Trends in BMI among Belgian children, adolescents and adults from 1969 to 1996

OBJECTIVE: To document secular data on changes in the distribution of body mass index (BMI), to determine the probability of overweight at 40 y of age in Belgian males in relation to the presence or absence of overweight at different ages in adolescence, and to estimate tracking of BMI in Belgian males in Belgium aged 12-40 y. DESIGN: Cross-sectional and mixed longitudinal surveys in nationally representative samples of Belgian males and females. SUBJECTS: Cross-sectional - more than 21 000 boys and 9698 girls; to examine secular trends - 3164 boys and 5140 girls; to examine tracking - 161 males. MEASURES: Body mass and height to determine BMI. RESULTS: In Belgian children the degree of overweight has increased between 1969 and 1993. Tracking of BMI is high in adolescence (r = 0.77) and adulthood (r = 0.69-0.91) and moderate from adolescence to adulthood (r = 0.49). In Belgian males, the probability of overweight at 40 y of age in the presence of overweight at different ages in adolescence is important (odds ratios 5.0-6.9). CONCLUSIONS: Cross-sectional and longitudinal data, trends and tracking of BMI from 1969 until 1996 in Belgium indicate an increase in the degree of childhood overweight and obesity. Moreover, the risk of an overweight male adolescent becoming an overweight adult is substantial. Measures to restrict the Belgian overweight and obesity epidemic should be taken.