+1 on Low carb isn't no carb. I had fantastic results on low carbs. I tried no carb once and it really will fk with your brain. Don't try no carbs!!!
Interesting. For how long?
I have seen people fast (i.e. no calories, but water and minerals etc) for two weeks, without too much messed up brains.
From what I've heard reported[1] about periods of extreme caloric restriction is that it takes the body around 4 days or so to start dealing with the lack of carbohydrates. Until that point the person feels tired, grumpy, headachy, out of sorts, hungry.
[1]act 2: http://www.thisamericanlife.org/radio-archives/episode/259/t...