Glucagon-like peptide-1 receptor agonist (GLP-1RA) medications induce substantial body mass loss, however, associated changes in dietary intake during treatment remain poorly understood(1–3). This study explored changes in dietary intake across the first 12-weeks of GLP-1RA treatment among Australian adults living with obesity. A 12-week pre-post, repeated measures study was conducted in adults commencing GLP-1RA treatment. Participants were recruited via social media advertising and referral from St Vincent’s Hospital Weight Management Clinic (Melbourne). Participants completed questionnaires using the REDCap online system, at baseline and after 12-weeks of GLP-1RA use, for self-reported body mass, symptomology, and dietary intake using the Australian Eating Survey (AES)(4) food frequency questionnaire. Change over time were compared with paired t-tests. Significance was set at p<0.05. Of the 37 participants consented, 30 participants commenced the medication (86% female; n = 16 titzepatide; n = 14 semaglutide), with 26 participants completing at least one outcome at 12 weeks. Of the 25 participants (83% of commenced) who reported baseline and 12-week self-reported body masses, body mass at baseline (B) was 103.5 ± 25.6 kg reduced to 94.4 ± 24.8 kg at 12 weeks (Δ-8.8 ± 6.5%, p<0.001). At baseline, 73% (n = 22) completed the AES, with 46% (n = 12) at 12-weeks, where n = 10 (38%) who completed both timepoints are described here. Dietary intake significantly decreased over the 12-week therapy period for total energy (B: 8872 kJ/d, Δ: -1971 ± 1473 kJ/d, p=0.002), carbohydrate (B: 206 g/d, Δ: -49 ± 34 g/d, p=0.001), total fat (B: 91 ± 33 g/d, Δ: -21 ± 22 g/d, p=0.02), saturated fat (B: 37 ± 16 g/d, Δ: -11 ± 11 g/d, p=0.01) and sodium (B: 2118 mg/d, Δ: -672 ± 550 mg/d, p=0.003), with no change to total (B: 95 ± 32 g/d, Δ: -12 ± 29 g/d; p=0.23) or relative protein (B: 0.8 g/kg BW, Δ: -0.04 ± 0.30 g/kg BW, p=0.67) intakes or alcohol consumption (B: 7 ± 9 g/d, Δ: -5 ± 9 g/d; p=0.10). Dietary fibre remained below recommended intakes throughout (B: 23 ± 12 g/d, Δ: -2 ± 5 g/d, p=0.12). The first 12-weeks of GLP-1RA therapy was associated with marked reductions in dietary intake via carbohydrate and fat intakes, but fibre and protein intakes were low (at or below RDI) and did not improve. These findings identify the early treatment period as a critical opportunity for targeted dietary support, with further investigation and consideration of diet quality necessary, to optimise nutritional adequacy during GLP-1RA management of obesity.