Fasting for Yom Kippur: A Medical Perspective

Michael M. Segal MD PhD

Each year on Yom Kippur, Jews wish one another a khatima tova (a good seal in the Book of Life) and a tolerable fast.  The route to a khatima tova is beyond the scope of this article; the route to a tolerable fast is described here.

Don’t get thirsty

Most people think the difficulty of fasting is feeling “hungry.” Actually, avoiding thirst is much more important for how you feel.  Not only do you avoid the discomfort of thirst, but your mouth isn’t dry, so you swallow frequently, and your stomach does not feel as empty.

One important way to remain well hydrated is to avoid drinks or foods that cause your body to get rid of water, such as alcohol and caffeine-like compounds in coffee, tea, and chocolate.  Another important factor is to avoid consuming much salt (sodium chloride) on the day that the fast begins.  Salt causes a person to feel thirsty despite having a “normal” amount of water, because extra water is needed for the extra salt.  For this reason, you should avoid processed foods containing lots of salt such as pickles, cheese, tomato sauce, commercial salad dressing, sliced meats, most breads and salted fish (it is Yom Kippur, not Yom Kipper).  Since kosher meat has a high salt content it may be best to choose a main course for the pre-fast meal such as fresh fish, canned no-salt tuna fish or de-salted meat such as boiled chicken.

By avoiding these types of foods and drinks in the day before a fast, you can avoid either losing water or needing extra water.  Other actions that cause the body to lose water, such as perspiring in warm clothing, should also be avoided during the fast.

Don’t start the pre-fast meal on a full stomach

The pre-fast meal often begins in the late afternoon, so a large lunch could prevent you from eating enough in the pre-fast meal.  It is best to have a small lunch, or no lunch at all.  A large breakfast early in the day based on cereals, breads and fruits can provide the energy you need during the day, yet these high-fiber foods will be far downstream by the time of the pre-fast meal and will not keep you from eating enough food at the pre-fast meal.  A large breakfast is also helpful because it stretches the stomach.  After eating breakfast, it is best to consume primarily liquids during the day.  This will not fill you up, since liquids are absorbed quickly, and this will ensure that you have absorbed enough fluids during the day to start the pre-fast meal being well hydrated.  Be sure to avoid beverages with alcohol or caffeine.  You should also drink at least two glasses of fluids with the pre-fast meal because many foods need extra water to be digested properly.

Eat foods that are digested slowly

Include some foods high in oils and fats in the pre-fast meal since such foods delay emptying of the stomach and slow down digestion of your meal.  However, beware of fatty meats or salted potato chips that could load you up with too much salt.  Salads and other high fiber foods that are so important in one’s normal diet should be de-emphasized for the pre-fast meal since they travel quickly through the digestive system.  Fruit, despite its high fiber content, is worthwhile since it carries a lot of water in a “time-release” form.  Avocados or salt-free potato chips, despite containing a lot of potassium, are good choices because the body largely handles potassium by taking it up into cells.

Don’t get a headache

Withdrawing from caffeine-like compounds produces a headache in people who are accustomed to drinking several cups of coffee a day.  If you consume that much caffeine-like compounds in coffee, tea, or chocolate you should prepare yourself by reducing or eliminating these from your diet in the days before Yom Kippur.  Don’t try to get through the fast by drinking coffee right before Kol Nidre, since this will cause you to lose a lot of water.

Make the meal tasty enough so people will eat

The pre-fast meal doesn’t have be bland.  Spices such as lemon or herbs are fine for fasting, but salt, soy sauce and monosodium glutamate should be reduced as much as possible.

Don’t do a complete fast if you have certain medical problems

People with certain medical conditions such as diabetes should consult doctors or rabbis before fasting.  Certain medications need to be taken even during Yom Kippur, and it is important to swallow them with enough water or food to avoid pills getting stuck on the way to the stomach and damaging the esophagus.  Fasting by women who are pregnant or are breast feeding can also be dangerous.  If a young person who has not fasted much before has unusual difficulty fasting you should discuss this with a doctor since this happens in some serious metabolic conditions in which fasting can be very dangerous.

Don’t eat improperly after Neila

Even people who have prepared well for fasting will be hungry after Neila.  Be sure not to eat food too quickly at the post-fast meal.  Begin the break-fast meal with a big glass of fluid, but don’t drink too much at once since that can damage the brain.  Expect to drink as much fluid in the post-fast evening as you drink in a regular day; however, do this over several hours.  Drinking fluid both counteracts the dehydration and occupies space in the stomach, discouraging you from eating too rapidly.

Be careful about eating high salt foods, since you will still be somewhat dehydrated and if you eat a lot of salt you will need to drink a lot of fluids to avoid waking up extremely thirsty in the early morning hours.

These preparations for the fast of Yom Kippur will be different from your normal routine, but they can serve as a concrete reminder of the approaching Day of Atonement.

Copyright 1989 - 2020 Michael M. Segal, MD, PhD. 

See also:

For an article on fasting for Yom Kippur written from the perspective of a runner and a rabbi by the late Rabbi Richard Israel click here

Other Yom Kippur fasting articles: