Is it one main meal? Two other meals which together do not exceed the main meal? It gets complicated. Besides that, when you set up those kind of rules, there are always ways around it - like income tax.
The best description seems to be simple: A major reduction in the amount of food I eat on given days.
Fasting has a way of clearing the air so that the real issues surface. That's what happened to Jesus. After he fasted for 40 days, he faced squarely the chief issue of his public life: Whether he would follow the Father's way, or follow a path that, to him, may have appeared more realistic.
Fasting for a blood test doesn't make things right. It clears the way to see what needs to be set right. It's the same with fasting. When you clear food our of your life, you clear the way for a "spiritual" blood test. You see things you've never noticed before.
There's a relationship between the food you eat and your body. When you fast, changes occur in your body and brain, e.g. the body's metabolism slows down, the brain's metabolic functions may produce special clarity, euphoria, etc.
The Gospel speaks of the transfiguration and the vision shared with the disciples. Fasting actually makes a person see things differently - to look beyond the ordinary.
How do you fast today?
How do you start fasting in small steps?
- Little Black Book, Diocese of Saginaw