BackgroundNutrition-related chronic diseases such as cardiovascular diseases and cancer are of multiple origin, and may be due to genetic, biologic, behavioural and environmental factors. In order to detangle the specific role of nutritional factors, very large population sample cohort studies comprising precisely measured dietary intake and all necessary information for accurately assessing potential confounding factors are needed. Widespread use of internet is an opportunity to gradually collect huge amounts of data from a large sample of volunteers that can be automatically verified and processed. The objectives of the NutriNet-Santé study are: 1) to investigate the relationship between nutrition (nutrients, foods, dietary patterns, physical activity), mortality and health outcomes; and 2) to examine the determinants of dietary patterns and nutritional status (sociological, economic, cultural, biological, cognitive, perceptions, preferences, etc.), using a web-based approach.Methods/designOur web-based prospective cohort study is being conducted for a scheduled follow-up of 10 years. Using a dedicated web site, recruitment will be carried out for 5 years so as to register 500 000 volunteers aged ≥ 18 years among whom 60% are expected to be included (having complete baseline data) and followed-up for at least 5 years for 240 000 participants. Questionnaires administered via internet at baseline and each year thereafter will assess socio-demographic and lifestyle characteristics, anthropometry, health status, physical activity and diet. Surveillance of health events will be implemented via questionnaires on hospitalisation and use of medication, and linkage with a national database on vital statistics. Biochemical samples and clinical examination will be collected in a subsample of volunteers.DiscussionSelf-administered data collection using internet as a complement to collection of biological data will enable identifying nutrition-related risks and protective factors, thereby more clearly elucidating determinants of nutritional status and their interactions. These are necessary steps for further refining nutritional recommendations aimed at improving the health status of populations.

Online self-administered data collection, by reducing the logistic burden and cost, could advantageously replace classical methods based on dietitian's interviews when assessing dietary intake in large epidemiological studies. Studies comparing such new instruments with traditional methods are necessary. Our objective was to compare one NutriNet-Santé web-based self-administered 24 h dietary record with one 24 h recall carried out by a dietitian. Subjects completed the web-based record, which was followed the next day by a dietitianconducted 24 h recall by telephone (corresponding to the same day and using the same computerised interface for data entry). The subjects were 147 volunteers aged 48 -75 years (women 59·2 %). The study was conducted in February 2009 in France. Agreement was assessed by intraclass correlation coefficients (ICC) for foods and energy-adjusted Pearson's correlations for nutrients. Agreement between the two methods was high, although it may have been overestimated because the two assessments were consecutive to one another. Among consumers only, the median of ICC for foods was 0·8 in men and 0·7 in women (range 0·5-0·9). The median of energy-adjusted Pearson's correlations for nutrients was 0·8 in both sexes (range 0·6-0·9). The mean Pearson correlation was higher in subjects # 60 years (P¼ 0·02) and in those who declared being 'experienced/expert' with computers (P¼0·0003), but no difference was observed according to educational level (P¼ 0·12). The mean completion time was similar between the two methods (median for both methods: 25 min). The web-based method was preferred by 66·1 % of users. Our web-based dietary assessment, permitting considerable logistic simplification and cost savings, may be highly advantageous for large population-based surveys. Key words: Comparative study: Dietary records: Internet: InterviewCollection of high-quality dietary data in large populations is a priority challenge in nutritional epidemiology. Usual methods for measuring food and nutrient intakes (food records, 24 h recalls, dietary history and FFQ) are based on self-administered questionnaires or interviews by trained dietitians. These methods are complex and costly, requiring substantial logistic resources when applied to large populations (1) . Over the past few decades, new technologies have been developed to enhance accuracy, increase speed and minimise the cost and inconvenience of assessing dietary intake. The use of information and communication technologies for dietary assessment has recently been reviewed (1 -3) . Those reviews stated that new methods hold promise as novel, high-quality, costefficient tools. However, several limitations in previously published validation and comparison studies were identified: many were based on a small sample size (less than 100 subjects), focused on relatively young populations and examined a restricted range of nutrients (mainly macronutrients). Therefore, research into validating technology-based applications for dietary assessment in a variety o...