TJ Dillashaw, the UFC bantamweight (61kg) champion, has made weight for his latest fight at flyweight (56kg).

While 5kg doesn't sound like much, it's a lot for a fighter, especially when you're taking on the champion.

And when Dillashaw weighed in at 138 pounds (62kg) last week and made weight earlier today, it's a herculean effort. To make sure he was ready to go when he stepped on the scales, Dillashaw had to shed 13kg in just three months, reports news.com.au.

UFC Fight Night 143 on Sunday (AEDT) will pit two champions against each other with Dillashaw taking on flyweight titleholder Henry Cejudo for the flyweight strap.

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If Dillashaw wins, he will be just the fourth fighter behind Conor McGregor, Daniel Cormier and Amanda Nunes to hold two titles in different weight divisions simultaneously.

What makes this different is that he would be the first to go down a weight division to win a second belt.

It's been tough for Dillashaw to cut the weight, especially with the fight being brought a week forward from its original timing for the UFC's debut on ESPN.

Some UFC fans and pundits think Dillashaw's weight cut has been too extreme.

But Dillashaw said in an Instagram post straight after the weigh-in he was "feeling alive" and "ready to go".

So how did Dillashaw, who needed to drop 13kg in the past three months, safely make it to the weight? Science.

TJ Dillashaw was looking fit as he defended his UFC bantamweight title in August 2018. Photo / AP
TJ Dillashaw was looking fit as he defended his UFC bantamweight title in August 2018. Photo / AP

The bantamweight champ trains in the garage of his strength and conditioning coach Sam Calavitta, a triathlete math professor, aerospace engineer and performance specialist who coaches Dillashaw, Bellator's Aaron Pico and other elite athletes.

Calavitta said he planned out every step in the process even before Dillashaw (16-3) agreed to the fight against Cejudo (13-2).

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"It makes sure to stay within the bounds of safety, so as not to allow the body to go into siege mode — a state of withholding that is basically a never-ending circle you can't get out of," Calavitta told ESPN. "That's where guys end up killing themselves."

For the 32-year-old Dillashaw, it's a bit simpler.

"I am a little f***ing insane," he said. "But it's nothing I couldn't do."

Dillashaw and Calavitta were confident he could do it with a scientific, meticulously measured plan that takes the nearly 33-year-old down to a weight at which the former Cal State Fullerton wrestler hadn't competed since he was a teenager.

"I always knew I could make the weight, but I'm surprised at how good I feel trying to get down there," Dillashaw told the Associated Press.

"It's because of how professional I took it. My diet has been strict. My workout routine has been strict. I'm lean, and everyone thinks I'm lying, but I'm stronger now than I was last camp."

Instead of relying on the mix of crash dieting, sauna sweats and dehydration that has been the time-tested formula for fighters determined to compete at the smallest possible weight, Calavitta and Dillashaw created a three-month regimen of precise eating, working out and constant monitoring of every factor in between.

Every calorie counts in the home-cooked meals eaten by Dillashaw at Calavitta's table, but the plan is much more than a diet.

"We're not really presenting him something that is so much discipline or deprivation as it is lifestyle," Calavitta said. "It's to make your life better now as well as after fighting, so you can spend many, many years with your wife and your kids with a healthy and truthful life without many of the negative effects (of fighting)."

And to the people who are worried about how skinny he looks, Dillashaw said it's not surprising because he wants to get the best out of himself.

"Of course I'm going to be skinny," Dillashaw said. "I'm going down a weight class. If I were to wait and crash all the weight the last night (before the weigh-in), I would look better throughout camp.

"I'd look more normal, (but) then I would have to crash at the end and my performance wouldn't be as good. I'm more worried about the performance."

The UFC world is excited too. Commentator Joe Rogan said Dillashaw's preparation to drop the weight was "insane".

With the UFC flyweight division reportedly on the chopping block, this fight may also reveal plenty about the division's future.

- with AP
This story was originally from news.com.au and republished here with permission