Dehydration
About 65% of the human body is made of water under normal conditions. This makes it tempting for athletes to temporarily lose weight through dehydration prior to weigh-ins. This weight can then be rapidly regained immediately afterwards.
A good rule of thumb for most athletes is to lose no more than 5% of their total body weight through dehydration. Athletes at an elite level often lose more than this. It should not be attempted without a knowledgeable coach and medical supervision.
Immediately before weigh-ins, athletes can put on warm clothes and engage in aerobic exercise to make themselves sweat. Garbage bags can be worn against the skin to eliminate cooling through sweat evaporation.
Some athletes choose to sit in a sauna so that they can sweat without wasting energy. Another technique is to chew gum to induce salivation, then to spit out the saliva instead of swallowing it.
Athletes should remember to urinate and defecate as this is an easy way to reduce weight. Some athletes may choose to take diuretics and laxatives to aid in this. Some diuretics are banned by the WADA in events such as the Olympics as they mask Steroid detection in post drug tests, some may also have harmful effects on the body.
Losing weight through dehydration is not recommended, as it may lead to decreased performance, and, more importantly, serious injury.
Read more about this topic: Weight Cutting