Energy density, portion size, and eating occasions: contributions to increased energy intake in the United States, 1977-2006

Abstract

Background: Competing theories attempt to explain changes in total energy (TE) intake; however, a rigorous, comprehensive examination of these explanations has not been undertaken. Our objective was to examine the relative contribution of energy density (ED), portion size (PS), and the number of eating/drinking occasions (EOs) to changes in daily TE.

Methods and findings: Using cross-sectional nationally representative data from the Nationwide Food Consumption Survey (1977-78), Continuing Survey of Food Intakes of Individuals (1989-91), and National Health and Nutrition Examination Surveys (1994-98 and 2003-06) for adults (aged ≥19 y), we mathematically decompose TE (kcal/d) to understand the relative contributions of each component-PS (grams/EO), ED (kcal/g/EO) and EO(number)-to changes in TE over time. There was an increase in TE intake (+570 kcal/d) and the number of daily EOs (+1.1) between 1977-78 and 2003-06. The average PS increased between 1977-78 and 1994-98, then dropped slightly between 1994-98 and 2003-06, while the average ED remained steady between 1977-78 and 1989-91, then declined slightly between 1989-91 and 1994-98. Estimates from the decomposition statistical models suggest that between 1977-78 and 1989-91, annualized changes in PS contributed nearly 15 kcal/d/y to increases in TE, while changes in EO accounted for just 4 kcal/d/y. Between 1994-98 and 2003-06 changes in EO accounted for 39 kcal/d/y of increase and changes in PS accounted for 1 kcal/d/y of decline in the annualized change in TE.

Conclusions: While all three components have contributed to some extent to 30-y changes in TE, changes in EO and PS have accounted for most of the change. These findings suggest a new focus for efforts to reduce energy imbalances in US adults.

Figure 1. Average portion size and energy density per eating occasion, by food and beverage.

Data on PS (A) and ED (B) are from cross-sectional nationally representative samples of adults (≥19 y) taken from NFCS 1977–78 (n = 17,464), CSFII 1989–91 (n = 8,340) and 1994–98 (n = 9,460), and NHANES 2003–06 (n = 9,490), standardized to the age, gender, and race/ethnic distribution of the sample in 1977–78.

Figure 2. Annualized contribution of portion size, energy density, and eating occasions to total energy intake changes.

Values represent the annualized energy contribution (kcal) of changes in the number of EOs, PS, or ED of each EO to changes in total daily energy intake (kcal). Data are from cross-sectional nationally representative samples of adults (≥19 y) taken from NFCS 1977–78 (n = 17,464), CSFII 1989–91 (n = 8,340) and 1994–98 (n = 9,460), and NHANES 2003–06 (n = 9,490), standardized to the age, gender, and race/ethnic distribution of the sample in 1977–78.