Fasting cleans out your system

This is misleading. When we fast, there may be less bowel action because there is less dietary fibre and starch resistant to small intestinal digestion to enter the large bowel. It is here that fermentation, increased microbial bulk and water retention in faeces occurs. These processes are important for the healthy function of the large bowel and fasting for long periods denies this function.

A day or so of minimal food intake, while maintaining adequate fluid intake, may allow the body to readjust excessive appetite or readjust its energy balance (see WE NEED NOT WORRY ABOUT NUTRITION IF WE HAVE A BALANCED DIET) after excessive kilojoule intake. But this is not latter of cleaning the system.