Ultra-Processed Food Intake Is Associated with Dietary Quality, Dental Caries, and Constipation-Related Symptoms Among Preschool Children in Taiwan: A Cross-Sectional Study

Background/Objectives: Ultra-processed food (UPF) consumption has increased worldwide, but evidence regarding its dietary and health associations among preschool children in East Asia remains limited. This study examined the associations of UPF intake with nutrient intake, anthropometric status, dental caries, and constipation-related symptoms among preschool children in Taiwan. Methods: This cross-sectional study included 822 children aged 2–6 years recruited from 82 kindergartens in Taipei, Taiwan. Habitual dietary intake was assessed using a 107-item semi-quantitative food frequency questionnaire, and foods were classified using an adapted NOVA-based framework. Participants were categorized into quartiles according to the percentage of total energy intake derived from UPFs. Anthropometric data were available for 777 children and dental examination data for 746 children. Six constipation-related symptoms derived from the Rome IV criteria were assessed based on parental reports of symptoms during the previous 3 months. Differences across UPF quartiles were examined using chi-square tests and one-way analysis of variance. Multivariable regression models were used to evaluate associations of UPF intake and specific food groups with dental caries and constipation-related symptoms. Results: UPFs contributed a mean of 15.12% of total energy intake. Higher UPF intake was associated with lower intakes of dietary fiber, protein, potassium, calcium, magnesium, zinc, phosphorus, retinol equivalents, vitamin B1, vitamin B2, vitamin B6, vitamin B12, and vitamin C, and with higher intakes of total fat, saturated fatty acids, and sodium. No significant differences in height percentile, weight percentile, or anthropometric status were observed across UPF quartiles. Among the 746 children with dental examination data, dental caries experience (defined as the presence of at least one decayed or filled tooth) increased from 12.8% in Q1 to 31.2% in Q4 (p < 0.001). After adjustment for age group, sex, total energy intake, and frequency of home cooking, children in Q4 had a higher prevalence of dental caries than those in Q1 (aPR = 2.270, 95% CI: 1.480–3.480; p < 0.001; p for trend < 0.001). Higher UPF intake was also associated with greater constipation-related symptom scores. Compared with Q1, constipation-related symptom scores were 0.900 points higher in Q4 (β = 0.900, 95% CI: 0.330–1.470; p = 0.002). After additional adjustment for dietary fiber intake, this association was attenuated but remained significant (β = 0.680, 95% CI: 0.110–1.260; p = 0.019). In mutually adjusted food-group analyses, higher fruit intake was associated with lower constipation-related symptom scores (β = −0.219, 95% CI: −0.353 to −0.086; p = 0.001), whereas higher biscuit/snack intake was associated with higher constipation-related symptom scores (β = 1.193, 95% CI: 0.441–1.946; p = 0.002). Higher vegetable intake was associated with a lower prevalence of dental caries (aPR = 0.810, 95% CI: 0.660–0.990; p = 0.038). Conclusions: Higher UPF intake among Taiwanese preschool children was associated with an unfavorable nutrient profile, higher dental caries prevalence, and more frequent constipation-related symptoms, but not with differences in anthropometric status. The attenuation of the UPF–constipation association after adjustment for dietary fiber suggests that lower fiber intake may partly contribute to this association. These findings support dietary guidance that emphasizes reducing UPF consumption and promoting minimally processed, nutrient-dense foods, particularly fruits, vegetables, and other fiber-rich foods, during early childhood.