Comparison of Dietary Intakes Between a Large Online Cohort Study (Etude NutriNet-Sant,) and a Nationally Representative Cross-Sectional Study (Etude Nationale Nutrition Sant,) in France: Addressing the Issue of Generalizability in E-Epidemiology

Despite some advantages over traditional methods, Web-based studies elicit concerns about generalizability. To address this issue, we compared dietary intakes between an electronic (e-) cohort study and a nationally representative survey. We studied 49,443 French volunteers aged 18-74 years recruited during 2009-2010 in the NutriNet-Sant, Study, a general population-based e-cohort study. The Etude Nationale Nutrition Sant, (ENNS; 2006-2007), a cross-sectional study with a nationally representative sample of 2,754 French adults aged 18-74 years, served as the reference data set. Reported dietary intakes from three 24-hour dietary records were weighted and compared between the two studies via Student t tests for mean location, using a > 5% cutoff for establishing practically meaningful differences. We observed similar intakes as regards carbohydrates, total lipids, protein, and total energy. However, intakes of fruit and vegetables, fiber, vitamins B-6, B-9, C, D, and E, iron, and magnesium were higher in the e-cohort than in the ENNS, while intakes of alcohol and nonalcoholic beverages were lower in the e-cohort. Significant sex-specific differences were observed regarding vitamins A and B-12, zinc, and potassium. True intake differences, mode effects, and volunteer bias might each contribute to explaining the findings. In the future, repeated use of the same tool in large e-cohorts with heterogeneous dietary exposures could serve research purposes and supplement group-level monitoring of dietary trends.