OBJECTIVE: To examine associations between sociodemographic, dietary factor
s and physical activity and the prevalence of obesity in the Belgian genera
DESIGN: Base-line data from the Belgian Interuniversity Research on Nutriti
on and Health (BIRNH) study (1979-1984).
SUBJECTS: A total of 5837 men and 5243 women aged 25-74y were included in t
he analysis. The sample was considered representative of the Belgian popula
MEASUREMENTS: Using the body mass index (BMI) as the criterion, obesity was
defined as a BMI greater than or equal to 30 kg/m(2). Nutritional data wer
e assessed by a 24 h food record. Physical activity level (PAL) was calcula
ted by dividing total caloric intake by an estimation of basal metabolic ra
te (BMR, predicted from gender, weight and age). Age-adjusted odds ratios (
OR) of the prevalence of obesity were estimated by multilogistic regression
analysis. RESULTS: Prevalence of obesity was 12.1% in men and 18.4% in wom
en. In both sexes, prevalence of obesity increased gradually in each 10-yea
r age category (P < 0.0001) and steeply decreased with level of education.
Comparing lowest (Q1) to highest quartile (Q4), after adjustment for age, p
revalence of obesity decreased with total carbohydrate intake, as well as t
otal sugar intake in both sexes, and increased with total fat intake only i
n men. Obesity increased with a high fat to sugar ratio (men: ORQ4/Q1 = 1.5
6; confidence interval (CI): 1.25-1.93; women: ORQ4/Q1 = 1.45; CI: 1.17-1.8
0). PAL was inversely and very strongly associated with obesity (men: ORQ4/
Q1 = 0.20; CI: 0.15 - 0.26; women: ORQ4/Q1 = 0.18; CI: 0.14 - 0.23). The sa
me associations were observed with the mean BMI.
CONCLUSION: This study indicates that prevalence of obesity is particularly
high in Belgium. Low level of education and reduced physical activity, inc
reased fat intake and especially elevated fat to sugar ratio appear to be p
owerful determinants of obesity in this Belgian population.