Mixed Martial Arts (MMA) has seen a rapid rise in popularity. Figures like Conor McGregor have helped elevate the sport to a whole new level.
We may even be about to see MMA meet boxing in a 'billion-dollar fight' if McGregor and Mayweather get their act together.
It's a brutal sport inside the octagon, but new footage now appears to show that it's just as tough outside, with fighters going to extreme lengths just to shed pounds before a fight.
The process - known as 'weight cutting' - is potentially more deadly than the fight itself.
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Credit: BBC/The Weight Cut: Extreme Weight Loss
Using severe dehydration tactics, such as 90-degree saunas and boiling baths, the sportsmen and women are able to lose weight to compete in their chosen category.
Dean Garnett is the star of a new BBC Three documentary,The Weight Cut: Extreme Weight Loss.
Credit: BBC/The Weight Cut: Extreme Weight Loss
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In the show, he drops from 10st 8lbs (69kg) to 9st 7lbs (61.8kg) in just 19 hours.
Part of the Extraordinary Bodies series on the online channel, Dean is followed as he goes 'nil by mouth' in an attempt to lose 7kg before his fight just 24 hours later.
It's a dangerous process which has already claimed the lives of two MMA fighters.
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Leonardo Souza, aged 33, cut 33lbs in a week but collapsed and died in a sauna while Yang Jian Bing died of a heart attack.
Credit: BBC/The Weight Cut: Extreme Weight Loss
Credit: BBC/The Weight Cut: Extreme Weight Loss
Credit: BBC/The Weight Cut: Extreme Weight Loss
Dean, so obsessed with losing pounds, weighs his urine after going to the toilet and chews endless bags of ice before spitting out the water to help cut calories.
He says he's aware of the mental and physical torture he is putting himself through, but blames the lack of weight categories as a reason for it.
Dean said: "I don't like over-sensationalising it, but obviously people know there is a problem.
"If there were more weight classes this weight cut thing wouldn't be worth documenting, I just hope it doesn't take more people dying.
"People ask why you do it, but potentially you can earn millions, you want to be the best."
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Dean's mentor, also seen in the programme, Ben Crighton, is a PhD researcher at Liverpool St John Moores University.
Ben said: "The reason it is so dangerous is because of the amount of weight that MMA competitors are cutting through dehydration."
At the end of this programme, Dean's fight ends in a draw and he begins to eat normally again.
Dean said: "All of a sudden your fight is over and you tell yourself you've got this month-long window of opportunity to stuff your face.
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"And then you stuff your face and you start the next fight camp dead big - it's a vicious cycle."
MMA remains a sport with no regulatory body, yet it delivers some real knockout blows. While some see it as a brutal sport, others see it as a chance to see fighters display a wide-ranging set of combat skills.
Featured Image Credit: Credit: BBC/The Weight Cut: Extreme Weight LossTopics: MMA