NSHD: estimation of nutrient intake
Nutrients from the food diaries were estimated following the approach outlined in Estimating nutrient intakes from DATs.
The coding of the NSHD dietary diary data has advanced over the years through the development by MRC Human Nutrition Research in Cambridge of two in-house programmes: Diet In Data Out (DIDO) and Diet in Nutrients Out (DINO) [37, 38].
In 1982, the dietary data were originally manually coded in Bristol [39]. DIDO was developed to code the 1989 diary data and was also used to code the 1950 24-hour recall and to convert the previously coded 1982 dietary dairy data and the 1999 diet diary data.
DIDO
DIDO is a specially developed data entry system written in the C programming language [37]. It is designed around a hierarchical food menu consisting of nearly 2000 food and drink items arranged by major food groups and sub-groups as listed in food composition tables. It generates a food code and associated weight in grams for each item recorded.
The food codes are taken from the British food composition tables and the portion weights can be chosen from a list of standard weights attached to descriptions appropriate for each food e.g. teaspoon, tablespoon, medium slice etc. These portion weights vary according to the type of food and can be informed by manufacturers information.
Once each diary is coded using DIDO, it is linked to British food composition tables [40-43] using a separate in-house suite of programmes to estimate nutrient intakes.
Since the nutrient composition of food items were likely to have changed over time, time-appropriate food composition tables were used to estimate the nutrient intake for each diary as outlined previously [44].
For the 2006-2011 dietary data coding, DIDO was updated to a Microsoft Access based system, DINO [38]. DINO includes >6000 food items with their estimated portion sizes and is directly linked with food composition tables to estimate nutrient intakes [38].
The previous diet diaries have now been transferred to DINO; however, there is some minor discrepancy in how the foods were categorised between the years. Vitamin and mineral supplements were coded separately. There were some specific elements of the 1950 24-hour recall that required special attention when coding and these are outlined in detail by Prynne et al. [35, 36].
It is not possible to estimate nutrient composition from the 2014-2015 diet-related questions due to insufficient detail captured.