Trends in Consumption of Ultraprocessed Foods Among US Youths Aged 2-19 Years, 1999-2018

Key Points

Question  What were the trends in consumption of ultraprocessed foods among US youths from 1999 to 2018?

Findings  In this serial cross-sectional study of nationally representative data from 33 795 US youths aged 2-19 years, the estimated percentage of total energy consumed from ultraprocessed foods increased from 61.4% to 67.0%, whereas the percentage of total energy consumed from unprocessed or minimally processed foods decreased from 28.8% to 23.5%.

Meaning  From 1999 to 2018, the estimated proportion of energy intake from consumption of ultraprocessed foods increased in the US among youths and comprised the majority of their total energy intake.

Importance  The childhood obesity rate has been steadily rising among US youths during the past 2 decades. Increasing evidence links consumption of ultraprocessed foods to excessive calorie consumption and weight gain, but trends in the consumption of ultraprocessed foods among US youths have not been well characterized.

Objective  To characterize trends in the consumption of ultraprocessed foods among US youths.

Design, Setting, and Participants  Serial cross-sectional analysis using 24-hour dietary recall data from a nationally representative sample of US youths aged 2-19 years (n = 33 795) from 10 cycles of the National Health and Nutrition Examination Survey (NHANES) from 1999-2000 to 2017-2018.

Exposures  Secular time.

Main Outcomes and Measures  Percentage of total energy consumed from ultraprocessed foods as defined by NOVA, an established food classification system that categorizes food according to the degree of food processing.

Results  Dietary intake from youths were analyzed (weighted mean age, 10.7 years; 49.1% were girls). From 1999 to 2018, the estimated percentage of total energy from consumption of ultraprocessed foods increased from 61.4% to 67.0% (difference, 5.6% [95% CI, 3.5% to 7.7%]; P < .001 for trend), whereas the percentage of total energy from consumption of unprocessed or minimally processed foods decreased from 28.8% to 23.5% (difference, −5.3% [95% CI, −7.5% to −3.2%]; P < .001 for trend). Among the subgroups of ultraprocessed foods, the estimated percentage of energy from consumption of ready-to-heat and -eat mixed dishes increased from 2.2% to 11.2% (difference, 8.9% [95% CI, 7.7% to 10.2%]) and from consumption of sweet snacks and sweets increased from 10.7% to 12.9% (difference, 2.3% [95% CI, 1.0% to 3.6%]), but the estimated percentage of energy decreased for sugar-sweetened beverages from 10.8% to 5.3% (difference, −5.5% [95% CI, −6.5% to −4.5%]) and for processed fats and oils, condiments, and sauces from 7.1% to 4.0% (difference, −3.1% [95% CI, −3.7% to −2.6%]) (all P < .05 for trend). There was a significantly larger increase in the estimated percentage of energy from consumption of ultraprocessed foods among non-Hispanic Black youths (from 62.2% to 72.5%; difference, 10.3% [95% CI, 6.8% to 13.8%]) and Mexican American youths (from 55.8% to 63.5%; difference, 7.6% [95% CI, 4.4% to 10.9%]) than the increase among non-Hispanic White youths (from 63.4% to 68.6%; difference, 5.2% [95% CI, 2.1% to 8.3%]) (P = .04 for trends).

Conclusions and Relevance  Based on the NHANES cycles from 1999 to 2018, the estimated proportion of energy intake from consumption of ultraprocessed foods has increased among youths in the US and has consistently comprised the majority of their total energy intake.

Quiz Ref IDUltraprocessed foods are ready-to-eat or ready-to-heat industrial formulations made mainly with ingredients refined or extracted from foods and contain additives but little to no whole foods.¹ Although the processing of foods plays a critical role in improving food security and ensuring food safety,² ultraprocessed foods are typically high in added sugar, trans-fat, sodium, and refined starch and low in fiber, protein, vitamins, and minerals.³Quiz Ref ID Cohort studies provide consistent evidence suggesting that high intake of ultraprocessed foods contributes to obesity and cardiometabolic risk factors in children and adults,^4-8 and is associated with an increased risk of cardiovascular diseases,^9,10 certain types of cancers,¹¹ and total mortality in adults.^12,13

