(CNN) -- At work one day, IT consultant Justin Shelton suddenly began to feel ill. A few hours later, he was in the emergency room, and doctors told him he might have a kidney infection.
They just needed to run a scan to confirm the diagnosis.
The next words were a cold reality check: The imaging machine could not support his weight.
"They told me, 'We think you have a kidney infection, but we can't confirm for sure, so we're just going to treat it aggressively and hope that's what it is,' " Shelton said.
He was 25 years old and weighed 592 pounds.
Two years earlier, Justin's wife, Lauren Shelton, had had her own medical scare; her gallbladder had to be removed because of weight-related complications. At her heaviest, Lauren weighed 341 pounds.
Their size made everyday tasks difficult, too. Years ago, Lauren was on a plane, and the seat belt wouldn't buckle. She was mortified and tried to hide from the flight attendants that she didn't fit into the seat.
Both Lauren and Justin had been asked not to get on rides at a theme park because of their size.
But Justin's trip to the emergency room was the final straw. The Jefferson City, Tennessee, couple realized something needed to change.
Luckily for Justin, doctors were right and able to treat his kidney infection without the scan. "It made me think, 'What if it was something else? What if it was more serious? What would I have done then?' " Justin said.
So in February 2012, the couple began a 19-month journey to take control of their health.
"I was always bigger than the other kids, but the pounds really started packing on during high school and continued to do so over the next several years," Lauren wrote on her blog, OvercomingO.com.
For Justin, it was a knee injury at age 13 that kept him from playing sports. The exercise went away, bad eating habits continued, and his weight got out of control.
The Sheltons met online seven years ago, and their relationship revolved around their eating habits. They would go out to eat and indulge in one unhealthy meal after another.
They knew that in order to get healthy, they needed someone to steer them in the right direction. So they sought help from a weight-loss management program at a local medical school.
A physician's assistant gave them guidelines on what they should and should not be eating, and on the amount of exercise they needed.
Justin and Lauren started their new exercise routine by doing simple activities such as walking around the park and swimming. In late 2012, they joined a gym.
"We go to the gym five to six days a week and take one day off and try to do something fun and active like hiking or swimming," Lauren said.
The couple also started using a smartphone app to track the calories they consumed. In the beginning, they ate at restaurants only on special occasions and prepared all meals at home.
Lauren found recipes for healthier versions of the foods they loved. Their diet primarily consists of lean meats with lots of fruits and vegetables. Even today, everything they eat goes into a food journal.
The weight came off quickly at the beginning. Justin lost 25 pounds and Lauren lost 30 pounds during the first month alone. They tried to keep the weight loss steady after that, knowing they couldn't expect to see such a big number month after month without being disappointed.
Weekly weigh-ins helped them track their progress.
"We have graphs that show our weight loss through an app. It helps us stay motivated and get through the hard weeks," Justin said.
In just 19 months, Justin dropped 362 pounds and Lauren lost 176, for a total of 538 pounds.
'Nobody is perfect'
As they begin to move into the maintenance phase of their diet, the couple has allowed themselves to indulge once in a while. They now have what they call their Special Sunday Meal, where they will cook something they don't typically have during the week.
"This Sunday, we may have grilled turkey burgers on a whole-wheat bun with some oven-baked potatoes," Lauren said. "Typically, we do not have starches very often and do not keep breads in the house."
They still give in to cravings from time to time. Lauren says she has a sweet tooth, but she controls cravings by distracting herself with activities such as walks or naps.
What keeps her on track is understanding that "No matter how many times you slipped or messed up, you just have to start over, and eventually you'll get there," she said. "You have to stay positive and remind yourself that you're human and nobody is perfect."
Even though they've managed to lose a substantial amount of weight -- Lauren went from a size 32 dress to a size 12, and Justin went from size 58 pants to a size 36 -- the couple struggles with the psychological side effects of such a massive physical change.
Self-image has been an obstacle for both Lauren and Justin. They admit to having moments when they still see themselves as the obese people they used to be.
"I don't see myself as quite as small as what the pictures show or people tell us we look like," Lauren said.
Through both the struggles and triumphs they have found support in each other. They say that doing this as a team has brought them closer together, and they feel like they are almost newlyweds again.
Recently, Lauren and Justin traveled on a plane and were thrilled to find they could not only buckle their seat belts but needed to tighten them. They also returned to the theme park and rode the rides with no problems at all.
"It was kind of triumphant," Justin said. "We are a lot more adventurous and outgoing. Our outlook has changed almost completely."