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Imagine becoming heavyweight champion of the world - by knocking out a fighter who's never been knocked out - and still having to worry about people calling you fat.

Andy Ruiz Jr's astonishing win against Anthony Joshua looks like a victory for anyone who's been mocked for carrying a bit too much timber.

To the untrained eye, the Mexican certainly looked hopelessly out of shape - with slo-mo replays merely highlighting his wobbly torso.

But Newsbeat's been finding out how all that fat might actually help you fight.

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"In a sport like heavyweight boxing there are certainly scenarios where carrying extra body fat can be beneficial," says sports nutritionist Dr Mayur Ranchordas.

He's worked with anyone from pro-boxers Gavin and Jamie McDonnell to diver Tom Daley - and says it's all about recognising the delicate balance between muscle, fat and fitness.

Image copyright Getty Images Image caption The famously large Eric "Buterbean" Esch in 2001 after one of his many, many knock-outs

"When we train athletes in the lab the first thing we do is measure their body composition - how much muscle mass they are carrying and how much fat mass they have around it.

"If you want to become a good cyclist, extra body fat is of no use whatsoever because that additional weight doesn't translate into performance. In boxing it can.

"If you're an extra 20 kilograms heavier - even if that weight is coming from fat - the opponent is going to feel your punch a lot more," he explains.

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So extra weight can enhance power. But, of course, there is a trade off: fitness and agility.

"If you are carrying extra body fat then your heart rate is going to be higher and you're going to have to use more energy to move around."

Before a fight boxers go into training camps where, usually, the aim is to lose fat mass and increase muscle mass.

To tone up, basically.

But Dr Ranchordas says - as long as an athlete is fit enough to handle the extra weight - the fat can be helpful.

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"If your ability to produce speed is great, your punching power is phenomenal and your fitness levels are very, very good - getting you to lose an extra 15 kilos of fat is probably not going to help."

And that brings us back to Ruiz.

"Ruiz is carrying a lot of body fat - but don't get me wrong he's carrying a lot of muscle mass at the same time. He's not just a fat blob.

"So how does he differ from an overweight guy down the street? That guy might weigh the same - but underneath the fat he's carrying nowhere near as much muscle."

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