Unlike animals, which satisfy their hunger in a mechanical, instinctive way, man has refined his approach to food so as to make it part of human civilization. It is natural for men to enjoy tasty food. If you are walking along a country road and you see a fruit tree, heavy with ripe, tasty fruit, you are not allowed to pick one and eat it without the permission of the owner. Yet, if you do, you are only satisfying a natural desire which is closely related to your existence. As you know, without food we cannot live more than a few days.
All human beings agree that only goods obtained in a legitimate manner are permissible to eat.
You cannot just take what does not belong to you. You have to buy it or be given it as a present. Otherwise, you commit a sin if you take it away. The same applies to the satisfaction of natural tendencies of establishing a relationship which must be legitimate and the only legitimate relationship in this connection is that of marriage. The fact that the attraction is natural does not mean that we can seek its satisfaction in an unruly or undisciplined manner.