The monetary value of diets consumed by British adults: an exploration into sociodemographic differences in individual-level diet costs.

Objective: To describe the diet costs of adults in the National Diet and Nutrition Study (NDNS) and explore patterns in costs according to sociodemographic indicators.

Design: Cross-sectional diet diary information was matched to a database of food prices to assign a cost to each food or non-alcoholic beverage consumed. Daily diet costs were calculated, as well as costs per 10 MJ to improve comparability across differing energy requirements. Costs were compared between categories of sociodemographic variables and health behaviours. Multivariable regression assessed the effects of each variable on diet costs after adjustment.

Setting: The NDNS is a rolling dietary survey, recruiting a representative UK sample each year. The study features data from 2008-2010.

Subjects: Adults aged 19 years or over were included. The sample consisted of 1014 participants.

Results: The geometric mean daily diet cost was £2·89 (95 % CI £2·81, £2·96). Energy intake and daily diet cost were strongly associated. The mean energy-adjusted cost was £4·09 (95 % CI £4·01, £4·18) per 10 MJ. Energy-adjusted costs differed significantly between many subgroups, including by sex and household income. Multivariable regression found significant effects of sex, qualifications and occupation (costs per 10 MJ only), as well as equivalized household income, BMI and fruit and vegetable consumption on diet costs.

Conclusions: This is the first time that monetary costs have been applied to the diets of NDNS adults. The findings suggest that certain subgroups in the UK - for example those on lower incomes - consume diets of lower monetary value. Observed differences were mostly in the directions anticipated.