There are five prohibitions on Yom Kippur. All learned from the biblical verse: (Vaikra 23:27): 'On the 10th of Tishri, you should deprive yourselves..."
The five prohibitions are:
(1) Eating and drinking, (2) washing our body (3) anointing our body (4) having marital relations and (5) wearing leather shoes.
Everyone has to fast on Yom Kippur, except:
1. Minors: a boy or a girl younger than 9 years old should not fast, even for a few hours. When they reach 9, they might fast for a couple of hours, but only if they are in good health. In the following years the parents should encourage them to fast for a little longer so they will slowly get used to do a complete day of fasting. When the son or the daughter reach 11 years old, they should try to fast the whole day, if they are in good health. A healthy girl from the age of 12 and a healthy boy from the age of 13 are obligated to fast, as everyone else.
2. Mothers: After childbirth, during the first 3 days, a mother should not fast. The same rule applies for the first 72 hours following a miscarriage. After 72 hours from the time of childbirth until the 7th day after birth, if the mother says that she needs to eat, she should eat. After the 7th day she has to fast, unless otherwise indicated by a physician. A woman in labor cannot fast. (Pregnant women, see here).
3. Sickness: A person who is sick or weak because of his age, or a treatment and is getting medication, should get the advice of a knowledgable physician to see if he can fast and/or stop taking his medication for a day. After talking to a Doctor a Rabbi could help the patient to plan how to eat his food (see below). In a case of a chronic illness, such as diabetes, and especially in a case where there is a risk (Safek) of endangering someone's life, one should break the fast even if one is not able to consult with a physician.
According to Jewish Law, if a Chole -a sick person- asserts that he or she needs to eat, he or she should be fed, even without asking a Doctor.
If you were instructed by your doctor to eat on Yom Kippur, and you don't need to eat a large amount of food or liquids at once, you should proceed as follows:
1. Eat a portion of food that weights less than 1 Oz. (1 ounce = 30 grams). After you finished the first portion you should wait ten minutes and eat a second portion, less than 1 Oz. . You could do this, until you recover.
2. For drinking, you should drink up to a little more than 1 Oz. Then, wait 5 minutes and drink 1 Oz. again, and so forth.
If possible, once you feel better, you should continue the fast.
To measure "1 ounce" it is advisable to use the plastic 1 Oz. liquor shot cups (Kiddush little plastic cups).
The Meaning of Kol Nidrei
The extraordinary history and lesson of this moving prayer.
by Rabbi Jonathan Sacks