Professor Jebb co-leads the Wellcome Trust-funded LEAP project. As a nutrition scientist her research interests are focused on how what we eat affects the risk of gaining weight or becoming obese and the interventions that might be effective to help people lose weight or reduce the risk of obesity-related diseases.

She has also conducted a series of randomised controlled trials to study the impact of dietary changes on the risk factors for cardiovascular disease. In general, this work highlights that body weight is a more important risk factor for ill-health than differences in the nutritional composition of the diet. She has strong scientific collaborations with the Behaviour and Health Research unit at the University of Cambridge and the MRC Human Nutrition Research unit, where she was a Programme Leader for many years.