As you train to restrain yourself from eating and drinking, you will gradually restrain your tongue from bad talk and from any talk that is not constructive. You also restrain your mind from vain and wrong thoughts.
You restrain your heart from all sinful feelings, all desires and impure emotions. And so you will progress from the fasting of the mouth to the fasting of the tongue, the fasting of the thoughts, and the fasting of the heart.