While these fruits are healthy and do provide a lot of good vitamins, they also contain too much sugar. It’s ok to have a couple of pieces of these fruits as a part of a fruit salad. However, Mangos, grapes, oranges, watermelon, and kiwi have a lot of sugar per serving. When you eat these fruits frequently, it could slow your weight loss down by causing your body to release high amounts of insulin. Remember, your body is either in a fat burning mode or a fat storing mode. It won’t be in both at the same time. Therefore, if your body is releasing high amounts of insulin to counteract the large quantities of sugar in these fruits, it is in fat storing mode.