The purpose of this study was to investigate the relationship between nutrition knowledge and body mass index (BMI). The General Nutrition Questionnaire was distributed to 500 individuals on the database of a large general practice. Results demonstrated that there was no significant correlation between levels of nutrition knowledge and BMI; however, a high level of nutrition knowledge was found among the sample. This suggests that a knowledge deficit may not be the most significant factor preventing overweight individuals from adopting a healthier diet and questions the utility of purely educational approaches to dietary behaviour change. Evidence-based health behaviour change techniques are discussed.