A celebrity has to look good always,or almost always,so they have to take care of their look.
Here are few tips of losing weight.
Some celebrities use drugs to loose weight( see Anne Nicole Smith),some use crash diets(this is available for short periods),some dance till the sunrise in order to burn calories( a good way to get rid of some calories),some do sport( this is one of the healtiest way to loose weight),some eat whatever they like and then they throw up(this is awful,don't try this ever),some use colonic irigation( in order to clean the unwanted bacterias and loos weight).
Either way you choose in order to loose weight,i think the best way is always to be careful what you eat and do sport as much as possible.
In the top of the most skinniest celebrity are:
Mary Kate Olsen,
Lara Flynn Boyle,
Victoria Beckham and many more