Sister and brother Emma and Matthew from Camberley in Surrey are under the spotlight this time. Matthew is very sporty, mountain-biking at weekends and going to the gym three times a week, while Emma restricts her food intake on weekdays to just a few hundred calories a day. So why are these two putting on weight? They're convinced they're making the right choices with their food, but Emma's habit of picking while cooking, and Matthew's willingness to indulge in chocolate cake immediately after exercise, seem to suggest otherwise. Once they learn the shocking truth of what they're really eating, will these siblings be able to stick to a healthy eating plan, start winning their fight with the flab and look forward to a healthier future?