The childhood obesity rate has been steadily rising among US youths during the past 2 decades.^14,15 However, the temporal trends in the consumption of ultraprocessed foods among US youths are not well established. Furthermore, potential differences among population subgroups and trends in major subgroups of ultraprocessed foods have not been evaluated. This study characterized trends in the consumption of ultraprocessed foods among US youths aged 2-19 years from 1999 to 2018 (overall and among population subgroups) using data from 10 consecutive cycles of the National Health and Nutrition Examination Survey (NHANES). This study further assessed major subgroups of ultraprocessed foods consumed by US youths in the latest cycle of NHANES (2017-2018) and the associated nutrient profiles. Such information can inform priorities and policies around the consumption of ultraprocessed foods and improve the diet quality of US youths.

NHANES is a series of cross-sectional surveys that assesses the health and nutritional status of the US noninstitutionalized civilian population in the 50 states and the District of Columbia. Details on the study design, protocol, and data collection methods are documented elsewhere.¹⁶ The NHANES protocols were approved by the National Center for Health Statistics research ethics review board. Written parental informed consent was obtained for all youths aged 2-17 years. In addition to parental consent, child and adolescent assent was obtained from all youths aged 7-17 years. Written informed consent was obtained from young adults aged 18-19 years.

This study used dietary data collected via 24-hour dietary recalls conducted by trained interviewers among US youths aged 2-19 years between 1999-2000 and 2017-2018. Participants aged 12-19 years completed the dietary recall interview on their own and proxy-assisted interviews were conducted for participants aged 6-11 years. For participants aged 5 years or younger, a proxy who was familiar with the dietary intake of the child responded to the dietary interview. The US Department of Agriculture (USDA) Automated Multiple-Pass Method was used to enhance complete and accurate recall of all foods and beverages consumed during the previous day and reduce respondent burden across all NHANES cycles. From 1999 to 2002, one recall was conducted in person at the mobile examination center; from 2003 to 2018, a second recall, administered over the phone, was added approximately 3 to 10 days after the first recall. Dietary data from the first recall were included in the present analysis. The overall examination response rate among youths at the mobile examination center ranged from 49% to 80% during the study period; 91% provided a valid dietary recall on the first day. The 39 participants who did not provide a valid recall were excluded.

Foods and beverages consumed during each NHANES cycle were classified into 4 major groups (unprocessed or minimally processed foods [group 1], processed culinary ingredients [group 2], processed foods [group 3], and ultraprocessed foods [group 4]) based on the extent and purpose of industrial processing according to the NOVA classification system. The NOVA classification system defined ultraprocessed foods as formulations of ingredients, mostly of exclusive industrial use, resulting from a series of industrial processes (eMethods 1 and eTable 1 in the Supplement).^1,17 Ingredients that are characteristic of ultraprocessed foods include substances of no or rare culinary use (eg, high-fructose corn syrup, hydrogenated oils) and additives to make the final product palatable (eg, flavor enhancers, colors, emulsifiers). Examples of ultraprocessed foods include sweet or savory packaged snacks, sugar-sweetened beverages, candy, industrial bread, industrial breakfast cereal, ready-to-heat and -eat pasta dishes and pizza, and sausages and other reconstituted meat products.

To assign a food or beverage into 1 of the 4 NOVA groups, the food description and ingredient list were assessed for each NHANES food code using the cycle-specific USDA Food and Nutrition Database for Dietary Studies and the USDA National Nutrient Database for Standard Reference.^18,19 For foods with a handmade recipe, the classification was applied to the underlying ingredients to improve accuracy. The energy and nutrient contents of each NOVA food group and subgroup were further estimated using the cycle-specific USDA Food and Nutrition Database for Dietary Studies, the USDA National Nutrient Database for Standard Reference, and the USDA Food Patterns Equivalents Database (eg, for added sugar).

The percentage of energy consumed from each NOVA food group and subgroup was computed as the population ratio of the mean energy from that food group over the mean total energy intake.²⁰ The primary outcome was the percentage of total energy consumed from ultraprocessed foods. The percentage of total energy consumed from the other NOVA food groups was reported for context. The secondary outcomes included the percentage of energy intake from ultraprocessed foods among population subgroups, the percentage of energy intake from subgroups of ultraprocessed foods, and the nutrient profiles of major ultraprocessed foods consumed by US youths, including the percentage of calories from macronutrients and the mean intake levels of micronutrients per 100 kcal of ultraprocessed foods.

