The demand for clinical trials targeting lifestyle intervention has increased as a result of the escalation in obesity, diabetes mellitus and cardiovascular disease. Little is published about the strategies that dietitians have used to successfully screen potential study volunteers, implement interventions and maximise adherence and retention in large multicentre National Institutes of Health funded nutrition and lifestyle intervention clinical trials. This paper discusses an expanded role for the contributions of dietitians as members of an interdisciplinary team based on research experiences in the Diabetes Control and Complications Trial, Diabetes Prevention Program and Look AHEAD (Action for Health in Diabetes). Many of the strategies and insights discussed are also relevant to effective clinical practice. Dietitians need to broaden their scope of practice so that they are integrated proactively into the screening and intervention phases of large clinical trials to maximise retention and adherence to assigned nutrition, lifestyle and behavioural interventions. The skills of dietitians are a unique fit for this work and it is important that investigators and project managers consider including them in both the screening and intervention phases of such clinical trials to maximise retention results.