Moncks Corner, South Carolina (CNN) -- Bryan Ganey slowly climbed out of his parents' car. Michael and Martha Ganey had driven their son to work because he wasn't feeling well -- for the past couple of days, simple tasks had left him short of breath and exhausted.

At 577 pounds, being out of shape was normal for Bryan, so he ignored it. But as he headed toward the door of his office on June 20, 2010, the ground suddenly shifted.

The Ganeys were pulling away when Martha's cell phone rang. All she heard on the other end was gasping.

The couple stopped the car and sprinted back to the building, where they found their son lying in the bushes, struggling to breathe. The ride to the hospital took only five minutes, but to Martha, it seemed like hours. Bryan didn't care how long it took -- he knew he was going to die.

"I was absolutely convinced that I was having a heart attack. I had been told by doctors before that at my size, if I ever had heart problems, they weren't going to be able to operate on me. So there was a very good chance that this was the end -- that I would get there and there wouldn't be anything they could do," he said.

Out of control

For years, Bryan worked the night shift at a Verizon call center in Charleston, South Carolina, 20 miles from his home in Moncks Corner.

He skipped breakfast, ate fast food for lunch and dinner, then picked up a pizza or some convenience store snacks on his way home. He often drank more than a gallon of soda a day. By the age of 37, he had a body mass index around 87. A BMI over 30 is considered obese.

"He was very aware that he had a problem," Martha said. "It was out of control."

June 20 was possibly the best thing that could have happened to Bryan, although it certainly didn't seem like it at the time. His "heart attack" was actually a pulmonary embolism, or a blood clot that had traveled to his lungs, blocking his oxygen flow. According to the Centers for Disease Control and Prevention, "sudden death is the first symptom" in about a quarter of patients who have a pulmonary embolism.

For six days, Bryan lay in a hospital bed, covered in bruises caused by the blood thinners being pumped into his body. The blood thinners slowly cleared the blockage in his lungs, giving him plenty of time to think.

"At first, I felt like a victim, like somebody or something had done this to me," Bryan said in a YouTube video about his experience. "But then reality set in and the pain turned to anger. My condition was unacceptable."

Several doctors tried to broach the subject of weight-loss surgery while he was in the hospital, but Bryan refused. Both he and his mother had friends who had gone through the surgery and were suffering from complications.

If I can make it out of here alive, he thought, I'm not coming back.

Small steps

Today, Bryan, 39, tells his story from the driver's seat of a car that he wouldn't have fit in two years ago . He shops for clothes at department stores, buys one seat on an airplane instead of two and sleeps through the night.

"The absolute best thing about all the weight that I've lost is just waking up every day and realizing that I don't weigh 577 pounds anymore," he said with a laugh. "The biggest rewards are the smallest ones."

Small steps are what began Bryan's weight loss journey. After leaving the hospital, he began to move -- at first pushing a shopping cart around the grocery store like a toddler learning to walk. Then he ventured to the mailbox at the end of his driveway. Soon, he was conquering several miles at a time.

He lost 130 pounds in the first six months, then dropped another 140 pounds over the course of the next year. At 5-foot-8, Bryan now weighs just under 300 pounds.

"It turns out it really is true," Bryan wrote in his iReport submission. "If you use more energy than you take in, you will lose weight."

Bryan switched to a day shift at work to conquer his bad eating habits. He's very particular about what he puts in his mouth, refusing to stray from self-prepared lean meats, vegetables and fruits. He eats five to six meals a day, every two to three hours. He measures his portions so that his total calorie count for the day hits 2,500.

"Food is everywhere," he said, reflecting on his struggles to keep on track at work or in social settings. "I just can't eat it anymore. I can't do it ever again. I don't have the ability to have just a little bit. They think I must be miserable because I ... don't allow myself to have certain things. [But] the benefits I have gained, the prize is worth the struggle."

After dropping his first 70 pounds, Bryan decided to hire a personal trainer. This wasn't the first time he had tried to lose weight by exercising, and in the past he had burned himself out pushing too hard, too fast. His trainer, Martha Peake, started slowly. At first, all they did was sit down and stand up. For the 500-pound Bryan, that was enough.

Last year, Bryan limped across the finish line of the 10K race he entered. This year, he plans to run the whole race. He's still losing six to seven pounds a month and hopes to eventually get down to 200 pounds.

Simple prayers

Every morning, Martha wakes up and asks God to give Bryan one more day. She understands the obstacles placed before her son -- most addicts can give up their abusive substance, but he can't just give up food.

"I guess there's always that little shadow of a doubt," Martha said. "But I know also that he's a very strong person ... if it can be done, he can do it."

When Bryan returned to the doctor, the change in his blood work was almost unbelievable. He's off many of the medications he was on before; his blood pressure medication has been cut four times over the last two years. His LDL cholesterol, the bad kind, is 100 -- an optimal number.

Most importantly, at 577 pounds, Bryan was prediabetic. Now, he's looking forward to a bright, diabetes-free future.

"I think what gets lost in the advertisements and everything that's written about weight loss is that if people would keep it simple, that everyone has that power in them. You can change your life."