Trends in consumption of ultraprocessed foods were further assessed among population subgroups by age (2-5, 6-11, and 12-19 years), sex (boys and girls), race/ethnicity (non-Hispanic White, non-Hispanic Black, and Mexican American), parental education level for the head of the household (<high school; high school graduate, general equivalency diploma, or some college; and college graduate), and family income to federal poverty ratio (<1.30, 1.30-2.99, and ≥3.00). We evaluated trends in consumption of ultraprocessed foods by race/ethnicity because prior research documented differences in dietary intake patterns by race/ethnicity among US youths.²¹ Participants (or a household proxy for participants aged <16 years) reported information on race/ethnicity according to fixed categories. Trends for Asian/Pacific Islander youths and other Hispanic youths were not analyzed because reliable estimates for these groups were not available across all NHANES cycles.²²

The percentage of energy intake was chosen as the unit of measure in this analysis to adjust for total energy intake, thus reducing measurement errors and extraneous variations in dietary intake such as those due to metabolic rate or physical activity.²³ To ensure nationally representative estimates, all analyses incorporated the appropriate sampling weights to account for the complex sampling design, nonresponses, and allocations by weekdays for the day 1 dietary recall. The significance of linear trends was examined by including the NHANES 2-year cycle as a continuous variable in the survey-weighted linear regression models.

Nonlinearity for the trends was tested by including a quadratic term of survey cycle in the model.²⁴ Model assumption was further evaluated by inspecting the diagnostic plots (eMethods 2 in the Supplement). Because nonlinear trends were not detected, all analyses presented are based on linear regression models with a linear time term (ie, survey cycle). Change in consumption was calculated as the absolute difference in percentage of energy from the earliest NHANES cycle (1999-2000) to the latest NHANES cycle (2017-2018). To determine the degree to which observed trends were driven by demographic changes, sensitivity analyses were performed with adjustments for sociodemographic characteristics. Consumption for each NOVA food group was further evaluated by food source and eating location.

To examine potential differences in trends of consumption of ultraprocessed foods by population subgroups, the Wald F test was used to evaluate an interaction term between the 2-year survey cycle and each demographic factor. Nutrient profiles of ultraprocessed foods were assessed using data collected in 2017-2018 and compared with those of foods not ultraprocessed (ie, a combination of unprocessed or minimally processed foods, processed culinary ingredients, and processed foods) using t tests. The mean levels of nutrient consumption by US youths across quintiles of consumption of ultraprocessed foods were further compared using linear regression models. Because no adjustments were made for multiple comparisons, the findings for the secondary outcomes should be interpreted as exploratory.

All data were analyzed using SAS version 9.4 (SAS Institute Inc) and statistical significance was set at a 2-tailed P < .05 for all analyses.

A total of 33 795 youths aged 2-19 years (weighted mean age, 10.7 years; n = 16 775 [49.1%] were girls) were included in this analysis. From 1999-2000 to 2017-2018, the proportion of non-Hispanic White youths decreased from 58.6% to 52.3%, whereas the proportion of Mexican American youths increased from 11.2% to 16.5% (Table 1). The proportion of youths with parental (head of household) education level of college graduate increased from 22.1% to 27.7%.

From 1999-2000 to 2017-2018, the estimated percentage of total energy from consumption of ultraprocessed foods (NOVA group 4) significantly increased from 61.4% to 67.0% (difference, 5.6% [95% CI, 3.5% to 7.7%]; P < .001 for trend), whereas the percentage of total energy from consumption of unprocessed or minimally processed foods (NOVA group 1) significantly decreased from 28.8% to 23.5% (difference, −5.3% [95% CI, −7.5% to −3.2%]; P < .001 for trend) (Table 2 and eTable 2 in the Supplement). The estimated percentage of energy from consumption of processed culinary ingredients (NOVA group 2) also significantly increased from 2.4% to 3.4% (difference, 1.0% [95% CI, 0.6% to 1.4%]; P = .03 for trend) but did not significantly change for processed foods (NOVA group 3) (from 6.1% to 6.0%; difference, −0.03% [95% CI, −0.7% to 0.6%]; P = .44 for trend). Adjusting for changes in sociodemographic characteristics did not alter the results (eTable 3 in the Supplement).

