Survey year 1995-6 1998-9 2005-6 Educational level (%) Primary Secondary University Age group (%) 18-24 25-34 35-44 45-54 55-64 65-74 75+ Period Men [18- 34] [35- 44] [45- 54] [55- 64] [65- 74] [75+ Women [18- 34] [35- 44] [45- 54] [55- 64] [65- 74] [75+] 6.0 13.9 19.5 20.1 17.7 12.9 5.5 13.5 20.5 22.8 22.6 16.6 Obesity defined as a BMI ≥30 kg/m2. Data for Switzerland obtained from [10]; data from France obtained from [39]. a: for age group 25-34 years. Results are expressed in percentage. Men 1 (ref.) 1.14 [1.09 - 1.19] 1.20 [1.14 - 1.26] 1.45 [1.34 - 1.56] 1.26 [1.16 - 1.36] 1 (ref.) 1 (ref.) 2.55 [2.36 - 2.76] 4.05 [3.74 - 4.37] 5.11 [4.72 - 5.54] 4.99 [4.59 - 5.42] 4.19 [3.85 - 4.56] 2.98 [2.71 - 3.27] Women 1 (ref.) 1.07 [1.03 - 1.12] 1.20 [1.14 - 1.26] 3.12 [2.86 - 3.40] 1.59 [1.45 - 1.74] 1 (ref.) 1 (ref.) 2.21 [1.99 - 2.44] 3.64 [3.31 - 4.01] 5.20 [4.72 - 5.74] 5.59 [5.06 - 6.17] 4.87 [4.40 - 5.38] 2.83 [2.55 - 3.15] 4.9 7.8 10.3 13.4 13.3 9.2 4.6 6.0 8.7 10.8 13.1 9.9 7.5 a 11.5 15.0 19.0 17.0 10.0 a 15.0 15.0 18.0 16.0 8.5 a 13.0 16.0 20.0 18.0 12.0 a 14.5 16.0 19.5 18.0 Marques-Vidal et al. BMC Public Health 2011, 11:772 http://www.biomedcentral.com/1471-2458/11/772 Table 5 Multivariate analysis of the determinants of overweight in the Portuguese population, by gender Statistical analysis by logistic regression after excluding subjects with obesity. Results are expressed as Odds-ratio and [95% confidence interval]. The results for each variable are adjusted for the other two. Obesity was defined as a body mass index ≥25 and <30 kg/m2. Table 6 Prevalence of uncorrected, reported obesity in Switzerland and other countries, by age group Portugal 2005-6 Switzerland, 2007 France, 2006 France, 2009 Page 7 of 8 time, given that the prevalence of obesity is also increas- ing, and this has an impact on the observed trend. The changes in educational level can also lead to selective bias, but its magnitude is difficult to assess, as it has been suggested that lesser educated people overestimate their height while better educated people underestimate their weight [37]. Hence, it is likely that the real trend is actually worse than observed, although the opposite has been suggested. Further, for the 2005-6 raw, unweighted data was used, which might not correspond exactly to the weight of each region. Still, the unweighted esti- mates for obesity (15.1%, 14.1% and 16.0% for overall, men and women, respectively) were quite similar to the weighted ones (15.2%, 14.3% and 16.0% for overall, men and women, respectively [17]). Hence, it does not appear that using unweighted data from the 2005-6 led to con- siderable differences in obesity prevalence estimates. Finally, as participation rates differed between regions, it is possible that the exact prevalence of overweight and obesity might be slightly different from the reported in this study. Still, as we could find no data regarding the regional participation rates of the previous studies, it is currently not possible to know if these participation rates changed during time and what might be their impact on the estimations provided. Nevertheless, it should be noted that these household participation rates were comparable to another study (75%) [38]. Conclusion Between 1995 and 2005, obesity increased while over- weight remained stable in the adult Portuguese popula- tion. Taking into account underestimation due to self- reporting, more than half of the Portuguese population is currently overweight or obese. Although higher rates were found among lesser educated subjects, the strong increase in BMI and obesity levels in highly educated subjects is of concern. Acknowledgements We would like to thank Drs. Carlos Matias Dias and Baltazar Nunes from the Portuguese National Institute of Health (http://www.insa.pt) for the information provided. Funding: none. Author details 1Institute of Social and Preventive Medicine (IUMSP), CHUV and Faculty of biology and medicine, Lausanne, Switzerland. 2Unidade de Nutrição e Metabolismo, Instituto de Medicina Molecular da Faculdade de Medicina da Universidade de Lisboa, Portugal. Authors’ contributions PMV designed the study, ran the statistical analysis and wrote part of the manuscript. PR obtained the data and wrote part of the manuscript. FP revised the manuscript critically for important intellectual content. All authors (PMV; PR and FP) have given final approval of the version to be published. Declaration of competing interests The authors report no competing interests.