There are a few days a year in which certain religions fast.

I was wondering if there's an evidence based approach for absorbing a lot of water before to help keep oneself hydrated. I was reading this question about the speed at which we should drink whose answer was positioned towards rehydrating. Other articles recomends avoiding chocolate, tea, coffee and salt. I would have thought though that adding salt to your water while loading up for a fast day would help you absorb more of it because it will counteract some of the water (meaning it will say in you and not be excreted).

How should one consume salt and water in the days leading up to a fast?

  • What kind of fasting is meant here? Totally avoiding both food and water for the entire day for more than one day? Or fasting just for some hours within a day?
    – Jan
    Commented Sep 29, 2017 at 11:39
  • Totally avoiding food and water for a continuous 24 hour period.
    – wizlog
    Commented Sep 29, 2017 at 15:30

1 Answer 1


OK, so this seems to be a 24 hour fast.

Salt (sodium) and glycerol, after drinking water, prolong the time in which the water is excreted from the body, but they both work only for few hours.

The idea of hyperhydration to delay dehydration sounds interesting for marathon runners (in order to avoid the need to drink during the race), but according to American College of Sports Medicine, only few hours after hyperhydration, you will likely lose the excessive water.

Attempting to hyperhydrate with fluids that expand of the extra- and intracellular spaces (e.g., water and glycerol solutions) will greatly increase the risk of having to void during competition...

Glycerol can also have side effects, such as diarrhea.

I am not aware of any nutrient, supplement or food that would keep the water in your body in any meaningful manner in a 24-hour fasting scenario.

The effect of fasting is that you feel the lack of benefit of food. The resulting hunger can then remind you of things, other than food, that are important for you. Resisting from food alone (while drinking water) can already have this effect. Hyperhydration before fasting would cancel the effect of resisting from water, so what's the point of this, anyway.

Saying that, I am not promoting or suggesting anyone to resist from drinking water for any amount of time, because it could be potentially health- or even life-threatening.

If one has to survive for 24 hours without water and food, the means to avoid dehydration can be:

  • Keep yourself well hydrated before fasting.
  • Avoid alcohol and caffeine before fasting because they can promote the excretion of water through the urine.
  • Avoid/limit anything what promotes sweating, such as exercise, exposure to sun and excessive clothing.
  • +1, good answer. Saying that, I’m not promoting ... life-threatening. You might want to use markdown to make this part stand out, that’s really important!
    – Narusan
    Commented Sep 29, 2017 at 17:07
  • can you please source alcohol and caffeine promoting excretion of water?
    – wizlog
    Commented Oct 1, 2017 at 13:29
  • 1
    Optimally, a highlight should be also added to "so what's the point of this, anyway". Commented Oct 1, 2017 at 15:43
  • 1
    @wizlog, I added a link in my post that points to a detailed explanation (with studies mentioned) that caffeine and alcohol act as mild diuretics.
    – Jan
    Commented Oct 2, 2017 at 6:53

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