Trajectories of plant-based dietary patterns and their sex-specific associations with cardiometabolic health among young Australian adults

Background: Plant-based diets are associated with favourable cardiovascular health markers. Although increasingly consumed among younger demographics, it is unclear how plant-based diet quality tracks from adolescence to young adulthood, and how this impacts cardiovascular health later in life. Thus, this study aimed to explore trajectories of plant-based dietary patterns from adolescence to young adulthood and investigate associations with cardiometabolic health markers in young Australian adults. Methods: Longitudinal data from 417 participants from the Raine Study were included. Semi-quantitative food frequency questionnaires conducted at 14, 20, and 27 years of were used to derive three plant-based diet quality index scores: an overall plant-based diet (PDI), a healthy plant-based diet (hPDI), and a less healthy plant-based diet (uPDI). Markers of cardiometabolic health included waist circumference, blood lipids, and blood pressure obtained at 14 and 28 years of age. Group-based trajectory modelling was used to describe plant-based diet quality trajectory groups from adolescence to young adulthood. Multivariate linear regression models were used to investigate associations with cardiovascular health markers. Results: Plant-based diet quality trajectory groups were different by sex, but remained relatively stable over the life stages, with participants remaining either above or below average diet quality at all time points. Associations with cardiovascular health outcomes differed between the sexes, with the hPDI having the greatest number of associations for females, and the uPDI for males. Being female with a higher hPDI score was associated with lower insulin (β = -1.11 (95% CI -2.12, -0.09)), HOMA-IR (β = -0.25 (95% CI -0.48, -0.01)), systolic blood pressure (β = -2.75 (95% CI -5.31, -0.19)), and hs-CRP (β = -1.53 (95% CI -2.82, -0.23)), and higher HDL-cholesterol (β = 0.13 (95% CI -0.03, 0.23)) compared to females with lower hPDI scores. Being male in the higher scoring uPDI group was associated with higher waist circumference (β = 3.12 (95% CI 0.61, 5.63)), waist-to-height ratio (β = 0.02 (95% CI 0.01, 0.03)), insulin (β = 1.54 (95% CI 0.33, 2.76)), HOMA-IR (β = 0.35 (95% CI 0.07, 0.63)), and hypertension status (β = 6.60 (95% CI 1.04, 42.00)) when compared to the lower scoring uPDI group. Conclusions: This study provides new insights into how plant-based diets track across adolescence into adulthood, impacting on cardiometabolic risk factors differently for males and females. Findings highlight the importance of early sex-specific interventions in adolescence to reduce future risk of cardiovascular-disease.