Fasting can be useful for certain rituals or treating certain ailments, but otherwise fasting is unnecessary and can even be harmful, distracting, debilitating, etc.
We recommend that you eat a healthy diet to keep your body strong. Good physical health is the basis of good psychological and spiritual health. When you starve the body, everything else weakens, too.
The only useful and important way to fast is to starve the ego of its food, which is entirely psychological.
"Do not worry; cultivate the habit of being happy." - Samael Aun Weor