Your body is a magnificent machine. It takes in raw materials - oxygen from the air, and water, carbs and proteins in your food - and uses them to work out, shoot baskets and play symphonies. Then it eliminates the unneeded toxic byproducts - carbon dioxide, uric acid, lactic acid, and other natural byproducts of life.
But living in civilization, our bodies encounter many more toxins every day: in the air we breathe, in the water we drink, in the food we eat. Pesticides, heavy metals, residues of molds and fungi... our body is in a constant struggle to clear these things out.
Over the years we fall more and more behind, and both kinds of toxins build up faster than we can eliminate them, gumming up our works, slowing metabolism, causing aging and disease.
Thus, we cleanse. The cleansing process helps our bodies flush these toxins out, leaving us feeling healthier, stronger, and literally rejuvenated - "restored youth".