# This obligation applies even if one is not hungry, <ref> Shulchan Aruch 291:1. Kaf Hachayim 291:3 quotes the Chida saying that one should really make that extra effort because one would normally would eat a meal friday night and shabbat morning anyway so the afternoon meal is the only one that is clearly for the honor of shabbat, and proves that the first two were as well. </ref> but if one can not eat at all then one is not obligated to pain oneself, as this would violate oneg shabbos. Nonetheless, a wise person will see ahead and leave room for Suedat Shelishit. <ref> S"A 291:1 </ref>
==What to Eat?==
# One must eat bread for Seudat Shelishit, however, if one is very full and is unable, then one should eat Mezonot. If that is also impossible one should have food which usually accompany bread such as meat or fish or at least fruit (cooked fruit is preferable). If one doesn't have fruit then one may use a [[Revi'it]] of wine. <ref> The above is from Yalkut Yosef ([[Shabbat]] vol 1 pg 409).
* Tosafot Yoma 79b "minai" says that one must eat bread based on the connection between seuda shlishit and the manna. Rambam Hilchot [[Shabbat]] 30:9, Tur 291, SA 291:4-5 all accept this opinion. Rabbeinu Tam quoted in Tosafot Brachot 49b "ee ba'ay achil" allows eating minei targima to fulfill the obligation of seudat shlishit based on Rabbi Eliezer's statement on Succa 27a who says that you can fulfill the obligation for a meal on succot with minei targima. Rabbeinu Yona on the Rif Brachot 36b "Birkat" agrees. The Rosh Brachot 2:13 says that minei targima are foods made from one of the five species of grain based on a Tosefta that says that the beracha on minei targima is borei minei mezonot. Tosafot to Succa 27a "minei targima" say that foods which usually accompany bread such as meat or fish are included in this as well. Rashi "minei targima" there, as well as Rabbeinu Yona Brachot 36b "birkat," and the Ran [[Shabbat]] 44a "v'ika" include even fruit in this category.
* Shulchan Aruch 291:5 quotes all these opinions and concludes that one should eat bread.
* Kitzur S"A 77:16 writes that One must eat bread for Seudat Shelishit, however, if one is very full and is unable, then one should eat Mezonot. If that is also impossible one should have food which usually accompany bread such as meat or fish. If that too is impossible one should have at least fruit cooked fruit.
* Aruch Hashulchan 291:12 says that it is not proper to rely on any of these opinions unless one is sick.
* Magen Avraham 444:2 when discussing what to do on erev pesach that falls out on shabbat gives several options and also quotes the Shla saying that one may fulfill seudat shlishit with divrei torah. The Rokeach 55 allows one to skip seudat shlishit to go here a shiur in the afternoon. Pri Megadim (E"A 290) disagrees and says one shouldn't miss seudat shlishit even to hear a shiur. Aruch Hashulchan 290:3 and Kaf Hachayim 290:14 agree with the Pri Megadim.</ref>