In the study - published in the American Journal of Clinical Nutrition - which examined the dietary intake data of 41,000 adults who took part in the CDC's National Health and Nutrition Examination Survey (NHANES) from 2001-2018, researchers calculated the percentage of calories consumed from four broad food groups:
(1) minimally processed foods or whole foods, such as vegetables, fruits, grains, meat, and dairy;
(2) processed culinary ingredients, such as olive oil, butter, sugar, and salt;
(3) processed foods, such as cheese, canned fish, and canned beans;
(4) ultra-processed foods, such as frozen pizza, soda, fast food, sweets, salty snacks, canned soup, and most breakfast cereals.
What they found is that ultra-processed foods accounted for over half (57%) of calories consumed by US adults in 2017-2018, an increase from 53.5% in the 2001-2002 period when the study began.
Recent research conducted by the Friedman School of Nutrition Science & Policy at Tufts University examining NHANES data for 33,795 children and adolescents showed a similar trend: ultra-processed foods made up 67% of child and adolescent's diet in 2018, an increase from 61.4% in 1999.
In contrast, the consumption of whole foods decreased from 32.7% to 27.4% of calories consumed, mostly due to people eating less meat and dairy, according to the study's researchers.
"The overall composition of the average US diet has shifted towards a more processed diet. This is concerning, as eating more ultra-processed foods is associated with poor diet quality and higher risk of several chronic diseases," said lead author of the study Filippa Juul, an assistant professor and postdoctoral fellow at NYU School of Public Health.
"The high and increasing consumption of ultra-processed foods in the 21st century may be a key driver of the obesity epidemic."
The trend towards increased consumption of ultra-processed foods was consistent across all demographic groups, regardless of income, except for Hispanic adults who ate significantly less ultra-processed foods than non-Hispanic white and Black adults, the research showed.
Older adults (aged 60+) had the sharpest increase in ultra-processed foods consumption and steepest decline in whole foods consumption compared to other age groups, noted researchers.
Among the types of ultra-processed foods consumed, the data revealed consumption of ready-to-heat meals like frozen dinner increased the most while the intake of sugary foods and drinks declined over the measured period.
"In the current industrial food environment, most of the foods that are marketed to us are in fact industrial formulations that are far removed from whole foods. Nevertheless, nutritional science tends to focus on the nutrient content of foods and has historically ignored the health implications of industrial food processing," added Juul.
Has the pandemic further fueled processed foods consumption?
While the data analyzed took place pre-COVID, researchers believe that the pandemic has further fueled consumption of more shelf-stable, ultra-processed foods.
"In the early days of the pandemic, people changed their purchasing behaviors to shop less frequently, and sales of ultra-processed foods such as boxed macaroni and cheese, canned soups, and snack foods increased substantially. People may have also eaten more packaged 'comfort foods' as a way of coping with the uncertainty of the pandemic," said Juul, adding that researchers will be examining NHANES from 2019-2020 once it becomes available.