When Deputy Scott Stewart joined the Rockdale County Sheriff's Office at age 19, he weighed a lean 180 pounds.

But after 15 years of grabbing fast-food meals and sitting for hours in patrol cars, he had ballooned to nearly 340 pounds and plagued by serious health problems.

"I had to make a lifestyle change," said Stewart, who shed 120 pounds and counting in the past 18 months.

His impressive weight-loss achievement is the product of a simple formula: healthy eating and regular exercise. The trick is staying disciplined, he said. Having a workout partner for his twice-a-day gym visits helps keep him on track.

Weight was not an issue for Stewart until he joined law enforcement, he said.

"It was just being lazy, riding around in a car," he said.

Five years ago, at age 28, Stewart needed back surgery for a herniated disc he attributes partly to being overweight.

"I even put on more weight after that. I was pushing 340 pounds," he recalled.

Health problems piled on, from high blood pressure to sleep apnea-related snoring that regularly woke up his wife Sabrina.

But the catalyst came in May 2012, when the county staged a weight-loss challenge program, offering the winning team of employees an iPad tablet computer. While Stewart's overall team didn't win, "I lost the most weight of everybody," he said -63 pounds.

That motivation turned into momentum.

"I decided to just continue my lifestyle changes," he said.

Healthy eating is a big part of the lifestyle. Stewart drinks at least a gallon of water a day, and only water: "No soda, no sweet tea." He avoids overeating and sticks to healthy choices. Lunch might be a protein shake, some fruit or a lean meat. A Subway restaurant sandwich can be OK.

"You just can't put all the bad stuff on it," Stewart said.

But eating sensibly is only half of the strategy, he said.

"You do have to do some physical fitness, at least an hour a day, five days a week," he said.

Stewart is a regular at Body Tech Fitness Center in Conyers. He hits the gym twice every weekday: once in the morning before work, and again during the lunch hour.

His workout is a combination of cardio and muscle-building. He takes advantage of classes offered by the fitness center, such as kickboxing.

If working out twice a day sounds tough, that's because it is.

Stewart wakes up at 5 a.m. to squeeze in his morning exercise time. His secret weapon in the fight for motivation is a workout partner.

Allen Wright, an investigator assistant at the Sheriff's Department, joins Stewart at the gym. Wright is having great weight-loss success of his own, dropping 95 pounds.

"It's a good symbiotic relationship," said Wright. He explained that when one of them doesn't want to hit the gym, the other one is there to push, "and you just do it."

"It just makes things easier when you have a buddy system," said Stewart.

Determination is important for long-term weight loss. Stewart noted that at first, people will lose weight quickly, but then the body reaches a point where it takes much longer to work off the pounds. After dropping 5 pounds a week early in his effort, Stewart is now at that point himself.

"I'm still struggling with it because it doesn't happen as fast," he said.

But Stewart is already seeing great benefits from weight loss so dramatic that people who hadn't seen him since last year don't recognize him.

His health issues have lessened or disappeared. His wife "likes that I'm in better shape." He finished third in a field of over 2,000 in this year's "Fuzz Run," a 5K fund-raiser footrace in Covington.

The slimmer, trimmer Stewart is also much better at another kind of footrace - pursuing suspects on the job.

"I've chased numerous people and caught them," he said.