Here's why UFC fighter Ronda Rousey gained weight to be in the Sports Illustrated swimsuit issue

Mixed martial arts fighter Ronda Rousey, 28, is most well known as the first and current UFC Women's Bantamweight Champion.

In 2012, she appeared on the cover of ESPN The Magazine's annual Body Issue.

And just last week Rousey made her debut in the pages of the Sports Illustrated swimsuit issue.

But getting into shape for the ESPN magazine and Sports Illustrated were very different processes. Rousey explains to USA Today:

The ESPN Body Issue is about celebrating the peak of human potential and the kind of form the human body, when specialized, can really look lik. The Swimsuit Issue has a lot more [of a] sexual side to it, while I don't think the Body Issue is overtly sexual whereas Sports Illustrated is.

The difference in how I approached it is when I posed for ESPN Body, I really tried to be a lot more cut and a lot more close to my prime fighting shape because I was being photographed as a fighter and trying to look more like a fighter.

I purposely tried to get a little bit heavier for the SI issue so I was a little bit curvier and not in top fight shape look but the look at which I feel I'm the most attractive. It's very natural for a person's body to go through seasons.

Rousey is no stranger to gaining and losing weight quickly.

In order to maintain 135 pounds, the weight limit for the women's bantamweight division, Rousey must make sure she's not a pound over when it's time to fight.

To ensure she'll make weight, Rousey explained to the New Yorker that she goes on an incredibly salty diet for a week so that her body bloats. Then when the fight is close, she removes all salt from her diet so her body lets go of all of that fluid with the help of a steam room.

Before a fight in February 2014, a typical breakfast for Rousey was eggs, turkey bacon, and spinach with a lot of pink Himalayan salt.

Before Rousey became the first female UFC fighter, she went to the Beijing Olympics in 2008 for judo.

She won a bronze medal.

When Rousey returned home, she had no job to fall back on. "There's nothing put in place for Olympians after they're done. They give you a couple grand, a handshake and they kick your ass out the door," she told MTV.

Rousey was forced to take a graveyard shift at a 24 Hour Fitness in California while trying to figure out what she wanted to do.

In 2010, she returned to fighting at an MMA gym in Los Angeles. In just seven months, she went from an out-of-work ex-Olympian to a professional MMA fighter, winning her first fight in 25 seconds.

When the league she worked for, Strikeforce, announced it would shut down in 2013, the UFC scooped her up immediately, making her its first female fighter ever. CEO Dana White, who previously vowed to never employ a female fighter, said, "I think she's going to be a big superstar."

Since then, Rousey has made the sport mainstream in a way it had never been before and opened the door for more female fighters to join UFC.

She has over a million Instagram followers.

And has dabbled in modeling, appearing in a current campaign for Buffalo jeans.

But now, she also has her sights set on acting.

In 2014, Rousey made her major motion picture debut in "Expendables 3."

This year, she will appear in "Furious 7" and play herself in the upcoming "Entourage" movie.

"I'll keep fighting and filming together. Having them both allows me to do each one longer," she tells USA Today. "I'm able to step away from one and allow myself to miss the other. I've found an amazing balance. I'm always happy and engaged and motivated."

Rousey adds that creating new goals for herself keeps her motivated.

I love fighting and it's my passion and it's the reason Hollywood took an interest in me at all, but I'm no dummy. I know there's a short shelf life in the sport and I don't want to be left out like I was after the Olympics [she won a bronze medal in judo at the 2008 Games in Beijing] with no options. I need to have a new grand goal to go after because when I have no goal is when I get depressed and I'm not letting that happen again.

I set extremely high goals for myself. The first day I stepped onto a judo mat I was like 'I'm winning the Olympics,'" she said. "The first day I did MMA, 'I'm winning the UFC.' The first time I had an acting gig, I said 'I want to be the highest-grossing actor in the world.' That's what my goal is.