From 1999-2000 to 2017-2018, the estimated percentage of energy from consumption of ready-to-heat and -eat mixed dishes significantly increased from 2.2% to 11.1% (difference, 8.9% [95% CI, 7.7% to 10.2%]; P < .001 for trend) and significantly increased for sweet snacks and sweets from 10.6% to 12.9% (difference, 2.3% [95% CI, 1.0% to 3.6%]; P = .02 for trend) (Table 2). The estimated percentage of energy from consumption of sugar-sweetened beverages significantly decreased from 10.8% to 5.3% (difference, −5.5% [95% CI, −6.5% to −4.5%]) and significantly decreased for processed fats or oils, condiments, and sauces from 7.1% to 4.0% (difference, −3.1% [95% CI, −3.7% to −2.6%]) (P < .001 for trend for both comparisons). In 2017-2018, the subgroups of ultraprocessed foods that contributed to the largest estimated percentage of energy were industrial grain foods (14.5%), followed by sweet snacks and sweets (12.9%) and ready-to-heat and -eat mixed dishes (11.1%).

Among the ready-to-heat and -eat mixed dishes subgroup (Figure 1 and eTable 4 in the Supplement), the estimated percentage of energy significantly increased for all major subcategories including pizza (difference, 5.1% [95% CI, 4.5% to 5.8%]), sandwiches or hamburgers (difference, 1.5% [95% CI, 1.1% to 1.8%]), and other (difference, 2.3% [95% CI, 1.6% to 3.1%]). Among the sweet snacks and sweets subgroup, the estimated percentage of energy increased significantly for sweet bakery products (difference, 2.3% [95% CI, 1.4% to 3.2%]) and cereal and nutrition bars (difference, 0.4% [95% CI, 0.2% to 0.7%]). Among sugar-sweetened beverages subgroup, the estimated percentage of energy decreased significantly for both soft drinks (difference, −4.3% [95% CI, −5.1% to −3.4%]) and fruit and other sweetened drinks (difference, −1.2% [95% CI, −1.7% to −0.8%]) (all P < .05 for trend).

Similar proportions of ultraprocessed foods were eaten at school cafeterias (6.6% vs 6.3%; P = .85 for difference). In addition, ultraprocessed foods were more likely to be consumed away from home compared with unprocessed or minimally processed foods (34.3% vs 24.6%) and at fast-food restaurants (18.6% vs 6.0%) (both P < .001 for difference; eFigure in the Supplement).

The significantly increasing trend in the estimated percentage of energy from consumption of ultraprocessed foods was observed among all population subgroups from 1999-2000 to 2017-2018; however, the increase was significantly higher among non-Hispanic Black youths (from 62.2% to 72.5%; difference, 10.3% [95% CI, 6.8%-13.8%]) and Mexican American youths (from 55.8% to 63.5%; difference, 7.6% [95% CI, 4.4%-10.9%]) than the increase among non-Hispanic White youths (from 63.4% to 68.6%; difference, 5.2% [95% CI, 2.1%-8.3%]) (P = .04 for trends; Figure 2 and eTable 5 in the Supplement). In 2017-2018, youths aged 6-11 years (69.0%) and aged 12-19 years (67.7%) consumed a significantly higher percentage of energy from ultraprocessed foods than those aged 2-5 years (61.1%) (P < .001 for difference). Participants with missing data on parental education level (n = 1309; <5%) and family income to poverty ratio (n = 2527; 10%) were excluded from the corresponding subgroup analyses.

