I personally think the answer to your question is "not necessarily" . . . if your body is used to that kind of lifestyle, and you feel strong in your body, you should be good to go. I have had more energy on this fast in my experience, but, do take my advise with a grain of salt, as I am far from an "expert" on this subject. Plus, everyone's body is different and reacts to certain activity differently at different times. . Maybe take a light run and see how you feel?