Halakhah su Levitico 16:31

These conclusions may, however, not appear relevant with regard to the prohibition against eating and drinking on Yom Kippur. That prohibition is not couched in a phrase admonishing "thou shalt not eat" but rather in the words "and you shall afflict your souls" (Leviticus 16:31). Indeed, the quantity of food that must be consumed on Yom Kippur in order to incur the biblically-prescribed punishment, viz., food equal in quantity to a dried date, is greater than the olive-size measure which is the quantity of a forbidden food that must be consumed in order to incur punishment because, even though consumption of an olive constitutes "eating," "affliction" is not mitigated by consumption of a quantity of food less than the equivalent of a dried date. It is for this reason that Sha'agat Aryeh, no. 76, declares that partaking of food on Yom Kippur in an unusual manner is biblically forbidden.²Cf., however, Rambam, Hilkhot Yesodei ha-Torah 5:8; R. Jacob Ettlinger, Binyan Ẓion, no. 35; and Teshuvot Ketav Sofer, Oraḥ Ḥayyim, no. 111. According to Sha'agat Aryeh it is negation of the "affliction" experienced in fasting, rather than "eating" per se, which constitutes the essence of the Yom Kippur prohibition. Similarly, Minḥat Hinnukh, no. 313; R. Moses Sofer, Teshuvot Hatam Sofer, Oraḥ Hayyim, no. 127, s.v. tu; and Teshuvot Ketav Sofer, Oraḥ Hayyim, no. 117, s.v. ve-aḥar, maintain that partaking of food on Yom Kippur can entail no biblical violation in the absence of "enjoyment by the intestines" (hana'at mei'av), i.e., unless hunger is at least somewhat appeased by means of digestion.³This view is, however, explicitly rejected by Teshuvot Maharsham, I, no. 124; R. Meir Simchah ha-Kohen of Dvinsk, Or Sameaḥ, Hilkhot Shevitat Asor 2:4; and R. Chaim Ozer Grodzinski, Teshuvot Aḥi‘ezer, III, no. 61. The rationale underlying the opinion of these authorities is that the essence of the Yom Kippur prohibition is the mitigation of "affliction" rather than the act of eating. Arguably, it would then follow that, according to these authorities, any form of nourishment which assuages hunger is forbidden on Yom Kippur.

That is that He commanded us to fast on the tenth day of Tishrei. And that is His, may He be exalted, saying, "afflict your souls" (Leviticus 16:29). And the explanation appears in the Sifra (Sifra, Acharei Mot, Chapter 7:3), "'Afflict' - affliction that destroys a soul. And what is that? [Abstention from] eating and drinking." And the tradition (Yoma 73a) likewise came [to teach] that it is forbidden for bathing, anointing, wearing shoes and sexual relations. And the resting is designated for all of these actions by His saying, "It is a Shabbat of Shabbaton, and you shall afflict your souls" (Leviticus 16:31): It is as if He said that the obligation is the specific resting from work and the specific resting from nourishment for the body and its preservation. And He hence said, "Shabbaton." And the language of the Sifra (Sifra, Acharei Mot, Chapter 8:3) is, "From where [do we know] that [...] bathing [and] anointment [...] are forbidden on Yom Kippur? [Hence] we learn to say, 'It is a Shabbat of Shabbaton.'" That is to say that the resting be from all of these things until he arrives at affliction. (See Parashat Acharei Mot; Mishneh Torah, Rest on a Holiday 1.)

And that is that He commanded us to rest from work and [certain] actions on Yom Kippur. And that is His, may He be exalted, saying, "It is a Shabbat of Shabbaton for you" (Leviticus 16:31). And we have already explained several times that this rest is a positive commandment. (See Parashat Emor; Mishneh Torah, Rest on a Holiday 1.)