Mango is rich in fiber, a good source of Vitamin A, an excellent source of minerals (potassium) and is rich in antioxidants. 100 grams of mango has nearly 70kcal, most of them from carbs!
Go ahead and include mangoes in your diet..you only need to make sure that you are not exceeding your total calorie intake!
PS: Eating mangoes DOES NOT make you gain weight. Excess calories does!