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Old 08-04-2014
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Default Optimizing water retention during Ramadan intermittent fast?


First, sorry if I'm writing in the wrong sub-forum, I just have no clue what all those' steps' are about. I'm a French student in nutrition so I'm a bit lost here, but I don't know of any other forum where I could ask my question.

I am writing a dissertation on the physiological implications of the Ramadan fast, and I have read in several sources that pre-loading the body with salt and water just before the fast (at dawn) could help slow down dehydration during the day.

I don't get how this is possible... Don't we have a very fine system to regulate salt and water, and flush out any excess?
I thought excess salt/water would increase the GFR, and activate the atrial natriuretic peptide and suppress aldosteron and vasopressin, thus effectively ridding plasma of all the 'pre-loaded' salt and water... What are your thoughts on this?
Thanks in advance.
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Old 08-05-2014
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Wow. This looks like a really difficult question for step 1 concerning the physio/renal section. Sorry cant help you with that. And this question would probably be better off in the step 1 section.

Also try looking for another forum. A physiology one maybe? I don't know
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Old 08-05-2014
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That's a very interesting topic. I haven't read about it before but these are my thoughts and my personal experience from fasting in Radmadan.

Fasting is almost 16 hours (varies according to the region), before fasting, people drink a lot of water hoping that this will suppress the thirst sensation which is partially true. Excess water increases blood volume and decreases its osmolarity. This will decrease ADH and release ANP, Aldosteron levels are affected as well, GFR will definitely increase. Within the first 2 hours of fasting, all the excess water we drink is urinated and the blood is euvolemic again and back to the normal osmolarity. So, true fasting time is actually less 2 hours.

From that point, the body will get into starvation mode. ADH will start to increase again, GFR will decrease to decrease water loss but it will not be Zero of course to maintain blood volume and osmolarity ACCORDING to the person's physical activity and how much sweat the person is losing. If the person does nothing, he won't be losing too much fluid and he will have minimal thirst sensation.

If the person is losing too much sweat and the reduction in GFR can't keep up to compensate for the loss, by the end of the day, blood volume will be low, therefore ADH will be very low, hypothalmus will induce thirst sensation. All of this is very basic. What is really interesting is that with time, the brain is adapted to thirst and fasting gets easier as if the normal osmolarity/volume default point as shifted (this is not scientifically proven though as far as I know).

Before the fasting the person is not preloading with salt and water. He is preloading with water. If the person eats a heavy meal before fasting, blood will be hyperosmolar, GFR will decrease, ADH will decrease as well and he will be thiristy the whole day untill the body gets rid of that excess salt, this is not possible though without losing water as well, and because the person is fasting and abstains from water intake, his osmolarity will be higher the whole day.
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