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I started fasting on Yom Kippur as an adult, about 10 years ago.

A couple times I had to drink a glass of water either after Kol Nidre or before Shacharit, because I felt completely dehydrated (I did go on with the fast after that)

What steps do you recommend to avoid this situation? Foods to avoid during the previous meal? Specific hydration steps?

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3 Answers 3

up vote 10 down vote accepted

Please see "The Segal Guide to Fasting For Yom Kippur (from a Medical Perspective)," written by a physician. The very first point he deals with is the thirst issue you raised.

Hope you have a successful and meaningful fast this year!

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There are many articles online about this. E.g.: jpost.com/Health/Article.aspx?id=240719 –  Ariel K Oct 6 '11 at 16:23
Excellent guide. This is exactly what I was looking for. –  מרדכי בן דניאל Oct 7 '11 at 1:16

From a personal perspective, I have found that the easiest fasts I have had, came when Yom Kippur was on a Monday, and Sunday morning I did a 3-4 hour run (training for a fall marathon).

My theory is that knowing how dumb an idea it is to do a 3-4 hour run, mere hours before a 25 hour fast, I try to compensate by drinking the rest of the day, every 10-20 minutes having a mouthful or two of water at time.

This is actually how I try to optimize hydration during long distance races, but doing it before Yom Kippur seems to have helped.

Based on a comment from Monica Cellio I feel I should add that the reasoning behind hydrating in the described fashion is based on the uptake rate of the typical persons gastrointestinal tract is about 800 mL to 1 litre an hour. So drinking more than that at once means your kidneys will just discard it.

For your stomach to effectively absorb water you want to keep it constantly absorbing, with a small amount of physical pressure. A couple of mouthfuls at a time keeps the stomach somewhat occupied, and the physical presence helps generate a very small amount of pressure that helps the absorption process.

Thus doing this every 10 minutes or so keeps the pressure up, and maximizes the time your body has to absorb the water.

Of course expect to visit the potty a lot as a consequence of this!

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I begin increased hydration (as part of ramping down caffeine) starting right after Rosh Hashana, with the greatest amount of water on the last two days (today and tomorrow). It doesn't reliably solve the headache problem, but it does seem to help with thirst. What you can't do is just chug a half-gallon of water right before the fast (spoken from experience). –  Monica Cellio Oct 6 '11 at 17:26
This is good advice too (accepted Dave's answer as more complete) –  מרדכי בן דניאל Oct 7 '11 at 1:17

I heard a Segula from Baba Sale Zatsal (R. Yaakov Abouah'sera) but I never tried it :

Drink a glass of water in front of the Mezuzah of the room.

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