Fasting is pretty extreme. I don't have experience with diets, this is the first time I try to lose weight but I did some research before I decided what to do. There are sites on internet that will tell you depending on your height, weight, censored and age what is your basal energy need. This is the energy your body needs to survive without doing exercise, this is the energy you need for your heart to beat, to breath, to keep your body temperature constant and so on. Mine is about 1450 cal/day. On top of that you need energy for your daily living activities and exercise you do. To keep you healthy you body needs at least 1200 cal/day intake. If you burn 2000 cal/day with your basal needs and the exercise you do and eat only 1200 cal/day, you will have a deficit of 800 cal/day that will be taken from your body reserves
. 1kg of fat is about 8000 cal, so if your deficit is 800cal/day in 10 days you will lose 1 kg. From what I managed to find out the best results are with a good diet, 1200-1500 cal/day combined with exercise. This is what I do, and I try to find ways to burn more calories instead of cutting the food.