Transcript for Dieting Website Has Users Bet to Lose, in Order to Win
In a country obsessed with losing weight, tonight a novel and controversial approach. It involves combining dieting with gambling. I'm not making this you have. There is a real company that will bet you that you cannot lose weight. And if you succeed, you can make thousands of dollars. So is this the future of dieting, or is it just trading one addiction for another? Here's ABC's linsey Davis. What do you guys think? Beautiful. Reporter: When you're a size 14 -- The dress is on. Reporter: -- The thought of standing next to a bride who looks like this can be daunting. My hips are too big. Reporter: But Christina Maher is up to the challenge. I'd really like to be a size 10. Cross my fingers. Reporter: To shed all those pounds Christina is quite literally putting her money where her mouth is. I started the diet bet three months ago. Reporter: Each month she pays $385 to healthy wage, a company that allows you to place a bet that you can lose the weight. The wager -- if she loses 40 pounds in six months, she'll win $5,000 plus get all her money back for a grand total of $7,310. I am now down 20 pounds, which is great. And so I have another 20 to go. You have a goal. Reporter: But if Christina doesn't lose the weight, she's out thousands of dollars. I really need to get myself into gear so I can win this bet because I cannot afford not to. Reporter: With all her money on the line, this could be just the ultimate motivation to shed the pounds. But can she do it? According to studies, people using money as a motivator are five times more likely to reach their goal weight. Could this be the future of dieting? Betting for weight loss is like betting on your retirement at caesars. Reporter: Not according to Dave zinzanko, fitness expert and author of "Eat it to beat it." People go on these short-term like diet crashes and then they immediately want to reward themselves at end of it and they do that with a bag of oreos. Reporter: Healthy wage says it's already paid out more than $2 million in prize money. Yet only 1/3 of participants actually win their bets. In our view there's always a win somewhere. I mean, the people who -- the number of people who make a bet and then just fall off the radar are very few. Almost everyone loses some weight. The question is are you going to accomplish your goal? Reporter: Christina's hoping she can beat the odds and actually win. Her weight has been a lifelong struggle. I remember being 6 years old and thinking that I was overweight. I got on a scale and thinking I was fat. Reporter: At her heaviest she was 295 pounds. You tried everything. Everything that you can imagine. I almost feel like I'm such an expert on losing weight. It's just the actual follow-through that I, you know, struggled with over the years. Reporter: After a promising start two months after the trip to the bridal salon Christina's only dropped eight pounds. I have another 12 pounds. I need to be 194 pounds to win the bet. And how much time do you have to go? I have a little bit more than a month. Reporter: But she's fallen off the wagon a few times. I'd have a cookie. And then I'd have a whole package of cookies or I would eat an entire pint of ice cream. Reporter: So with just one month to go, Christina has to kick her diet into high gear, eating only 1,600 calories a day. I literally weigh to the gram of pretty much everything. Reporter: She opts to track her weight online by recording every calorie she consumes. And tracks every step she takes with a fit bit. I have 4,034 steps right now. Reporter: The weight is coming off. I used to wear this as a shirt. Now it comes down to almost my knees. Reporter: But as far as she's come, it may not be enough. 206.8. It's a little bit higher than it was yesterday. Reporter: But can Christina lose enough in time to win the bet? Remember, more than $7,000 is on the line. Two weeks later, Christina is riding high. She lost 34 pounds in 5 1/2 months. I've been going a little low carb and a little bit lower calorie. So now I'm eating closer to 1,200, 1,300. Reporter: Restricting her calorie intake, Christina has scaled back her workouts. That's why I've been walking in the park a lot and getting in as many steps as possible. Reporter: And powers through her hunger pains. For now it's still fruit and water. What's the first thing you're going to eat when the bet is over? A slice of pizza and a piece of ice cream cake. Reporter: Four days later, the moment of truth. She weighs in at 193 pounds, winning the bet with one pound to spare. What did it feel like when you stepped on that scale? Relief. And excitement. Looking at the scale and seeing my progress, I couldn't believe it. And I was so happy. Reporter: Christina's weigh-ins were all self-reported, which means healthy wage is taking her at her word. You couldn't really just rely on somebody's video. Maybe they cheated the scale somehow. We're pretty good at detecting cheaters and making sure that everybody is actually losing weight and not trying to cheat and get money. Reporter: We met up with Christina a few weeks later at the gym, and healthy wage is also here to hand-deliver her winnings. You won your bet. So here's your check from us to you for $7,300. All the work that I did for this money, it's -- this is really big. Reporter: But three weeks after reaching her hard-earned goal of 194 pounds she gets back on the scale. The number isn't pretty. What does it say? 211. So it's what, 16 pounds -- 16 pounds in about three-plus weeks. Reporter: Gaining back more than a third of her weight loss in just a few weeks. Short-term solutions are never the best solutions. You want a plan that helps you be successful over the long haul. Reporter: Although they don't tell you what to eat, healthy wage says they do offer guidance and support. Obviously we can't control people but our content and all our motivational tips and e-mails all revolve around losing weight in a consistent long-term way. Reporter: But despite her weight gain Christina says she isn't worried. It's going to be fine. It's going to be back in no time. I'm sure of it. I'm betting on you. Reporter: For "Nightline" I'm linsey Davis in New York.
This transcript has been automatically generated and may not be 100% accurate.