This article is from the Diet FAQ, by Claudia McCreary cookignnewsletter@chef.net with numerous contributions by others.
Although it's tempting (and motivating) to lose a lot of weight quickly,
this really hurts you in the long run, since you'll be losing muscle mass
long with the fat. A rough rule of thumb is that you should lose no more
than 2 pounds per week, with 1/2 to 1 pound being better. A more precise
rule is that you should lose no more than 1 percent of your current body
weight per week, so if you weigh 250 lb. (113 kg.), you could safely lose
2.5 lb. (1.13 kg.) per week. Again, this is a maximum weekly rate; to be
safer still, aim for .5 percent of your current weight. Study after study
indicates that the slower you lose weight, the more likely you are to
actually lose fat, rather than muscle tissue, and that the slower you lose
weight, the more likely you are to keep that weight off permanently.
 
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