Not that cleansing hasn't been around for ages but I hate fad diets. Once in a conference room working through lunch every presumably straight man was on a different diet, and everything everyone was eating was alarmingly dissected and discussed. (Needless to say, my egg whites and relatively enormous portions were a hit.) This one was on Atkins, that one South Beach, another vegan. Each looked worse than the next, each lost weight, and each gained more than they lost back. A sensible healthy diet from which you can occasionally stray and treat yourself is the only way to go.
Fasting for health has been around for at least as long as early physical culturist Bernarr Macfadden (http://www.milk-diet.com/classics/macfadden/chapter3/chapter3.html
), and oldtime movie star Gloria Swanson was big on fasts and enemas (another craze rediscovered a few years ago and redubbed "colonics"). An occasional fast (juices for two days a few times a year, maybe) could prove beneficial, but in terms of weight control nothing is a better substitute than eating clean and exercising portion control if need be the rest of the time.