Gestational diabetes mellitus (GDM) is the most common pregnancy complication in Australia, increasing the risk of developing type 2 diabetes tenfold and doubling cardiovascular risk1. Offspring of women with GDM face elevated risks of obesity and metabolic disorders2. Pregnancy presents an opportunity to initiate healthier dietary behaviours, however, evidence on the maintenance of these behaviours postpartum, and their predictors, is limited3. The Healthy Gut Diet (HGD) pilot randomised controlled trial tested a co-designed antenatal dietary intervention4 targeting the gut microbiota to reduce GDM incidence5. This study used Food Frequency Questionnaires at baseline, 36 weeks’ gestation, and 12 weeks postpartum to examine dietary intake and diet quality measured by the Australian Recommended Food Score (ARFS). Quantitative data were analysed with t-tests and linear mixed models. Semi-structured interviews with a subset of HGD participants at 12 weeks’ postpartum explored barriers and enablers of sustained dietary change, analysed thematically and mapped to the Theoretical Domains Framework. At 12 weeks’ postpartum, HGD participants had higher ARFS scores (p=0.004), greater fibre, prebiotic food, and key micronutrient intakes (iron, folate, magnesium), and lower saturated fat consumption compared to usual care. However, no women’s dietary patterns fully aligned with dietary guidelines. Qualitative analysis revealed five themes supporting sustained dietary improvements: person-centred, flexible care; education and knowledge; shared responsibility and social support; physical enablers/barriers; and behavioural/cognitive influences. These findings suggest the HGD intervention facilitated meaningful, sustained postpartum dietaryimprovements, critical for preventing future GDM and cardiometabolic disease. Yet, suboptimal dietary adherence highlights the need for ongoing postpartum dietetic support.