Here is my latest article for Catholic Online on why we should fast.
Suddenly I understood why the monastic tradition in every religion insists on asceticism. To concentrate on the spiritual, the monks and nuns strictly discipline their physical lives. They narrow their lives down by staying in one place. They take vows of poverty so they are unconcerned about the accumulation of wealth. They take vows of obedience so they can be unworried about personal choices. They discipline their bodies through fasting so their minds can open up the realities of the spiritual realm.
This is the main reason why we are expected to fast: to discipline our physical appetites in order to concentrate on the spiritual realm. Rather than being satiated and dull as the result of too much food and drink, fasting makes our senses sharper and we become more aware of the spiritual realm.
Read the whole article here.