A discussion on fasting is not complete until a few words are mentioned on the wrong ways of fasting. Fasting is NOT atonement for sin. Children have developing bodies and care should be taken when involving youngsters. There is a dangerous life-threatening condition called anorexia nervosa, and these afflicted individuals should not be armed with additional excuses for avoiding treatment and recovery.
There are a number of passages found in the letters of St Paul that are critical of asceticism in general, and seem to suggest that it is a false virtue. In fact, this is the main reason Paul makes the final cut. If we were left with just the 4 canonical Gospels, we would not know what to make of them, and Christianity would really be a free-for-all – “Jesus fasted for 40 days; hey, let me see if I can go 80”.
Adam and Eve ate until their stomachs were full, and they did not eat a single morsel more. They had sex until they were satisfied, and then they just went on with the rest of their day. Unlike our bodies, their bodies were balanced, and their appetites controlled and kept within healthy limits. The primary result of original sin is a separation from God. And consequently, people find themselves in a continual state of need, and trying to compensate for this loss by overeating or seeking out sexual thrills, and all the other sins. Fasting is first about regaining some control over the body, and thus allowing us a chance to develop spiritually.
Hope this helps