Background: Fast food has become a prominent feature of the diet of children in the United States and, increasingly, throughout the world. However, few studies have examined the effects of fast-food consumption on any nutrition or health-related outcome. The aim of this study was to test the hypothesis that fast-food consumption adversely affects dietary factors linked to obesity risk.

Methods: This study included 6212 children and adolescents 4 to 19 years old in the United States participating in the nationally representative Continuing Survey of Food Intake by Individuals conducted from 1994 to 1996 and the Supplemental Children's Survey conducted in 1998. We examined the associations between fast-food consumption and measures of dietary quality using between-subject comparisons involving the whole cohort and within-subject comparisons involving 2080 individuals who ate fast food on one but not both survey days.

Results: On a typical day, 30.3% of the total sample reported consuming fast food. Fast-food consumption was highly prevalent in both genders, all racial/ethnic groups, and all regions of the country. Controlling for socioeconomic and demographic variables, increased fast-food consumption was independently associated with male gender, older age, higher household incomes, non-Hispanic black race/ethnicity, and residing in the South. Children who ate fast food, compared with those who did not, consumed more total energy (187 kcal; 95% confidence interval [CI]: 109-265), more energy per gram of food (0.29 kcal/g; 95% CI: 0.25-0.33), more total fat (9 g; 95% CI: 5.0-13.0), more total carbohydrate (24 g; 95% CI: 12.6-35.4), more added sugars (26 g; 95% CI: 18.2-34.6), more sugar-sweetened beverages (228 g; 95% CI: 184-272), less fiber (-1.1 g; 95% CI: -1.8 to -0.4), less milk (-65 g; 95% CI: -95 to -30), and fewer fruits and nonstarchy vegetables (-45 g; 95% CI: -58.6 to -31.4). Very similar results were observed by using within-subject analyses in which subjects served as their own controls: that is, children ate more total energy and had poorer diet quality on days with, compared with without, fast food.

Conclusion: Consumption of fast food among children in the United States seems to have an adverse effect on dietary quality in ways that plausibly could increase risk for obesity.