The energy density of food and drink, portion size, and the number of meals and snacks per day have all been linked to increases in the average daily total energy intake of US adults over the past 30 years, but increases in the number of eating occasions and in portion size have accounted for most of this increase: energy density of food consumed may have actually slightly decreased.

In a study published in this week's PLoS Medicine, Kiyah Duffey and Barry Popkin from the University of North Carolina at Chapel Hill in the USA, analyzed the 24 hour dietary intake in US adults in surveys that carried out between 1977-78, 1989-91, 1994-98, and 2003-06.

The authors found that the average daily total energy intake of one person increased from 1,803 kilocalories (kcal) in 1977-78 to 2,374 kcal in 2003-06, an increase of 570 kcal. Looking at the changes between each survey period, the authors showed that changes in portion size accounted for an annual increase in the daily total energy intake of nearly 15 kcal between 1977-78 and 1989-91, whereas changes in the number of eating occasions accounted for an increase of just 4 kcal. Between 1994-98 and 2003-06, changes in the number of eating occasions accounted for an annual increase in daily total energy intake of 39 kcal, whereas changes in portion size accounted for an annual decrease in daily energy intake of 1 kcal. Changes in the energy density of food and drink accounted for a slight decrease in daily total energy intake over the 30-year study period.

As participants in the surveys may have under or over reported the amount of food consumed, the findings may not be completely accurate but, nevertheless, suggest that efforts to prevent obesity among US adults (and among adults in other developed countries) should focus on reducing the number of meals and snacks people consume during the day and reducing portion size as a way to reduce the energy imbalance caused by recent increases in energy intake.

The authors say: "It is important to note that this is a macro level analysis; these results do not negate the issue of how individual diet and weight change are affected by energy density, portion size, or eating frequency. However, to the extent that all energy intake is equal, and has an equal impact on energy imbalance, this approach to studying changes in energy intake helps guide us to interventions to reduce intake."

Funding: This study was funded by the US National Institutes of Health (R01-CA109831, R01-CA121152), the UNC-CH Clinic Nutrition Research Center (NIH DK56350), and the University of North Carolina. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests: The authors have declared that no competing interests exist.

Citation:
"Energy Density, Portion Size, and Eating Occasions: Contributions to Increased Energy Intake in the United States, 1977-2006."
Duffey KJ, Popkin BM (2011)
PLoS Med 8(6): e1001050. doi:10.1371/journal.pmed.1001050