Background Online health information seeking using social questions and answers (Social Q&A) sites has been increasingly popular in recent years. It calls for better understanding of health information seeking behaviour and interactions between information seekers and information providers. Objectives The study investigates how diet information seekers interact with information providers on WebMD Answers, which is a Social Q&A site devoted to health-related topics, and examines the factors that constitute a ‘helpful’ answer from an information seeker's perspective.