Yes sure it is very helpful to fast according to your energy level. Fasting helps the whole energy of the system to focus on digesting the food remains which are stuck in the digestive canal for long and produces toxins which lead to diseases. Fasting helps in eliminating these left outs and cleansing the canal and also, the whole body by creating a vacuum in the digestive tract. Fasting can also be done on daily basis by having just 2 meals/day (Morning & Evening). This gives a good gap between meals and proper time to the system to digest/absorb/eliminate the previous food taken.

what's your problem and symptoms share me some more details