FYI - I have done a Water Fast for 4 days while working and juice fast for 14 days while working. My guess is that it will depend a lot on your current state of health whether you will feel find working all day while fasting. I am not on my feet most of the day (desk job). I find that day 2-3 I am wiped out and I go home and sit until until bedtime which will be early. That's about it. Good luck. :)