The following is one of a series of weight loss success stories featured on Mother Nature Network. Check back for more in coming weeks.

If anyone could say they were too busy to lose weight, it’s Ryan Stewart.

This 33-year-old father of four works as an elementary school and sixth-grade teacher, serves as camp director for a Boy Scout summer camp, takes on tutoring jobs on the side and volunteers as a Sunday school teacher at his church.

And, as if his load weren’t heavy enough, Stewart was taking grad school courses when he decided to start dieting and exercising.

“I was trying to juggle life on top of grading papers and all that other stuff,” he said.

But last spring an opportunity came along that stoked Stewart’s competitive spirit and spurred him to lose more than 45 pounds: members of his church organized a “Biggest Loser” contest.

For Stewart, it was a chance to shed some weight while indulging in a little good-natured rivalry with his friends and family. (His wife also joined the competition.)

He recalled saying to himself, “I’m gonna win this.”

But it wasn’t just bragging rights at stake: the winner received $400 and second place got $250.

Stewart said that when the competition began in March, he weighed 220 pounds and “was starting to feel it.” In particular, the weight made him feel more tired and caused him to have less energy.

For the contest, Stewart said he wasn’t too strict with his diet but he made some significant changes, including cutting out as many desserts as possible. In addition, he said he changed portion sizes, included more healthy fare and started taking only one helping of food instead of his usual two or three.

The biggest lifestyle change came with running: Stewart said he had never really exercised in his life. “It was kind of a joke in my family,” he said.

And so, for the first two or three weeks, he could barely eke out a mile. But by the end of the contest in May, he could go as high as four miles a session. On average, he said, he ran between one and three miles, four times a week.

To keep the contest fun, Stewart and a friend who also was competing liked to goad each other by sending one another bags of M&Ms.

But Stewart would ultimately have the last laugh: he won the contest and took home the $400 prize.

He continues to lead a busy life, but he’s managed to keep the weight off and seems confident about the future.

“I’ve developed some habits that are much better,” he said. “I’m not pigging out like I used to.”

Jillian Michaels would be proud.