I fast regularly and if you already on a low carb diet, then the transition is much easier on your body. I don't notice a a diminishing of mental capacity, but I do notice that I need more sleep.
There are a lot of things you can do to prepare for a fast. For example, cut back on caffeine, sugar and even salt in the days or weeks ahead of your fast. Also, gorging on food the morning of a fast is not really healthy and is a sure recipe for "Ramadan code."
There was a fantastic article on fasting in Harper's Magazine this past March that covers the history of fasting, "Starving your way to vigor: The benefits of an empty stomach." Sadly, you have to be a subscriber to read it online:
There are a lot of things you can do to prepare for a fast. For example, cut back on caffeine, sugar and even salt in the days or weeks ahead of your fast. Also, gorging on food the morning of a fast is not really healthy and is a sure recipe for "Ramadan code."
There was a fantastic article on fasting in Harper's Magazine this past March that covers the history of fasting, "Starving your way to vigor: The benefits of an empty stomach." Sadly, you have to be a subscriber to read it online:
http://harpers.org/archive/2012/03/0083829
Fasting doesn't have to devastate your mental faculties. I actually find that it helps me focus, and I have started doing it a few times a year.