Body Fat Percentage as an Indicator of Adiposity in Adolescents: An Overview Based on Circadian Rhythm, Ultra-Processed Food Consumption, and Physical Activity

Obesity among adolescents is an important nutritional problem associated with an increased risk of metabolic disorders and non-communicable diseases. Body fat percentage provides a more specific assessment of adiposity than body mass index, while circadian rhythm, ultra-processed food consumption, and physical activity are lifestyle factors that may be associated with adolescent adiposity. This study aimed to analyze the characteristics of circadian rhythm, ultra-processed food consumption, physical activity, and body fat percentage and to examine the relationships of these factors with body fat percentage among adolescents. An analytical observational study with a cross-sectional design was conducted among 110 adolescents aged 16–18 years at senior high schools in Surabaya in June 2026. Circadian rhythm was assessed using the Morningness-Eveningness Questionnaire, ultra-processed food consumption was assessed using a Semi-Quantitative Food Frequency Questionnaire based on the NOVA classification, physical activity was assessed using the Physical Activity Questionnaire for Adolescents, and body fat percentage was measured using Bioelectrical Impedance Analysis. Bivariate analysis was performed using the Spearman rank correlation test with a significance level of 5%. The results show that circadian rhythm is not significantly associated with body fat percentage (r = −0.221; p = 0.053). Ultra-processed food consumption is positively and significantly associated with body fat percentage (r = 0.461; p = 0.016), whereas physical activity is negatively and significantly associated with body fat percentage (r = −0.411; p = 0.002). Thus, higher ultra-processed food consumption and lower physical activity are associated with a higher body fat percentage, whereas circadian rhythm shows no significant association with body fat percentage.