Ekadashi is a Hindu fast before the new and full moons, so every fortnight. It means "eleven" in Sanscrit, and occurs eleven days after the full land eleven days after the new moons. I've observed it every once in a while for a couple of decades, and i think it is a very good idea. I've come to think the human digestive system, like everything else, is keyed in to moon cycles, and it is very good to reset the system, particularly before the new moon. Eating light or not at all befor the full moon helps one to channel that energy. Here is a link.

www.ashram.org/ashram_info/vratinfo.html