On Shabbat, three meals (seudot) must be eaten. This mitzvah applies to both men and women, without distinction. For the first two meals, it is necessary according to all opinions to eat bread to fulfill the mitzvah (the measure of “kabezá,” which is 54 grams). Regarding the third meal (seudá shelishit), although halachically it should also be eaten with bread, there are opinions that consider it can be fulfilled with another mezonot food made from wheat or barley, or other grains from the five grains (tacc).
Some opinions suggest it can be fulfilled by eating meat or fish, or any other food served at the meal (except fruits), and some consider it can be fulfilled by eating fruits. Therefore, although halachically it is best to also have the third meal with bread (preferably 54 grams or, if very full, 29 grams), if it is not possible to eat bread (due to being very full or another valid reason), it can be replaced with a mezonot food, or meat, fish, etc. Or alternatively, with fruits (in that order of priority). It should be noted that the obligation to eat the third meal should not be taken lightly, as it is on the same level as the other meals, and according to Kabbalah, this meal has a very special level.