At the food level, the ultraprocessed foods consumed by US youths in 2017-2018 contained a statistically significantly higher estimated percentage of calories from carbohydrates compared with the foods not ultraprocessed (55.2% vs 43.4%) and added sugars (19.3% vs 3.4%), but a lower level of fiber (0.67 g/100 kcal vs 0.87 g/100 kcal) and percentage of calories from protein (10.5% vs 20.6%). Ultraprocessed foods also contained statistically significantly higher levels of sodium, iron, vitamin E, and folic acid but lower levels of other vitamins and minerals than foods not ultraprocessed (Table 3 and eTable 6 in the Supplement). At the population level, youths in the higher quintile of percentage of energy from ultraprocessed foods consumed statistically significantly higher levels of carbohydrates, total fats, polyunsaturated fats, and added sugars but lower levels of protein, fiber, calcium, magnesium, potassium, zinc, vitamins A, C, and D, and folate (eTable 7 in the Supplement).

Quiz Ref IDIn this analysis of nationally representative data, US youths consumed a majority of their daily calories from ultraprocessed foods. The estimated percentage of energy consumed from ultraprocessed foods increased from 1999 to 2018, with an increasing trend in ready-to-heat and -eat mixed dishes and a decreasing trend in sugar-sweetened beverages. Non-Hispanic Black youths and Mexican American youths had a greater increase in the percentage of energy from consumption of ultraprocessed foods than non-Hispanic White youths.

The overall increase in the estimated percentage of energy from ultraprocessed foods was mainly contributed by increases in the consumption of ready-to-heat and -eat mixed dishes. This finding is in accordance with a prior study that reported increases in purchases of ready-to-heat and -eat mixed dishes by US households from 2000 to 2012 (164-189 kcal/d per person).²⁵ Reasons for such an increase are unknown and may include the increased availability and portion size of ready-to-heat and -eat meals in the US market²⁶ and the increased consumption of food prepared away from home during the past few decades.²⁷

Consumption of sugar-sweetened beverages decreased among US youths during the past 20 years. Such a decline may reflect increased policy efforts during recent decades to reduce consumption of sugar-sweetened beverages and concurrent awareness of the adverse effects of consumption of sugar-sweetened beverages on the health of youths.^28,29 However, in this study there was an increase in the consumption of sweet bakery products and sweet snacks. Sweet bakery products (such as cakes and pies, cookies and brownies, and doughnuts) and sweet snacks (such as candy and ice cream) are the second most commonly consumed source of added sugars among US youths (accounting for approximately 21%-31% of total added sugars consumed by US youths).³⁰ Public health efforts are needed to reduce the number of sugars being added to sweet bakery products and sweet snacks during food processing.³¹

Quiz Ref IDThis study observed a greater increase in the consumption of ultraprocessed foods among non-Hispanic Black youths than non-Hispanic White youths. Targeted marketing of junk foods toward racial/ethnic minority youths may partly contribute to such differences.^32,33 However, persistently lower consumption of ultraprocessed foods among Mexican American youths may reflect more home cooking among Hispanic families.³⁴ A higher consumption of ultraprocessed foods among school-aged youths than preschool children (aged 2-5 years) may reflect increased marketing, availability, and selection of ultraprocessed foods for older youths.²¹ The lack of disparities by parental education level and family income to poverty ratio suggests that ultraprocessed foods are pervasive in the diet of US youths and supports the need to reduce consumption of ultraprocessed foods among all population subgroups.

Quiz Ref IDUltraprocessed foods consumed by US youths had an overall poorer nutrient profile than foods not ultraprocessed. However, ultraprocessed foods had lower levels of saturated fat than foods not ultraprocessed. Ultraprocessed foods contained more carbohydrates than foods not ultraprocessed, most of which were from low-quality carbohydrates reflected by a high percentage of calories from added sugars and low levels of dietary fiber and protein. Despite a higher total folate content in ultraprocessed foods, which reflects a higher level of folic acid fortification, youths who consumed a higher level of ultraprocessed foods had lower consumption of total folate due to lower consumption of folate from whole foods. In addition to poor nutrient profiles, processing itself may convey adverse health effects by changing the physical structure and chemical composition of food, which could elicit elevated glycemic response and reduced satiety.^35,36

Furthermore, food additives in ultraprocessed foods such as emulsifiers, stabilizers, and artificial sweeteners have been linked to adverse metabolic effects in animal studies.³⁷ A 2019 randomized clinical trial in 20 adults demonstrated that diets derived mostly from eating ultraprocessed foods, compared with eating unprocessed foods, led to 508 kcal/d higher energy intake ad libitum despite the fact that the 2 diets were matched for calories, sugar, fat, sodium, fiber, and macronutrients.³⁸ These results suggest that food processing may need to be considered as a food dimension in addition to nutrients and food groups in future dietary recommendations and food policies.

