Cost of diets
The monetary cost of the reported diets was estimated by
attaching a food price vector to the FFQ’s nutrient composition
database as described previously (20). Retail prices for each of
the 289 component food items in the FFQ were obtained by
using standardized and published price collection methods (21).
In brief, each food and drink in the FFQ was priced by using
MySupermarket.com, a website for comparing supermarket food
prices nationwide in the United Kingdom. For each of the 289
items in the FFQ, the lowest, nonsale price was selected from
among the 5 nationwide retailers represented on the website at
that time (June 2012): Tesco, Sainsbury’s, Asda, Waitrose, and
Ocado, which together had a 68% market share in 2012 (22).
For packaged goods, including most fresh produce, the
package size in the middle of the range was typically selected. If
only 2 package size options were available, the larger was chosen.
As described previously, prices were adjusted for preparation and
waste (21) to yield an adjusted food price of £/100-g edible
portion. The addition of this new variable to the EPIC-Norfolk
food and nutrient database (16) allowed the derivation of dietary
cost for each participant. The variable associated with each individual’s
diet was cost per day (£/d).