Aim Analyses of changes in food choice patterns made during weight loss may be informative for practice. In this research, food categorisation may be critical. The aim of the present study was to identify key changes in food choice patterns in weight loss trials. Methods Changes in dietary patterns between baseline and three months were analysed for 231 participants from two weight loss trials in terms of grams of food, kilojoules and the number of food serves consumed. Two food categorisation systems were applied using six more traditional food groups and 17 newly defined food categories considering national food guidance systems, and specific criteria, including the scientific evidence on the relationships between consumption of specific foods and health outcomes associated with weight management. Results After three months, there was no significant change in the total weight of food consumed, yet mean energy intakes decreased by more than 3000 kJ. Where six categories were applied, all groups except milk and milk alternatives were altered by the diet prescription. However, with 17 categories, subtle changes were more clearly demonstrated. For example, the 17 categories showed increased intake of low-fat dairy foods and decreased intake of fatty meats, non-wholegrain (refined) cereals specifically, and non-core foods and drinks more broadly. Conclusions Changes in food choice patterns can be identified during weight loss trials. Applying a greater number of categories in the analysis enables a greater identification of changes in choice of key foods reflecting actual dietary change.