mental acuity detriment?

Hey y'all.
I'm a second time faster on day 2 and I was wondering what everyone's experience was in relation to mental effects of the fast. I am a university student with high academic demands, and I really hope that this fast doesn't hurt my GPA (joke). I was at the checkout like at Whole foods and the guy said he had a hard time "doing his job" because his mental acuity was affected. What might that mean for me?
Oh yeah and what are the PB shakes about? Does that involve peanut butter, cus I love peanut butter!

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