Story highlights At her heaviest, Mia Vayner weighed around 540 pounds

Mia decided to ditch her motorized wheelchair and built a manual sport chair

She now swims two miles every morning and rock climbs regularly

Friends describe Mia Vayner as boisterous, outgoing and passionate. She's not afraid to tell you what she thinks and has a wicked sense of humor.

"Mia is a go-getter," says her wife Evelyn Vayner. "She has lived a life with setback after setback... yet she manages to look at the future and go after what she wants with more vigor and fight than anyone else I have ever known."

That innate drive made Evelyn certain Mia would accomplish her latest goal: to lose more than 250 pounds, despite her paraplegia.

Evelyn met Mia while she was backpacking around Australia in the late 1990s. Mia grew up in the outback and offered to show Evelyn around. Their friendship quickly grew into something more.

"I realized that Mia was transgender and given that I'm from NYC, I truly thought nothing of it," Evelyn says. "I was immediately taken by her openness."

The couple now lives in Flushing, Queens. Mia is a hotel consultant and blogger ; Evelyn works in publishing.

At her heaviest in 2009, Mia weighed close to 540 pounds. Evelyn had also battled obesity her entire life. Late-night binges, empty bags of chips and emotional eating were common in their house.

One day, Mia decided she'd had enough.

"A lot of people think once you're in a wheelchair, you're just nothing," she says. "The doctors said, 'There, there, good fat person.' And I said, 'Screw that.'"

Mia ditched her motorized wheelchair and built a new one from a few broken chairs she got off Craigslist. Her "Frankenchair," as she called it, had a sporty design that allowed her to move more efficiently. She started off slowly -- pushing herself around the block.

In the first month, she lost 50 pounds. By the time she had lost 100 pounds, she was pushing herself a mile every morning.

Evelyn and Mia decided to change their diet, as well. A lifelong vegan, Mia had always eaten good food -- "but you can eat a lot of vegan food." They cut back on portion sizes and started shopping for locally grown, organic produce.

"When we set out to make this change, we knew that it would be a slow road," Evelyn said. "We wanted it to be a slow road because we knew that fast weight loss had always led to ultimate failure."

To keep her goal attainable, Mia told herself she would lose 10 pounds 30 times. She bought a fishbowl and pulled a treat out of it every time she reached another mini-goal. By April 2011 she weighed 325 pounds.

"I do cheat," Mia says. "It's no good saying, 'I'm never going to have chocolate cake again' because your wife will find you on the floor at 3 a.m. with chocolate all over your face."

Mia doesn't like to talk about the incident that left her partially paralyzed below the waist. A physical assault when she was young damaged the nerves in her back, severely weakening her spine. Another accident in her early 40s exacerbated the condition and left her with minimal feeling in her legs.

"I haven't stood up since Bush was president," she likes to joke.

But her disability hasn't stopped her from doing the activities she loves. She does judo from her wheelchair. She swims 2 miles every morning and is thinking about competing in a triathlon.

Mia also loves rock climbing. She and Evelyn joined the NYC Adaptive Climbing group and started climbing two to three times a week at Brooklyn Boulders.

Kareemah Batts, founder of Adaptive Climbing Inc., saw Mia's determination her first day. In the beginning Mia was frustrated that climbing didn't come easily, Batts says, but she wouldn't quit.

"You're fighting with your body to do something that it doesn't do," Batts told Mia.

Mia now weighs 265 pounds and is still losing weight. Her cholesterol and blood pressure levels are normal, and she no longer has type 2 diabetes. She's gone from wearing a size 36 dress to wearing a size 16.

"The weight loss has changed her outlook on life and her self-respect, and also has given her another way to connect with her community," Evelyn says. "It has reinvigorated our mutual interest in all kinds of things we thought were not possible."