Feasibility and measurement error in using food supply data to estimate diet costs in Canada

Abstract

Objective: The cost of food is a key influence on diet. The majority of diet cost studies match intake data from population-based surveys to a single source of food supply prices. Our aim was to examine the methodological significance of using food supply data to price dietary intakes. Methods: Nationally representative 24-h dietary recall data from the 2015 Canadian Community Health Survey-Nutrition (CCHS-N) was matched to the 2015 Canadian Consumer Price Index (CPI) food price list. Proportions and means of reported intakes covered by the 2015 CPI price list were used to compare reported intakes of food groups and food components of interest and concern overall and by quartile of CPI coverage. Setting: Canada. Participants: In total, 20 487 Canadians ages one and older. Results: The CPI covered on average 76·3 % of total dietary intake (g) without water. Staple food groups that were more commonly consumed had better CPI price coverage than those less commonly consumed. Yet some food groups (vegetables, additions and sweets) that were also commonly consumed by Canadians were not well covered by price data. Individuals in the poorest CPI coverage quartile reported consuming significantly greater gram weight (g), dietary fibre (g) and energy (kcal) as compared with those with the best coverage. Conclusions: Differential CPI price coverage exists among food components and commonly consumed food groups; additionally dietary intake differs significantly in the population by CPI coverage. Methodological refinements are needed to better account for error when using prices from food supply data to estimate diet costs.