A strength of this study is the use of 20 years of nationally representative dietary data collected using standard procedures and providing generalizability to US youths. The 24-hour dietary recall provides more accurate estimation of consumption than other methods such as food frequency questionnaires, particularly with respect to energy intake and processing of foods.²⁵

This study has several limitations. First, self-reported dietary recalls are subject to measurement error. Second, even though social desirability bias leading to underestimation may differ among population subgroups, the sensitivity analysis that adjusted for age, sex, and race/ethnicity confirmed the main findings.

Third, updates of food codes in each NHANES cycle could have influenced observed trends¹⁸ and may have partly contributed to a higher increase in the estimated consumption of ultraprocessed foods between certain NHANES cycles than others. However, it is unlikely that these updates had a substantial influence on the overall increasing trend from 1999-2018. Fourth, data for food processing in NHANES (product brand and ingredient list) are still limited, which may lead to misclassification.

Fifth, the NOVA classification system has been criticized by others for its simplistic definition and limited policy implications.³⁹ For example, NOVA does not consider some added food chemicals (such as pesticide residuals) or contaminants (such as perfluoroalkyl and polyfluoroalkyl substances) that can also lead to adverse health outcomes. In addition, NOVA classifies foods based on the nature, extent, and purpose of industrial food processing as opposed to nutrient profiles and poses a challenge to the well-accepted food classifications used by dietary recommendations, which are predominantly nutrient based. However, NOVA is reproducible and is the most commonly used classification and adds a new dimension to food classification that is overlooked.⁴⁰ The accumulating evidence linking consumption of ultraprocessed foods classified by NOVA and health outcomes supports its application in epidemiological and policy research.^4-13

Based on the NHANES cycles from 1999 to 2018, the estimated proportion of energy intake from consumption of ultraprocessed foods has increased among youths in the US and has consistently comprised the majority of their total energy intake.

Corresponding Author: Fang Fang Zhang, MD, PhD, Friedman School of Nutrition Science and Policy, Tufts University, 150 Harrison Ave, Boston, MA 02111 (fang_fang.zhang@tufts.edu).

Accepted for Publication: June 6, 2021.

Author Contributions: Drs Wang and F. F. Zhang had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: Wang, Herrick, Mozaffarian, F. F. Zhang.

Acquisition, analysis, or interpretation of data: All authors.

Drafting of the manuscript: Wang, Du, Pomeranz.

Critical revision of the manuscript for important intellectual content: Wang, Martínez Steele, Pomeranz, O’Connor, Herrick, Luo, X. Zhang, Mozaffarian, F. F. Zhang.

Statistical analysis: Wang, Du, O’Connor, Luo, X. Zhang.

Obtained funding: Mozaffarian, F. F. Zhang.

Administrative, technical, or material support: X. Zhang, F. F. Zhang.

Supervision: Herrick, Mozaffarian, F. F. Zhang.

Conflict of Interest Disclosures: Dr Mozaffarian reported receiving research funding from the Bill & Melinda Gates Foundation, the National Institutes of Health, and the Rockefeller Foundation; receiving personal fees from Acasti Pharma, Amarin, America’s Test Kitchen, Barilla, Cleveland Clinic Foundation, Danone, GOED, and Motif FoodWorks; serving on scientific advisory boards for Beren Therapeutics, Brightseed, Calibrate, DayTwo (ended in June 2020), Elysium Health, Filtricine, Foodome, HumanCo, January Inc, Perfect Day, Season, and Tiny Organics; and receiving chapter royalties from UpToDate; all outside the submitted work. No other disclosures were reported.

Funding/Support: This study was supported by grant R01MD011501 from the National Institutes of Health (awarded to Dr F. F. Zhang) and Processo grant 2018/17972-9 from the São Paulo Research Foundation (awarded to Dr Martínez Steele).

Role of the Funder/Sponsor: The National Institutes of Health and the São Paulo Research Foundation had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.