(Image Credit: Courtesy Heather Wajer)

When Heather Wajer was 22, her mother was diagnosed with ALS, a degenerative nerve disease that generally leads to paralysis and then death.

For Wajer, the news was devastating. She moved in with her mother, becoming the woman's full-time caregiver for three years until her death.

Seeing her mother, a vibrant woman who was her best friend, fade away from what's also known as Lou Gehrig's disease took an enormous toll on Wajer.

"I used food to cope," Wajer, who just relocated to Austin from California, said in an interview that aired today on "Good Morning America." "You know, some people use drugs. I used food and alcohol to cope with what was going on with her because. I didn't have a lot of joy in my life. And so I would just eat to make those feelings go away.

"After my mom passed away, you know, I continued living that way. And five years later I woke up and I was, you know, over 300 pounds. I was drinking every day, smoking a pack of cigarettes a day. And I didn't really know how I had gotten there," she said.

Wajer's Wake-Up Call

At her heaviest, Wajer, who's 5-foot-7 inches, tipped the scale at 315 pounds.

One night, after drinking "too many glasses of wine," Wajer, who was now a mother, passed out on the sofa. Her son, Griffin, was frightened.

"And I woke up with him sitting next to me, shaking me, saying, 'Mom, mom.' And I looked at him. And he was 3 years old. And I was just lying on the couch, unconscious. And he was scared. And he didn't know what had happened. [At] that moment, I realized that I really needed to change my life for him," she recalled.

She did. Slowly but surely, Wajer lost more than 150 pounds. She's now an Ironman triathlete, and headed to Kona, Hawaii, after winning a coveted spot in the Ironman World Championships being held there Oct. 13.

The Ironman Triathlon is a grueling annual event during which competitors must do a 2.4 mile swim, a 112-mile bike race and a 26.2-mile marathon run, all within 17 hours.

Wajer's remarkable transformation began with a friendly wager with a co-worker who also was overweight. They wanted to see who could be the first to lose 40 pounds. It was intended just to support each other's weight loss goals, but it got Wajer moving.

She and a few co-workers signed up for a sprint triathlon so they would be motivated to get up and exercise every day.

"We had the time of our lives," she said. "And it changed all of our lives in some way. We didn't all become Ironmen. But it changed all of our lives for the better."

Another Profound Change

When she first started training for triathlons, someone gave her a DVD about the Ironman competition.

The DVD profiled 33-year-old Jon Blais, an Ironman competitor who had been diagnosed with ALS.

The profile detailed how Blais, who had already started to lose feeling in his fingers and feet, completed the Ironman World Championships. He had pledged to do so no matter what happened.

Blais, of Massachusetts, finished the race with about 30 minutes to spare. Physically and mentally exhausted, Blais - known as Blazeman - log-rolled himself across the finish line in Kona.

"And I sat there just bawling, watching this because obviously I had lost my mom," Wajer said. "And I knew how hard it was for him. Not physically even so much as mentally. It just was one of the most inspiring things I've ever seen. And that day I decided I wanted to do an Ironman because if he could do it with ALS, then I could do it."

Wajer joined the Blazeman Foundation to raise awareness for ALS. Jon Blais died in 2007 at the age of 35 and his parents formed the foundation in his memory.

'I Never Will Be a Skinny Person'

Wajer's turnaround affects every aspect of her life. She eats high-quality nutritious food, but allows herself some less-than-healthy treats now and then.

"You know, I'm not a skinny person. And I never will be a skinny person. And that's OK," she said, adding that her weight fluctuates between 157 and 167 pounds.

Her son, Griffin, 8, is now a mini-triathlete who trains with her.

Wajer's focus is on remaining healthy and strong, and she had some advice for people who are facing their own weight problems: "You don't have to stay stuck. I think a lot of people feel stuck. I know I did. When I was 315 pounds and drinking every day, I didn't know how to stop those behaviors. I didn't know how to stop any of that. I felt very stuck."

What worked for her, she said, was starting out small. Small changes became big changes, she said.

"I didn't start out by saying to myself, 'I want to lose 150 pounds.' And 'I want to do an Ironman triathlon.' I started out by saying, 'I want to be able to walk around the block. I want to be able to lose 10 pounds.'

"If you put one foot in front of the other, you can accomplish anything. When I look back on the past five years, it's amazing to me what I've accomplished. You don't have to stay stuck in whatever small life you want. You can create the life that you want. Whatever that looks like."