In a new study published in the online publication PLoS Medicine, the researchers examined US population and dietary data dating back to 1977 to understand the relative contributions of energy density of foods, number of eating occasions, and portion sizes to energy intake over time. They found that average total daily energy intake increased from about 1,803 calories in 1977–78 to 2,374 calories in 2003–06, an increase of 571 calories.
Changes in the energy density of foods slightly decreased over the 30-year period – but the researchers estimated that about 15 calories a day were added due to increased portion sizes between 1977-1978 and 1989-1991, while more eating occasions added 4 calories a day. However, between 1994–98 and 2003–06, more meals and snacks accounted for an extra 39 calories a day, while portion size appeared to level off, leading to a decrease of about 1 calorie a day. Over the 30-year period, the average number of daily eating occasions increased from 3.8 per day to 4.9.
Dr. Barry Popkin, the study’s senior author and professor of nutrition at the UNC Gillings School of Global Public Health said: “First, the food industry started ‘super sizing’ our portions, then snacking occasions increased and we were convinced we needed to drink constantly to be hydrated. This study shows how this epidemic has crept up on us. The negative changes in diet, activity and obesity continue and are leading to explosions in health-care costs and are leading us to become a less healthy society.”
According to the Centers for Disease Control and Prevention, more than one-third of US adults and 17 percent of US children are obese – and from 1980 to 2008, obesity rates doubled for adults and tripled for children.
Popkin cautioned that under- or over-reporting by study participants of the amount of food they consumed could mean there are inaccuracies in the data.
“Still, these findings suggest that efforts to prevent obesity among adults in the U.S 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,” he said.
The full study is available online here.