For three days of the week eat consume ONLY vegetables and fruits.No dairy, no grains, no meats etc, just fruit and veg. Provided you are fit and have your doctors approval, this is a great way to cleanse your system and kick start healthier eating. It worked for me big time!
You can continue this for as long as you want, provided again you are healthy and have no complications like high/low BP, diabetics etc.
Always consult a doctor or dietitian first though before embarking on any major dietary changes. All the best!