Aimee Smith of Janesville, Wis., knew she was big, but since her scale only registered 300 pounds, she didn't realize how big. She finally weighed herself one day and was shocked to see the real number - 427 pounds.

"My knees hurt, my back hurt. I had high blood pressure. I was pre-diabetic. I was going down a bad path," she says. "I'm sure carrying around 400 pounds wasn't doing my health any favors."

That was a little over two years ago. Since then she's had gastric bypass surgery, completely overhauled her lifestyle and lost more than 200 pounds - half her body weight. Now she competes in triathlons and runs 10Ks. She's training for the Wisconsin marathon this upcoming May. Eventually, she'd like to do an Iron Man triathlon.

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"In high school I probably would have been voted least likely to do something athletic if there was such an award," she says with a laugh. "I've lost so much weight that when I went back for my 25 th reunion recently, no one recognized me. They thought my husband was the one who was in their class!"

Smith, 44, has some sage advice for anyone contemplating a similar weight-loss journey.

"You've got to change your relationship with food. Start thinking of it as fuel rather than a friend you can rush to whenever you're having an emotional problem," she says.

Smith admits that some fuels tastes better than others but once she began working with a health coach who helped her commit to a healthier way of eating, the weight really started coming off. She's learned to embrace fruits and vegetables, even "exotic" picks like kale and collard greens which she says were completely foreign fare in her previous life.

She still splurges on the occasional cookie but instead of buying a huge bag of processed junk, she goes to a local bakery or coffee shop and orders just one.

"I then can enjoy the one item - it's been very liberating to not be so tied to food," she says.

Regular exercise has also been a huge factor in her weight loss. After having surgery, she signed up for a "couch to 5k" program and took it twice. She learned to swim so she could enter triathlons. Now she loves to compete even though she usually finishes at the very back of the pack.

She's serious about training and racing but she tries to have fun with it. For her last 10K she wore a tutu and a Santa hat and kept stopping to pose for pictures.

Nothing in Smith's formula is an earth-shattering secret, but research suggests her approach is on the right track. For example, the National Weight Control Registry, which tracks successful "losers" who've dropped an average of 66 pounds and kept it off for more than five years, found 98 percent of registrants overhauled their eating habits and 94 percent increased physical activity.

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Registrants also reported relying on social support, something Smith says has been important to her. Her husband, kids and co-workers have been there to cheer her from the very first shed pound but she says one of the biggest surprises is how much encouragement she's gotten from the athletic community.

"These are serious athletes who stand on the podium at the end of a race. I expected them to be snobs. But it's been very eye-opening how compassionate they've been towards me. They love my determination and they go out of their way to let me know they're proud of me for not quitting," Smith says.

Has the long process of weight loss been discouraging at times? Sure. Especially, Smith says, because she started off with hundreds of pounds to lose.

"It's not always helpful to look at the big picture," she says. "Start small and if you can only do two steps at a time, do that and then do it again tomorrow. Progressively build on what you can."