If you watch Tv and pay attention to commercials you will notice that every few advertisements there an add for a weight loss pills, or a diet. The ironic part is that they always followed by a fast food commercial.
Most diets advertised do not provide adequate nutrition, therefore they can leave the dieter in a poor state of health, with damaged metabolism. Especially when they are the extremes, it surprises me how far people will go to loose weight. Even if you do end up loosing weight on an extreme diet, your body will develop a lower capacity for burning calories, this is why everyone who does loose weight gains it back.