your energy level and weightloss, depends on if your juice fasting ,water fasting, or like me I am protien drink fasting, if your Water Fasting you will most likely have very little energy, and Water Fasting gives you the fastest weightloss, juice fasting you will most likely lose 1-2 pounds a day, and with any fast you will feel tired ,weakness the first 3 days atleast then off and on through the fast you will have times of energy and times of tiredness and weakness , and many people have headaches and some body aches off and on.I choose the protien drink to fast on because it gives me more energy then the juice, and also I still lose weight, I also take multi vitamins.Love Lisa