The Nativity Fast begins today. Here is some background and perspective (when our minds tell us 'this is hard') from the Questions and Answer section at oca.org...
We fast before the Great Feast of the Nativity in order to prepare ourselves for the celebration of Our Lord’s birth. As in the case of Great Lent, the Nativity Fast is one of preparation, during which we focus on the coming of the Savior by fasting, prayer, and almsgiving.
By fasting, we “shift our focus” from ourselves to others, spending less time worrying about what to eat, when to eat, how much to eat, and so on in order to use our time in increased prayer and caring for the poor. We learn through fasting that we can gain control over things which we sometimes allow to control us—and for many people, food is a controlling factor. We live in the only society in which an entire TV network is devoted to food! While fasting from food, however, we are also challenged to fast from sin, from gossip, from jealousy, from anger, and from those other things which, while well within our control, we all too often allow to control us.
Just as we would refrain from eating a lot before going to an expensive restaurant for dinner—if we “ruin our appetite” we will enjoy the restaurant less—so too we fast before the Nativity in order to more fully feast and celebrate on the Nativity itself.
During the Nativity Fast, we are called upon to refrain from meat, dairy, fish, wine, and olive oil. At the same time, we are challenged, within this framework, to fast to the best of our ability, and to do so consistently.
If we must modify the extent to which we fast within this framework, it is of course possible, but in every instance our fasting should be consistent and regular, for Christ does not see fasting as an option, but as a “must.”
In Matthew Christ says, “WHEN you fast, do not be like the hypocrites,” not “IF you fast” or “IF YOU CHOOSE to fast.”
Finally, it seems quite odd that in our society—a society in which people gladly and freely spend huge sums of money for diets, most of which recommend that one refrain from red meats and dairy products—fasting is not more widely embraced. How odd that a Jenny Craig consultant or diet guru or physician will tell us to refrain from eating meat or cheese or butter and we will gladly embrace—and pay large sums of money for—his or her advice, while when the Church offers the same advice [at “no cost”] we tend to balk, as if we were being asked to do the impossible.