when I wasn't working. Luckily that went away after I quit.