Reexamining the relationship between energy density and food price

Background: The inverse relationship between energy density (kcal/g) and energy cost (price/kcal) has led to the conclusion that snacks (cookies, chips) are inexpensive relative to produce (fruit, vegetables).

Objective: This paper demonstrates the weakness of this measure of food price, and presents an analysis of alternative measures of food price and energy content.

Design: Observational data were collected on food items available at an online supermarket. Total price ($), total energy (kcal), total weight (g) and serving size (g/serving) were obtained and used to calculate measures of energy content (energy density, kcal/serving) and food price (total price, price/g (gram price), price/serving (serving price), and energy cost). Student's t-tests were used to compare mean measures of food price of produce and snacks. Correlation analysis was used to examine the relationships between measures of food price and energy content.

Results: The relationships between different measures of food price and energy density were either positive or flat. Total price was positively related to energy density and kcal/serving. The relationship between gram price and energy density was either flat or positive, depending on the sample of foods. There was no relationship between serving price and kcal/serving. Mean energy cost was highest for produce, while total price was lowest for vegetables, serving price was highest for fruit, and gram price was highest for cookies.

Conclusions: These findings suggest the relationship between food price and energy content and the relative price of snacks and produce depend wholly upon the measure of price under consideration.