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Benefits & Side Effects

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A lot of people find that their first one or two fasts are marred by headaches or even migraine.

I have looked into the possible reasons for this in answer to a query from a member and thought it would be worthwhile putting them here in the FAQ.

There are two reasons for getting headaches during the first couple of fasts:

One is not drinking enough. Food contains a lot of water so by not eating we are not taking in as much water. One symptom of dehydration is headache. You need to drink far more than you think in order to compensate for the lack of water you are having in food.

The second reason is low blood sugar. Although the body has a great system for swapping between glucose as a fuel to glycogen stores and eventually to fat stores, when we are overweight the body is reluctant to swap to fat burning (this is called metabolic inflexibility). This is at least partly due to high insulin levels which act to prevent the fat stores being mobilised. Because the body is slow to swap to fat burning, it fails to compensate for the lack of glucose in the blood (by producing ketone bodies through fat burning), the resulting low blood sugar combined with no ketone bodies leaves the brain short of fuel and triggers a headache/migraine. I think this may also be a contributory factor to those headaches that we sometimes wake up with...we all fast while we sleep (unless we sleepwalk to the fridge and have a midnight snack) and often we start fat burning overnight, perhaps when we wake with a headache we didn't manage to make the switch to fat burning.

After the first fast, the body will change more easily to fat burning, and over the next few fasts the headaches/migraines will disappear. Of course this applies to the other low blood sugar symptoms as well.

Ketone bodies, which are produced during fat burning and which the brain uses instead of glucose when glucose is in short supply, have been shown to be very beneficial to the brain and enhance nerve growth as well as damping down over-excited nerves as occurs in epilepsy and in migraine. In fact, before the dawn of anti-epileptic medicine, a ketogenic diet (i.e., low carb/high fat) was used to help control epilepsy.

So to avoid migraines you need either to keep consuming carbohydrates and risk attendant obesity problems or to try to enter a state of ketosis. Fasting will do this, but you do have to weather the migraines/headaches. A possible way to help the transition into fat burning would be to eat a low carb diet at least on the day before a fast and during the fast and to do some exercise while fasting. This encourages the switch. ... n-fasting/
Loss of sodium etc due to the "natriuresis of fasting" (a good search term to try) is I believe a major factor, and drinking more will probably make that worse unless the water has some salt added.

Rehydration salts and IV saline are used to treat dehydration, not buckets of water, so it rings true. ... n-phinney/ ... fects.html
Great info thanks! I think cutting down on carbs the day before a fast is a great idea.
I went to bed with an awful headache after yesterday's fast. This morning at six I could barely lift my head off the pillow I was in such pain. I have been fasting since September. I'm fasting for other reasons than weight loss and just would like to maintain my weight or lose, at the most six pounds. I haven't lost much since end September but have lost inches. When i started fasting I got headaches so began to drink more water. Yesterday I had a glass of water on the go at all times. I went swimming - 50 lengths and took a bottle of water with me as the air in the pool is hot. It was when I came back - round 3 the headache started to pull me down, lifting slightly when I ate my meal round 7pm - salty WW soup; hummus, half a pitta, lots of raw veg, salt, an orange and an apple, black tea, more water. Maybe this was just a one off and had nothing to do with the fast. I got up at 7, had a boiled egg and a slice of toast and have drunk 3 mugs of tea this morning so far. But I still feel the headache nudging me if I try to do too much and cancelled my exercise class. Any thoughts anyone? Interested to read that too much water can be a bad thing and about the ketones.
I have an absolutely raging headache which started yesterday about 8pm (my first fast day). Although it could be from any of the above reasons I'm betting on it being caffine withdrawal - I usually drink 5 or 6 coffees a day, but I can't drink it black, so only had one yesterday about 6pm as I didn't want to use up all my cals on milk. I'm planning on cutting down the coffee on inbetween days & hope this helps, try and wean myself off.

If anyone has any ideas in the meantime I'd be happy to hear them!
I get a shocking headache on fast days from caffine I drink coffee with milk and sugar I can't afford the calories for a normal coffee, but I do have half a cup of black coffee (which I hate) in the afternoon just to stop the headaches - and it works!
Thanks for the tip Libby - I will maybe have to force myself to have some.
You could try a can of diet cola, I think Pepsi max has the most caffeine in it. In the longer term it would be best to wean off the caffeine but Pepsi max is a good stop gap for fast days.
This rings true for me. I had a migraine on my first fast, but have had no problems since (6 weeks in).

Incidentally, I probably have more caffeine on fast days (3-4 black coffees) and usually forget to drink much water too.
Hey uw_photographer are you the same person who is currently sitting across the room on their iPad (don't you love the digital age, no need to talk to your spouse)
Chicken broth works wonders. Very low cal and high in sodium.
by uw_photographer » Wed Feb 13, 2013 7:40 pm
This rings true for me. I had a migraine on my first fast, but have had no problems since (6 weeks in).

Incidentally, I probably have more caffeine on fast days (3-4 black coffees) and usually forget to drink much water too.

Nikipins wrote: Hey uw_photographer are you the same person who is currently sitting across the room on their iPad (don't you love the digital age, no need to talk to your spouse)

:lol: :lol: :lol:
Thought I had better check with hubby that he is uw_photographer (he is) or might just have propositioned an unsuspecting guy :oops:
It was a fairly mild proposition. If you wanted to tell him something a bit stronger, just use a PM ;)
It has taken me years to get any sort of control over my migraines. I am getting severe migraine the day after fasting so will have to stop fasting for now. All this info above is interesting and I understand it as I am a nurse, but severe pain speaks lounder and I cannot go through the pain.
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