Are they sure i will loss weight if i breast feed.

Maybe: Depending upon how much the baby eats, you can lose 500-1000 calories per day beyond what you normally burn. So, as long as you don't eat more you should be able to lose some weight.

Balanced nutrition: If you eat a well balanced diet based on your pre-pregnant weight ( calorie wise) & simply breast feed, you can lose a pound every week or two.Make sure you are taking prenatal vitamins & plenty of fluids. The loss will be slow but natural. The books that say to up your calorie intake to bf are assuring that you won't lose weight.