Nutrition knowledge was assessed using the validated General Nutrition Knowledge Questionnaire which included four domains (1) advice from health experts (11 items, e.g. which fat do experts say is most important to cut down on?), (2) food groups and food sources (71 items, e.g. are these foods high in salt?), (3) food choice (12 items, e.g. what is the best choice for a low-fat, high fibre snack?) and (4) diet–disease relationships (22 items, e.g. what major health prob- lems are related to a low fibre intake?) (Parmenter and Wardle, 1999). Nine questions were modified to include recent evidence in nutrition knowledge (e.g. what health problems are related to excess sugar?). Food items were altered to increase participants' understanding (e.g. orange juice instead of orange squash).
Participants were asked to complete all questions. Each correct an- swer scored 1. Incorrect and missing values scored 0. Subscale scores were calculated for each domain. The sum of the four sections was cal- culated to give a maximum potential score of 116. The overall nutrition knowledge score was divided into quintiles. Participants in quintile 5 scored highest for nutrition knowledge.