This report describes the changes in dietary methodology in the National Diet and Nutrition Survey rolling programme (NDNS RP) implemented from fieldwork year 12 (2019 to 2020), sets out the plan for evaluating the impact of the changes on participation in the survey and the resulting data, and presents findings from the first stage of this evaluation.

The NDNS RP is a continuous cross-sectional survey, jointly funded by Public Health England and the UK Food Standards Agency and carried out by a consortium comprising NatCen Social Research and the MRC Epidemiology Unit, University of Cambridge. It is designed to assess the diet, nutrient intake and nutritional status of the general population aged 1.5 years and over living in private households in the UK.

For fieldwork years 1 to 11 (2008 to 2019) dietary assessment was based on a food diary completed over 4 consecutive days. This used paper-based open-text entry by participants with review by interviewers and retrospective coding of foods and portions by trained coders. In 2018 the decision was taken to move to an automated data collection method with the potential to improve data quality and reduce costs. Following a review of available automated tools and full evaluation of 3 shortlisted tools, Intake24 was selected to replace the paper food diary in the NDNS RP.

Intake24 is a web-based automated self-administered 24-hour dietary recall tool. Participants are asked to record everything they ate and drank the previous day. The tool includes an embedded database of foods with linked portion sizes and corresponding nutrient composition data from which dietary intakes are automatically calculated.

A number of developments were made to Intake24 and to the underlying data before it was used in NDNS, to enable it to meet requirements. These included updates to the tool functionality and addition of questions to provide supporting contextual information. Work was also undertaken to update the food lists from which participants select the foods and drinks they consumed and to rationalise and update the linked nutrient composition information in the NDNS nutrient databank. This aimed to achieve a comprehensive and up to date database of foods to adequately reflect the heterogeneity of foods in the UK while remaining manageable for participants. This included creation of new generic food codes, mainly for sandwiches and salads which were not required before Year 12 as these items were previously coded as individual components.