After participants returned the 24HR and a consent form they were sent an invitation to a health check. Over 26,000 questionnaires were completed and returned.
The FFQ is designed to measure a participant's usual food intake during the previous year. It is also possible to obtain food group data from the FFQ.
The questionnaire is a 10-page A4 document, consisting of two parts:
Part 1, the main part, contains a list of 130 foods. For each item on the list, participants are asked to indicate their usual rate of consumption choosing from nine frequency categories. The categories range from "never or less than once/month" to "6 times per day". The servings are specified in terms of units or common portions (e.g. one apple, one slice of bread) or household measures (e.g. glass, cup, spoon). An average portion size was assigned to each questionnaire item.
Part 2 includes a set of additional questions on type and brand of breakfast cereal; type of fat used in frying, roasting, grilling or baking; and the amount of visible fat on meat. These questions are linked to relevant items on the list and used to help categorise breakfast cereals and total fat and fatty acid consumption respectively. A further question on milk is also found in part 2, requesting information on the type and quantity of milk consumed.
The FFQ data are entered into an Oracle based entry system. They are processed using the CAFE program (Compositional Analyses from Frequency Estimates) which converts the frequency category for each of the 130 food categories into an amount for each nutrient profile and from that calculates average daily nutrient intake. During the processing of the FFQ, the free text relating to milk, fat and breakfast cereals, from part 2 of the FFQ has to be matched and converted into the appropriate nutrient database code. Occasionally participants did not put a tick on each line or made multiple ticks on a single line. These responses are given specific codes during entry and treated as missing data by the CAFE program. Individuals with more than 10 missing lines of data are excluded. The extreme top and bottom 0.5% of the ratio of energy intake to estimated basal metabolic rate was used to exclude extreme outliers of nutrient intakes.
For further information on the nutritional analysis of the EPIC FFQ, see CAFE and FETA publications.
A further FFQ was collected at the second and third health checks.