BACKGROUND/OBJECTIVES: Healthy diet, regular physical activity (PA), and minimizing sedentary behavior (SB) are crucial in promoting adolescents' health and well-being. We assessed adherence to PA and SB recommendations among a representative sample of adolescents and explored their relationship with diet and diet-related behaviors. METHODS: Data from the Greek arm of the 2017/2018 international Health Behavior in School-Aged Children (HBSC) cross-sectional study were used, including a probability sample of 3357 students (47.6% boys) who were 11, 13, and 15 years old. PA, SB, consumption of food groups/beverages, and diet-related behaviors were self-reported. Multiple logistic regression was used to identify potential associations. RESULTS: Most students failed to meet PA (83.9%) (i.e., ≥1 h of moderate-to-vigorous physical activity/day) and SB (90.2%) (i.e., ≤2 h of screen time/day) recommendations. Daily consumption of fruit and vegetables compared to consumption at ≤1 day/week was associated with increased adherence to PA recommendations (adjusted Odds Ratio (aOR) = 2.26, 95% Confidence Intervals (CI): 1.62-3.17 for fruit
aOR = 1.35, 95%CI: 1.00-1.82 for vegetables). Eating sweets ≤1 day/week vs. every day was associated with higher adherence to SB recommendations (aOR = 2.41, 95%CI: 1.43-4.04). Poor diet quality was related to lower adherence to PA and SB recommendations. Daily breakfast consumption vs. never and abstaining from eating at fast-food restaurants were associated with better adherence to PA and SB recommendations. Rarely eating in front of screens was associated with substantially higher odds of adhering to SB recommendations (aOR = 5.79, 95%CI: 3.67-9.14). CONCLUSIONS: Healthier diet/diet-related behaviors were associated with increased PA and reduced SB in this sample of adolescents.