Objective: To study the association between self-reported leisure time physical activity at baseline (1984-1986) and change in body mass index (BMI) during an 11-year follow-up period (1995-1997). The study population was 9357 healthy women, aged 20-49 years, who had a normal body weight (BMI 18.5-24.9 kg/m2) at baseline.
Methods: A general population-based health survey was performed both in 1984-1986 (HUNT 1) and 1995-1997 (HUNT 2). Leisure time physical activity at HUNT 1 was categorized into high, moderate, and low levels based on self-reported intensity, duration, and frequency. Women who at baseline reported diabetes, stroke, angina, myocardial infarction, or long-term illnesses impairing their activities of living were excluded.
Results: Physical activity was a significant predictor of BMI at HUNT 2 adjusted for BMI,age, and education at HUNT 1. Low level of leisure time physical activity compared with high level at baseline was significantly associated with a higher BMI 11 years later. Those with high level of activity gained 0.18 kg/m2 (95% CI 0.05, 0.32) less than those with low level of physical activity over 11 years.
Conclusions: This study has demonstrated that leisure time physical activity has a moderate effect on BMI. However, not even a high level of leisure time physical activity was sufficient to prevent weight gain and BMI increase in all subgroups of the study population.