Several years ago, for the first time ever, I observed completely the fasting laws for all of the Jewish holidays that required them. There are six for me. If I was a male and firstborn, there would be seven. That makes 5 minor and 2 major fasts.
The minor fasts, listed below, last from dawn to nightfall and one is permitted to eat breakfast if one arises before dawn for the purpose of doing so (but you must finish eating before first light). There is a great deal of leniency in the minor fasts for people who have medical conditions or other difficulties fasting.
(1) The Fast of Gedaliah, Tishri 3, commemorates the killing of the Jewish governor of Judah, a critical event in the downfall of the first commonwealth.Depending on the fast day and what it means, fasting can mean different things. It can be conducive to atonement, the mode of expressing remorse with a small twist of guilt. Joel 12:18 says "Yet even now," says the lord, "return to me with all your heart, with fasting, with weeping, and with mourning..." Another reason for fasting is to express and mourn loss. This is done as a community, and is a very powerful expression. Fasting is also an opportunity to turn inward, to focus on the spiritual. By denying the body fulfillment we are able to better appreciate how dependant we are on G-d/G-d's creation.
(2) The Fast of Tevet, Tevet 10, is the beginning of the siege of Jerusalem. It has also been proclaimed a memorial day for the six million Jews who died in the Holocaust.
(3) The Fast of Esther, Adar 13, commemorates the three days that Esther fasted before approaching King Ahasuerus on behalf of the Jewish people. The fast is connected with Purim. If Adar 13 falls on a Friday or Saturday, it is moved to the preceding Thursday, because it cannot be moved forward a day (it would fall on Purim).
(4) The Fast of the Firstborn, Nissan 14, is a fast observed only by firstborn males, commemorating the fact that they were saved from the plague of the firstborn in Egypt. It is observed on the day preceding Passover.
(5) The Fast of Tammuz, Tammuz 17, is the date when the walls of Jerusalem were breached, another major event leading up to the destruction of the First Temple.
The two major fasts are (6) Yom Kippur and (7) Tisha B'Av. The fasting restrictions on Tisha B'Av are similar to those on Yom Kippur: to refrain from eating and drinking (even water) for 25 hours.
Fasting, like every other spiritual practice, is layered and one can get simple adherence to Jewish law out of it or one can transcend to even deeper levels of the practice. I have always found the practice of fasting meaningful and have for quite some time observed them in their entirety. (Exception: I did not fast while pregnant, but I did observe the minor fasts while breastfeeding and the major ones in part by drinking water when needed to keep my milk supply.)
It is a disappointment to me that fasting seems so permanently out of my realm now that I have diabetes. As a start, since my diagnosis is new, I am not fasting this year at all, not even in a modified way. I am still moving toward stabilizing and learning where that eat-exercise-blood-sugar balance is. In a way though, I am mourning a little bit that I am not fasting. That I am not engaged in the same struggle as my community. That I can symbolically and intellectually know these things but without the fast, it is just not the same. This year, I feel off and even a little bit disconnected.