Objective: To examine associations between sociodemographic, dietary factors and physical activity and the prevalence of obesity in the Belgian general population.
Design: Base-line data from the Belgian Interuniversity Research on Nutrition and Health (BIRNH) study (1979-1984).
Subjects: A total of 5837 men and 5243 women aged 25-74y were included in the analysis. The sample was considered representative of the Belgian population.
Measurements: Using the body mass index (BMI) as the criterion, obesity was defined as a BMI> or =30 kg/m2. Nutritional data were assessed by a 24 h food record. Physical activity level (PAL) was calculated by dividing total caloric intake by an estimation of basal metabolic rate (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 women. In both sexes, prevalence of obesity increased gradually in each 10-year age category (P<0.0001) and steeply decreased with level of education. Comparing lowest (Q1) to highest quartile (Q4), after adjustment for age, prevalence of obesity decreased with total carbohydrate intake, as well as total sugar intake in both sexes, and increased with total fat intake only in men. Obesity increased with a high fat to sugar ratio (men: OR(Q4/Q1) = 1.56; confidence interval (CI): 1.25-1.93; women: OR(Q4/Q1) = 1.45; CI: 1.17-1.80). PAL was inversely and very strongly associated with obesity (men: OR(Q4/Q1) = 0.20; CI: 0.15-0.26; women: OR(Q4/Q1) = 0.18; CI: 0.14-0.23). The same 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, increased fat intake and especially elevated fat to sugar ratio appear to be powerful determinants of obesity in this Belgian population.