Many believe the key to losing weight is to exercise more. “That's wrong,” said Lisa Moskovitz, a registered dietician. “When it comes to weight loss, it's usually 80% diet and 20% exercise to achieve your optimal or goal weight.” Moskovitz says popular juice cleanses aren’t always effective. “This cold-pressed organic juice you might think is very healthy, but has almost twice as much sugar as this can of soda,” she explained. Here are a few other diet myths to consider.