Choosing the best method to estimate the energy density of a population using food purchase data.

Background
Energy density (ED) is a measure of the energy content of a food component or diet relative to a standard unit of weight. Widespread variation in ED assessment methodologies exist. The present study aimed to explore the feasibility of calculating the ED of the Scottish diet using UK food purchase survey data and to identify the most appropriate method for calculating ED for use in the development of a Scottish Dietary Goal that captures any socioeconomic differences.

Methods
Energy density was calculated using five different methods [food; food and milk; food, milk and energy containing (non-alcoholic) beverages; food, milk and all non-alcoholic beverages; and all food and beverages]. ED of the Scottish diet was estimated for each of the ED methods and data were examined by deprivation category.

Results
Mean ED varied from 409 to 847 kJ 100 g–1 depending on the method used. ED values calculated from food (847 kJ 100 g–1) and food and milk (718 kJ 100 g–1) were most comparable to other published data, with the latter being a more accurate reflection of all food consumed. For these two methods, there was a significant gradient between the most and least deprived quintiles (892–807 and 737–696 kJ 100 g–1 for food and food and milk, respectively).

Conclusions
Because the World Cancer Research Fund recommendations are based on ED from food and milk, it was considered prudent to use this method for policy purposes and for future monitoring work of the Scottish Diet to ensure consistency of reporting and comparability with other published studies.