is it ok to cleanse the body by fasting sometimes?

There is no scientific proof that it will help the body detox. Fasting to cleanse the body seems to have no biological explanation because the body is quite capable of doing it on its own. The liver is the body's natural detoxification centre. Toxins are eliminated by the lungs, colon, kidneys, lymph glands, and skin.
It's debatable if fasting can help the body clear itself of waste buildup. Fasting, on the other hand, has long been utilised for religious and spiritual purification.