There is a Mitzvah of eating on Erev Yom Kippur. The Gemara says that this Mitzvah is so important, that who ever eats on Erev Yom HaKippurim, he gets credit as if he fasted on both the ninth of Tishre and the tenth of Tishre. So here’s a case where your eating gets chalked up as a fast.

The question is why? What’s the concept in having to eat on Erev Yom Kippur? The Rosh says a Mashal (analogous story), to a father that knows his son is going to have to fast so the day before he feeds him and he gives him choice foods and things like that, because he doesn’t want his son to get hurt from the upcoming fast. So too G-d, although we have to fast on Yom Kippur, he doesn’t want anyone to get hurt on Yom Kippurim, so therefore he commands us to eat, so we will be physically prepared and able to endure the fast the next day.

The Shibule Haleket however, has a totally reversed explanation. He says on the contrary. He says it’s much harder for one to fast the next day when he eats a lot the day before a fast. It’s almost as if his stomach expands, and his stomach gets used to eating a lot, and then he stops cold turkey, and the next day he doesn’t eat anything. And that’s what the Torah wants. The Torah wants you to feel the pain. The only question on that opinion is, if such is the logic so why on Tisha BeAv, we don’t have such a thing to eat extra the day before? Before Tisha BeAv, you are supposed to have minimal food at the last meal. Unless we can make a difference between Tisha BeAv which is really more for Avelut (mourning), so it might be different than Yom HaKippurim.

In any event the Sifat Emet, also brings an explanation down, which should be pointed out. The Sifat Emet says a novel explanation. The whole Mitzvah of Aseret Yime Teshuva is to ask forgiveness from our friends. And he says that a person who is not satiated may not be in a mood to go to his friends to ask for forgiveness. When a person doesn’t eat, he is nervous, and edgy. So therefore they say to eat well on Erev Yom Kippur, so you feel good and are comfortable, so you can be in a better mood, so that you can go to your friend and ask for forgiveness or give him appeasement.

The Minhag was brought down to eat the amount of two days. So each one has to figure out what he normally eats in a day, and try to eat double the amount on Erev Yom Kippur. It’s even more important than learning. There are few things that we put ahead of learning Torah. But the Halacha says that one should even minimize his learning, to go sit down and have a meal. The meal comes first. The proof of this is from Gemara Berachot, page 8. The Gemara says, [listen to the audio clip for the exact quote,] a story where a Rabbi was learning a lot on Erev Kippur, and his students came to him and said what are you doing? They told him, ‘you have to eat today, why are you reading all day long, and now you are not going have the time to eat?’ He could have answered back that nothing is more important than learning, but he didn’t. So you see that eating even precedes learning Torah.

Are ladies obligated in this Mitzvah? Halacha says that they are. Because the reasons apply to them also. They also are fasting on Yom Kippur. So if you take the reason of the Rosh or the Shivule Haleket or Sifat Emet, since the reasons apply, so Chacham Ovadia says that ladies are obligated to eat also.

There is a custom, the Ben Ish Chai writes, to eat fish on Erev Kippur. And he says the custom is specifically in the breakfast. Where did this custom of eating fish on Erev Kippur come from? The Tur brings down a story from the Midrash. It says one day the king told his servant to go to the market place and buy a piece fish for him. So the servant went to the market place and there was one piece of fish left. So the servant offered one Dinar (money) to the vendor for the fish, which was a lot of money. But there was a Jew there, and he said that he would pay 2 Dinars. And they ended up bidding, and the Jew ended up paying 5 Dinars, which was a very expensive price. So the servant came back to the king and told the king that there was no more fish, and that a Jew bought the last piece for a lot of money. So the king called the Jew to the palace, and he said to him, what is going on here, why did you pay such a high price? So the Jew explained to him that today is the day before Yom Kippur, and we have a Mitzvah to eat. So therefore, since there was an occurrence where you saw a guy that went all out, and spent all sorts of money to buy food, and specifically it was a piece fish, so that’s as if it brings a good memory and in front of G-d, when we have fish on Erev Kippur.

We do not want people to have emissions from their body on Yom Kippur, whereby one can become unholy. So, there are certain foods that you should not eat after breakfast. These types of foods include fish, hot milk, eggs, dates, and more. One should be careful not to eat them past breakfast. Additionally, we should be careful and avoid fatty meats at the Seuda Mafseket (last meal), because that too can cause one to have emissions on Yom Kippur.