This is exactly what Tim Ferris, author of The 4-Hour Workweek: Escape 9-5, Live Anywhere And Join The New Rich (great book btw), did when he competed in the Sanshou (an eclectic form of kung fu) national championship in 1999.
When arriving on the site he weighed 187 lbs and wanted to lose weight so he could compete in the 165-lb weight class. He lost 22 lbs (about 10kg) in 20 hours by severely dehydrating himself (80% of you is water).
To achieve this, he combined:
- Temperature treatments (very hot baths) to lose water through the skin.
- Using diuretics (dandelion root and caffeine) to lose water through urination
After the weigh-in, he gained 28 lbs (about 12kg) by rapid hydration so he would be in optimal condition to compete.
Needless to say this is not healthy and in fact very dangerous (some athletes die doing this). These techniques don’t make you lose fat, only water and are only useful for competition sports. Don’t try this at home!
Read more on Tim Ferris’ blog here.
Here’s a video of a Sanshou competition: