The relationship between diet costs and dietary adequacy: A scoping review of measures and methods with a focus on cost estimation using food supply data

Background: 'Diet cost' refers to a methodological approach developed by Drewnowski and colleagues to estimate individual daily diet costs, where cost vectors are derived by matching prices from food supply data to the food sources of reported intakes from dietary assessment tools. The dietary assessment method and food price collection approach have been found to vary diet cost estimates. There is a need to better understand how food supply prices might be better standardized and attached to price individuals' diets.

Objective: To conduct a scoping review to examine Drewnowski's diet cost method, with a focus on a detailed description and charting of cost estimation measures and methods used to price individuals' consumed diets.

Methods: Five databases were searched from the inception of each database through to March 2023. Included papers comprised analyses of individual-level dietary assessment data matched to food prices to assign estimates of individual daily diet costs.

Results: 55 articles were included, published between 1999 and 2022 from 17 countries. In all studies, cost estimates were intended to be representative of price exposures among individual respondents' dietary assessment data. All studies derived cost estimates from separately collected food prices. 34 (62%) of included papers collected food prices from retail (supermarket) audits. A minority of studies (19, 35%) reported the number of food prices used to cost diets, and those varied widely, ranging from 57 to nearly 4,600 distinct foods priced per study.

Conclusions: In the absence of a standardized approach to study the relationship between diet costs and dietary adequacy, this scoping review has described methodological concepts and parameters used to price individuals' consumed diets. Our review shows that despite common arithmetic to calculate cost vectors, there is substantial variation in the methods used to select and attach prices from the food supply to self-reported dietary intake assessments.