A little more than 24 hours before Georges St. Pierre stepped in the cage to defend his welterweight championship against Jake Shields at UFC 129, he weighed 170 pounds. By the time he throws his first punch in Toronto, the MMA standout will weigh 192 pounds. In one day, St. Pierre packs on the equivalent of two-year-old child. But how?

A common practice in both mixed martial arts and amateur wrestling, "cutting weight" has been a topic of intrigue and wonder in the sports community for some time. Often criticized as unhealthy and downright dangerous do the lengths these athletes go to in order to “make weight,” the process has become more fine-tuned — almost a cult science for a certain group of experts.

GSP's trainer, Firas Zabai, opened up about the method to The Toronto Star.

"He's on a protein and vegetable diet. Right now his exercise is significantly cut, but he's going to shed water," he said. "It's only temporary weight loss. It's not real weight loss. You're not dropping fat."

The majority of St. Pierre's weight is knocked off with this diet, but the final pounds are sweat out in the sauna. Sitting and sometimes exercising in intense heat allows the fighter to drop as much as 10 pounds in pure water weight. It can be a gamble. For some competitors, the drying out process leaves them sluggish and lethargic in the cage. Not the kind of state you want to be in when going up against a trained killer.

Even Zahabi himself is suspicious of the sauna, but he insists it works because GSP’s body is so used to it.

“I don't recommend this to anybody, even professional athletes,” the trainer said. “This is somebody who's very seasoned.”

Will St. Pierre's drastic weight change have an impact on his big title defense? Check out UFC 129 to find out.

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