some online calculator told me that running with medium tempo for an hour with my approximate weight should equal to 1000kcal. since fat has 4-5kcal of energy per gram, that should translate to 200g of fat / hour. which should mean that running 5x per week for an hour should make me lose 1kg of pure fat. so to lose 10kg means 2.5 months of running one hour per day during the week and resting through the weekends. i think that is doable, as long the body holds up and the will lasts.