Scientists are trying to develop high-tech monitoring devices to help obese people who want to change face the truth about their habits.
The experimental devices are designed to keep track of how many minutes overweight or obese people work out, how much they eat and even whether they are at a fast-food joint when they should be in the park.
Traditional weight-loss interventions rely mainly on people's memories but researchers have long known that method can be unreliable since people often forget details or lie.
In a lab in a Los Angeles suburb, two overweight teenagers help test the devices by taking turns sitting, standing, lying down, running on a treadmill and playing Wii. Wireless sensors on their chests record information and send it to a cell phone.