How do I eat and drink on Yom Kippur with Shiurim?
If one is required to eat on Yom Kippur due to medical reasons, a Rov should be consulted in advance to receive specific dispensation from fasting. However, in case of a medical emergency where one’s life is in danger, or even if there is a question whether the condition is a medical emergency or not, the patient should be given food or medicine immediately.
They should not attempt to fast against the rabbi’s orders. The same Torah which commands us to fast on Yom Kippur tells us that guarding our health is far more important than fasting on this holy day. Just as a healthy person fulfills a Mitzvah by fasting; an ill person does a Mitzvah by eating.
A person who is required to eat or drink due to illness, but afterwards feels strong enough to fast, must resume fasting.
One who is weak and can only fast if he remains in bed all day, should not attempt to go to Shul or Daven, rather he should fast and remain in bed. Attending Shul and/or Davening are of secondary importance in comparison to the biblical obligation to fast.
Although the eating or drinking on Yom Kippur is forbidden even for tiny amounts, however, when fasting is dangerous one should, whenever possible, eat or drink less than a Shiur (the prescribed amount delineated below) at a time. While it is Biblically forbidden to eat or drink even less than this amount, but such an offense is not punishable by Torah law. One is only “culpable” when eating at least 2/3 of the Talmudic measurement called “K’beitzah”, or drinking at least a mouthful of liquid, within a short period of time.
The Shiur for drinking is half of one mouthful (measured before the fast by filling the mouth and cheeks with liquid, emptying it into a measuring cup, and dividing it into half).
If eating is necessary, one may eat up to 30cc (cubic centimeters) at a time. (About the size that fits into a small matchbox).
Ideally, these quantities should be consumed at intervals of at least nine minutes; however, if that is not possible one can be lenient with intervals as short seven, six, or even four minutes. If circumstances require eating and / or drinking even more often, one may be lenient.
Eating and drinking can both be done simultaneously within the same time slot.
When one is required to eat, no Kiddush is recited on Yom Kippur. (This applies even when Yom Kippur falls on Shabbos). Before eating bread one must wash hands as is done throughout the year. There is no need to have two complete Challahs, as is required on all other festivals. There is a difference of opinion whether the holiday Ya’aleh V’yavo is reciting during benching.
See the following for information on pregnant/nursing women on Yom Kippur:
I just gave birth/I am nursing. Do I have to fast on Yom Kippur?