This quantitative study investigated the influence of physical activity determinants and dietary habits on the Body Mass Index (BMI) of tertiary students enrolled in physical education courses in DACS‑affiliated schools in Region XI. Using data from a stratified random sample of 300 students, physical activity determinants registered a high overall mean (M = 3.74) across domains including knowledge, environmental resources, motivation, capability, skills, and self‑regulatory factors. Dietary habits showed a moderate overall mean (M = 3.24), indicating inconsistent adherence to recommended nutritional practices.

BMI classification based on Asia–Pacific cutoffs revealed that 38.2% of students fell within the normal range, while 21.9% were underweight, 15.0% were overweight, and 24.9% were obese, indicating that a majority were outside the healthy BMI category. Multiple regression analysis demonstrated that physical activity determinants significantly and negatively predicted BMI (β = −0.16, p = 0.012), whereas dietary habits significantly and positively predicted BMI (β = 0.13, p = 0.038). Together, these variables accounted for 1.8% of the variance in BMI (R² = 0.018), with the overall model reaching statistical significance (F = 3.469, p = 0.032).

These findings highlight the measurable impact of physical activity‑related factors and dietary behaviors on BMI while indicating that additional unmeasured variables may contribute substantially to weight‑related outcomes in this population.