Determination of energy density of freely selected diets: methodological issues and implications

BACKGROUND: There is increasing evidence that dietary energy density (ED, k J/g) may be an important dietary characteristic, particularly in respect to control of energy intake; however, there are no agreed methods for derivin g the ED of freely selected diets, and ED values may be markedly affected b y the inclusion or exclusion of specific dietary items, particularly bevera ges. OBJECTIVE: To highlight the consequences of using six different methods of ED calculation, and their implications for characterizing differences betwe en weight status groups and identifying associations of ED with macronutrie nt intakes. DESIGN: ED was calculated using six defined methods: (1) all food and bever ages; (2) all food and energy beverages; (3) food, milk and alcohol; (4) fo od only; (5) all dry matter; (6) protein, carbohydrate and fat only, of var ying exclusions of different beverages and water. For illustrative purposes , data from 41 lean (LE, body mass index (BMI) 20 - 25 kg/m(2)) and 34 obes e (OB, BMI greater than or equal to 30 kg/m(2)) adults who kept 4-day weigh ed dietary intake records are described. RESULTS: ED values (and coefficient of variation, CV) differed substantiall y by methods of calculation. OB reported significantly greater mean ED comp ared with LE by one method (all food, milk and alcohol, excluding other non alcoholic beverages); however, the opposite was found using another method (dry weight). For most calculation methods, ED was negatively associated wi th percentage energy from carbohydrate for LE, in contrast to OB. All metho ds found positive correlations for ED and fat (g) among LE, but only one me thod found such a correlation among OB. Similarly, three methods produced p ositive correlations between ED and percentage energy fat amongst LE; howev er, this was only observed amongst OB with one method. CONCLUSIONS: Methods of calculating ED of freely selected diets must be car efully defined, and can markedly influence apparent relationships of ED wit h other dietary measures and subject characteristics.