Weight reduction is related to energy balance.
If energy intake > energy expenditure, then you gain weight. It is as simple as that.
Run fast or run a long distance can both increase your energy expenditure, so basically both can help you reducing weight.
However, your body use fat as the main energy source during mild to moderate exercise. Therefore, I recommend you running slower but longer distance.
Also it is difficult to keep running very fast for whole 30 minutes.
For diet, quantity and quality of food are both important. For example, if you eat many many energy-dense food e.g. coke, cake, cookies, ice-cream, then although you eat 6,7成飽到, you may still gain weight. Therefore you should avoid eating energy-dense food.
Remember a can of coke gives you around 300kcal and you need to run around 20 mins to burn this 300kcal.
My opinion is that:
Don't be too obsess about the exact figures of e.g. speed, heart rate, time.
Keep doing at least 30mins moderate exercise (i.e. you breath faster than normal and have some difficulty in talking with friends during exercise) regularly (e.g. 4-5 days per week) and reduce eating energy-dense food (e.g. soft-drinks, cakes, chips) can reduce your weight steadily.