Originally Answered: long distance running weight loss?
That depends on how much you do long distance running, on the intensity, and the same goes for the sprints in comparison.
If you sprint regularly, doing 8 - 12 sprints per session, sprinting to your absolute max speed, then you should be at a lower body fat percentage than if you regularly did long distance runs at a casual or intense pace. Sprinting makes you lose fat, not muscle, therefore it is superior for fat loss.
Long distance running is superior for overall weight loss, that is both fat and muscle, runners outside of the elite levels are usually 'skinny fat' they are very light, very thin but they aren't lean or defined, often being a little bit flabby and soft. Long distance runners are noticeable fatter.
So it depends what you want:
If you want pure weight loss, then run longer distances more regularly, this may damage your knees btw.
If you want pure fat loss, then do sprinting as it will speed up your metabolism, and make your muscles larger, more pronounced and give you the lean, ripped look.
Also, yes your body probably is used to running long distances. It's good to switch it up to confuse your body and to put different types and levels of strain on your muscles and nervous system.
Try cycling and swimming various distance as various intensities, try weight lifting, try bodyweight strength training (push ups, pull ups, crunches) ,try walking (trust me it really works) and try HIIT (High intensity Interval Training) plyometric circuits too (burpees, alternate leg squat thrusts, skipping etc.)
Don't stick to any set routine, interchange all the different types of exercises I listed.
If you eat healthy and count calories then maybe you should look at the sources of your calories, many carbs are considered healthy but are bad for weight gain. Carbohydrates are more readily stored as fat in the body than fat itself! Cut out even the healthy carbs such as fruit juices, porridge/oatmeal, wholegrain bread, rice, pasta, spaghetti and noodles.
Don't forget to get plenty of water, vitamins, minerals, protein, fibre and fat :D .... but not too many minerals, that can be damaging ^.^