Trends in the quality and processing of plant-based diets in United States youth: a serial cross-sectional analysis...

Although United States youth generally underconsume healthy and overconsume unhealthy plant-based foods, national patterns of plant-based diet quality and relationships with ultraprocessed food (UPF) intake are not well established.

This study aims to examine temporal trends in plant-based diet quality among United States youth, associations with UPF intake, and differences across sociodemographic groups.

We conducted a serial cross-sectional analysis of 24-h dietary recalls from 32,456 participants aged 2-19 y in the NHANES, 1999-2000 through 2017-2020. Plant-based diet quality was evaluated using the overall, healthy, and unhealthy Plant-Based Diet Indices (PDI). UPF intake was estimated as the percentage of total energy from Nova 4 foods. Survey-weighted regression analyses assessed temporal trends, relationships between PDI and UPF, and differences by sociodemographic groups.

Overall plant-based dietary intake increased over time (46.3-48.0 points), accompanied by increases in healthy plant-based dietary intake (46.7-49.4 points) and decreases in unhealthy plant-based dietary intake (51.8-47.8 points) (all P-trend < 0.001). Improvements were not uniform across sociodemographic groups. Overall, plant-based dietary intake was higher among youth from households with higher income, education, and food security. Healthy plant-based dietary intake was highest among females and youth from households with higher income, education, and food security. Conversely, non-Hispanic Black youth had lower healthy and higher unhealthy plant-based dietary intake, with unhealthy intake also higher among older youth and males. Healthy plant-based dietary intake was associated with lower UPF intake and unhealthy intake with higher UPF intake, with both associations strengthening over time.

Plant-based diet quality scores modestly improved among youth, but sociodemographic differences persisted. Healthy and unhealthy plant-based dietary patterns were strongly associated with UPF intake, underscoring the importance of considering diet quality, food processing, and structural determinants of diets and health.