Evaluation of changes in dietary methodology in the National Diet and Nutrition Survey rolling programme from year 12 (2019 to 2020): stage 2

This report presents findings from the second stage of evaluation of the changes in dietary assessment methodology in the National Diet and Nutrition Survey rolling programme (NDNS RP) implemented from fieldwork year 12 (2019 to 2020).

The NDNS RP is a continuous, cross-sectional survey, jointly funded by OHID, DHSC and FSA, and carried out by a consortium comprising NatCen and MRC Epi. 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 NDNS fieldwork years 1 to 11 (2008 to 2019), dietary assessment was based on a paper food diary completed by participants over 4 consecutive days with open text entry, review by interviewers and retrospective coding of foods and portions by trained coders. In 2018, following a review of available automated tools, the decision was taken to move
the dietary assessment method to Intake24, a web-based automated self-administered 24-hour dietary recall tool. Data collection using Intake24 began in October 2019 (fieldwork year 12) following a dress rehearsal and developmental updates to the tool.

A first stage evaluation report was published in September 2021 based on data collected from October 2019 to March 2020 (year 12). While based on a limited amount of data, the findings indicated that the introduction of Intake24 was compatible with NDNS RP requirements. Overall comparability with the previous data collected using the food diary appeared to be good; however there was an observed fall in the percentage of participants who reported taking supplements and a drop in the percentage of consumers and amounts consumed for some foods, in particular vegetables, fish, and for younger children, sugar confectionery and buns, cakes and pastries.

This report, the stage 2 evaluation, updates stage 1 and is based on data collected from October 2019 to May 2022. This includes the data from year 12 (October 2019 to March 2020) and new data from years 13 and 14 (October 2020 to May 2022). Data from the NDNS follow-up study during COVID-19 (August to October 2020) (PHE, 2021b) has also been used to fill in the time gap left by the main fieldwork suspension. This stage 2 evaluation includes:

• findings of the doubly labelled water (DLW) study to assess misreporting of energy intake. The DLW method measures total energy expenditure in free-living individuals over 1 to 2 weeks. This is compared with reported energy intake
• assessment of how the new fieldwork model is working in terms of participation rates for dietary recalls and spread across days of the week
• quality measures for use of Intake24 including completion time and number of foods reported
• analysis of the impact of changes to the dietary assessment method on time trends for foods and nutrients