Higher Consumption of Ultra-Processed Foods Is Associated with Lower Plant-Based Diet Quality in Australian Adults

Background/Objectives: Plant-based diets are associated with human and planetary health. However, the overall quality of these diets may depend on the proportion of ultra-processed foods (UPFs). This study investigates the association between UPF consumption and plant-based diet quality in Australian adults. Methods: Analysis was conducted on 9111 participants (aged ≥ 19 years) from the National Nutrition and Physical Activity Survey 2011-2012. Food items reported from a 24 h recall were classified using the NOVA system, and the contribution of UPFs to total energy intake was calculated. Plant-based diet quality was examined using the overall plant-based diet index (PDI), healthy PDI (hPDI), and unhealthy PDI (uPDI). Multiple linear regression models were used to examine the association between the UPF intake and PDI, hPDI, uPDI, and their score components. Results: The proportion of energy from UPFs was positively associated with the uPDI (β = 0.80; 95% CI 0.72, 0.89) and negatively associated with the PDI (β = -0.13; 95% CI: -0.22, -0.04) and the hPDI (β = -0.65; 95% CI: -0.73, -0.57). All score components of the PDI, hPDI and uPDI, except whole grains, legumes and fruit juices, significantly contributed to these associations. The sugars and syrups group contributed most to the positive association between UPFs and the uPDI (β = 6.47; 95% CI: 6.07, 6.87) and the negative association of UPFs and the hPDI (β = -6.47; 95% CI: -6.07, -6.87). Conclusions: Higher consumption of UPFs was associated with a lower plant-based diet quality. These findings have implications for the design of dietary interventions that encourage the consumption of minimally processed plant-based foods.