@ George,
Running is a really good cardio activity which helps to loose fat from overall body. Our body have a tendency to get adapted to certain activities if we do it in regular basis so its really important to keep on doing any variations in our workout like running so as the body weight dosent reach a plateau. This variation can be in a frequency, pace, type of exercise pattern. So if we talk about running, running for 5 kms is a great workout and so we can put some variation in it like jogging and running alternately for 15-15 min, Running and jogging alternate days, etc. This type of variation will keep on challenging your body system to help achieve your goal.