Pilot Test of a Diet Cost Calculation Process for Use in Economic Evaluations of Dietary Interventions

Nutrition is a significant modifiable risk factor for many illnesses. One often-cited barrier to diet change is the perceived cost of healthy food. While many diet diary templates exist, none have been developed to capture the data needed for calculating the cost of a diet consumed during a diet intervention study.

The objective of the present project was to develop and pilot test (1) a tailored diet diary template with instructions, and (2) alternative approaches for calculating diet cost. We created a draft diet diary and instructions which were used by participants. We used those data to test the feasibility of calculating weekly diet cost. Two methods were used: calculation of the cost of the actual price of the items purchased, and standardised prices. Acceptability was assessed by conducting participant interviews and the feedback that was provided was used to revise them. The methods to calculate costs were compared in terms of feasibility and researcher time needed.

Of the 15 participants enrolled, 14 completed the interview. All participants reported that the process was acceptable or highly acceptable. Participant feedback was used to guide changes to the diet diary and instructions. Costs were calculated for 85.3% to 96.3% of food items. The researcher time needed to complete each method per participant, per week was 5 to 6.5 h. Participants who gave feedback confirmed that the edits addressed their previous concerns.

Overall, the diet diary and instructions were acceptable to participants who are women and feasible for the collection and costing of diet data in Canada.