But very few fighters fall into the vegetarian class, and even fewer heavyweights go that route. But that's what Frank Mir did for a year before deciding it wasn't working for him. Now on a Paleolithic, or "caveman," diet, Mir said he's bigger than he's been in several fights – but more importantly, he's leaner.
"I got on the scale on Monday at 272 – muscle weighs a lot," said Mir, who fights fellow Las Vegan and sometimes training partner Nelson on Saturday at UFC 130. "Going off the vegan diet, I think, helped. There were some good approaches to it that I actually tried to do. ... The dieting thing, I think you have to approach as intelligently as you can. First I started as a vegetarian. And for a whole year, I gave it a shot. And it kept my weight down. But honestly, my body fat wasn't as low – I got a little bit softer. I was getting injured a lot more. I felt a lack of 'umph.' But I was very determined to try and be a healthier person."
After researching the Paleo diet, which focuses on hunter-gatherer foods like lean meats and fish, fruits and vegetables, nuts and seeds, and cuts out the processed foods common in the Western diet, Mir decided it might be more in line with his nutritional needs as a fighter.
And then his wife, whom Mir joked at Wednesday's press conference was the real boss, chimed in.
"My wife looked at (the Paleo diet) and said, 'This is the Mediterranean Diet,' Mir said prior to the press conference. "I'm like, 'Yeah, pretty much.' She said, 'This is how we've been eating for like the last 10 years.' Sometimes you've got to come full circle to appreciate where you are now."
After Mir stopped with the vegan principle, he said the weight gain came quickly.
"I was four pounds shy of 300 pounds – I completely shot up," the former UFC heavyweight champ told MMA Fighting. "But my strength felt incredible, and my wind actually didn't feel that bad. The only thing I probably lost a little was footwork – ask a 300-pound guy to dance left and right ... so I worked in the pocket a little for those couple months."
But the weight gain hurt him in training, and it forced him to tighten up his core once again.
"I didn't realize that now that I've thinned out my waistline again, my guard has returned to be pretty manacing again," Mir said. "With the half-guard and guard, if you have a belly it's hard to pull your knees up. I have very flexible legs, so I'm trying to put hooks in and work the omoplata and go off on the side, and all of a sudden I've got this belly that my thigh keeps hitting against. It hurt my style.
"But being a professional you realize if something's in the way of you being a better fighter, it has to go – be it friend, family member, eating habits, sleeping regimen, if it doesn't work to make me a better fighter then it has to go."
Mir has combined the new diet with a new confidence in his wrestling game, as well.
"Six months ago, I couldn't take my wife off her feet unless I threw some jewelry on the bed," Mir joked, his wife Jennifer sitting at his side. "Other than that, my takedowns were horrible. When people are pushing me against the cage, in the past I was more susceptible to allowing it to happen because I had that jiu-jitsu mentality that I'm not going to grind back. Now I'm learning about head position and I like to grind back. If you're going to push into me, you're not pushing me backward. We're going to go down right here."
And the strength he believes he gave up when he went vegan has returned now that lean meats and other proteins are back in the mix – and now that he's developing other skills in the gym at the same time.
"People are saying to me, 'Oh, you're so much stronger,' " Mir said. "But I think it's that I'm finally using my strength. In the past, I would try to use as little strength as possible because strength will get you tired if you explode too many times. Well, get in shape."
And that's just what Mir believes he had to do. And he said if things go as planned against Nelson on Saturday night, people shouldn't be too hard on his opponent.
"If anybody's going to be on his case and feels that he has a bad performance on Saturday, they've just got to realize that he's facing the best version of me that ever existed, that I ever thought could exist," Mir said.
Mir fights Nelson in the co-main event of UFC 130 at the MGM Grand Garden Arena in Las Vegas on Saturday.