Background Sustainable diets can help individuals to reduce their environmental footprint and potentially eat more healthily. However, most studies tend to focus on the greenhouse gas emissions (GHGE) in terms of the environmental impact and dietary cost is not considered. Understanding the sociodemographic determinants of sustainable diets can help in creating feasible suggestions for improvement.

Methods Dietary information from the UK National Diet and Nutrition Survey (NDNS) years 2014–2017 (adults, N = 2165) was used. An average diet was estimated for each participant and a diet quality score. The environmental footprints in terms of GHGE, land use and freshwater withdrawals and the dietary cost were calculated by linking all the consumed food items to their respective values from Poore and Nemecek, 2018 dataset. Diets were classified based on whether they had an acceptable diet quality and whether their environmental footprint and cost was below the median value respectively. Multinomial logistic regression models were used to identify associations between the aspects of diet sustainability and the socio-demographic variables.

Results Men were more likely to consume a diet that was high in GHGE and low quality than a diet of low GHGE and high quality compared to women with odds ratio (OR) 2.35 and 95% confidence intervals (CI) 1.79, 3.08. Vegetarians were more likely to adhere to a diet of low GHGE and high quality than a diet high in GHGE and low quality compared to non-vegetarians with OR 1.78 (95% CI 0.87, 2.65). People aged 45–65 were more likely to consume a diet of higher cost and higher diet quality than younger adults with OR 1.98 (95% CI 1.19, 3.29). Professionals and people in managerial positions were more likely to consume a diet of low quality and high in freshwater withdrawals than those in lower level occupations with OR 1.82 (95% CI 1.21, 2.74). People with higher qualifications were more likely to have a diet of higher GHGE and low diet quality compared to people with no occupation with OR 1.57 (95% CI 0.97, 2.55).

Conclusion Sociodemographic variables are associated with the quality and sustainability of the diet. Employment status and qualifications are positively associated with higher environmental footprint diets across all indicators and cost, whereas women and vegetarians have lower environmental impact diets and cost. Older age groups were associated with higher cost and better quality. Future interventions could help direct individuals to adopt healthier and more sustainable diets.