title: 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.
  
  
  RESULTS
  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.
authors: Department of Nutrition, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, NC, USA.
authors: Kiyah J
authors: KJ
authors: Duffey
authors: Barry M
authors: BM
authors: Popkin
mesh_terms: D000328:Adult; D000465:Algorithms; D003430:Cross-Sectional Studies; D004326:Drinking; D004435:Eating; D002149:Energy Intake; D005247:Feeding Behavior; D005260:Female; D006801:Humans; D056865:Ideal Body Weight; D008297:Male; D008875:Middle Aged; D009749:Nutrition Surveys; D009765:Obesity / Q000453:epidemiology / Q000517:prevention & control; D011203:Poverty; D014481:United States / Q000453:epidemiology; D016885:United States Department of Agriculture