I am another that has a headache the day after fasting. It’s like the whole head being slightly compressed, which I thought was just dehydration, so drank more. No real effect.
So I read somewhere about ORT (Oral Rehydration Treatment) helping and decided to try. It worked. No more headaches. You can buy the cheap powder sachets at any chemist or online.
The ORT powder has salt and sugar as the active ingredients and the sugar is about 15cals so you have to figure that into the daily total, but having read more about the way the body processes salt into the stomach etc it’s a good possibility that the significant food reduction on fast days is the cause because modern foods have so much salt in them. I’ll leave it up to the Doctors to confirm this.
I have experimented with no ORT on fast days and days with 3 sachets: 12am, 6pm, 9pm and it works every time. Take ORT and no headache next day.
Hopes this helps those (and it seems a lot) who have the same problem.
10:42 am
8 Mar 14