There is emerging evidence that suggests the gut microbiota of women who are diagnosed with gestational diabetes mellitus (GDM) differs from the gut microbiota of women without GDM. Dietary intake plays a significant role in the composition of the gut microbiota. Dietary interventions targeting the gut microbiota offer promise for mitigating the risk of GDM. The Healthy Gut Diet study is a pilot single blind, two arm, parallel randomised controlled trial (RCT) investigating the effect of a dietary intervention targeting the gut microbiota for preventing GDM. Participants were pregnant women in Queensland with one or more GDM risk factors who enrolled prior to 18 weeks gestation. Dietary intakes were collected using two food frequency questionnaires at baseline and 36-weeks gestation: The Australian Eating Survey (AES) and a modified short dietary questionnaire (SDQ). This preliminary analysis aimed to evaluate changes to dietary intake and diet quality with comparisons between intervention and control participants. This involved a comparison of the mean (SD) Australian Recommended Food Scores (ARFS) and ARFS component scores and SDQ scores at 36 weeks gestation using t-tests. From January 2023 and March 2024, 130 women between 9- and 18-weeks gestation (mean 13 ± 2 weeks) were randomised to usual care or the Healthy Gut Diet intervention. Baseline demographic characteristics showed no statistically significant differences between intervention and control groups. The mean age of participants was 33 (± 4.5) years, parity of 1 and average pre-pregnancy body mass index of 28.2 kg (± 5.9). Thirty-six-week food frequency data was available for 41 control participants and 43 intervention participants (to date). With the exception of ARFS alternatives, there were no statistically significant differences of ARFS (or component) scores at baseline between the two groups. Dietary quality (ARFS) significantly improved in the intervention group compared to controls (mean score 39.7 vs 32.9, p < 0.001). The intervention group successfully increased their consumption of fibre (28.7g vs 24.96 g, p= 0.05) ARFS components of fruits (6.7 vs 5.5, p =0.02), vegetables (14.5 vs 11.8, p=0.003) and grains (6.2 vs 5.3, 0.007), along with increased consumption of fermented (p < 0.001) and prebiotics foods (p < 0.001) compared with controls. This preliminary analysis suggests that the Healthy Gut Diet intervention successfully increased intakes of prebiotic and fermented foods, fibre and overall diet quality compared with controls. This ongoing RCT is an important step to understand the link between the gut microbiota modulation and GDM prevention.