It's a classic trick once thought to aid in weight-loss efforts. But a new study reveals it actually might undermine your fitness goals.

In an effort to lose weight, many folks will post a picture of their ideal body in a conspicuous place like the fridge door or on the bathroom mirror. The idea is that the photo will motivate you to skip the snack in the fridge or to head out to your next workout.

But a recent study has found that these images might be far from motivational. In fact, they might cause you to gain rather than lose weight.

For the study, conducted at Tilburg University in the Netherlands, researchers evaluated female volunteers who signed up for a weight-loss program. As part of their program, the women were given diaries in which to keep a food journal. But here's the catch -- half of the women got a diary that featured a skinny model on the cover and on every page. The other half got diaries with the neutral image of a logo.

The results might surprise you. Unlike the women with the neutral journals, the women with skinny models on their dairies did not lose weight. They actually gained weight.

Even though both groups started out strong in their weight-loss programs, the women who saw the skinny model each time they wrote in their food journals were much more likely to break their diet and start sneaking snacks.

According to the study's authors, frequent exposure to images of skinny models "changes the dieter's belief about the very attainability of a thinner self. Our findings reveal that the perception that a goal is unattainable demotivates dieters from investing effort in achieving the goal and causes them to disengage from the goal."