Eating Behaviour Before, During, and After Obesity Medication

This study will examine how eating behaviour changes during the first 18 months of treatment with obesity medications in patients attending the St Vincent's Healthcare Group obesity service. Obesity is increasingly understood as a chronic, relapsing, multifactorial disease that requires long-term management rather than short-term advice alone. Newer anti-obesity medications, particularly glucagon-like peptide-1 receptor agonists and related therapies, have improved weight-loss outcomes and altered the experience of hunger, fullness, food reward, and meal size for many patients. However, while weight reduction is well described in the literature, less is known about how patients themselves experience eating behaviour over time as treatment progresses from initiation to active weight loss and then towards weight maintenance. This study is designed to address that gap by exploring the lived experience of appetite and food-related behaviour across clinically meaningful stages of treatment. The study will use a longitudinal mixed-methods design. Thirty participants aged 16 to 80 years with a body mass index above 27 kg/m2 who are commencing weight-loss medication as part of routine care will be recruited. The sample size includes an allowance for a modest dropout rate over the study period. Participants will be followed at four time points: baseline, approximately 3 months after treatment initiation, around 12 months, and at 18 months, with a visit window of plus or minus 13 days. These time points were selected to reflect distinct phases of treatment. Baseline will capture pre-treatment or very early-treatment experience. Three months is expected to reflect a period of early therapeutic response, when medication effects on appetite may be most noticeable. Twelve months is likely to represent a later phase, when weight loss may be slowing and some patients may be approaching their lowest weight. Eighteen months is intended to capture maintenance or stabilisation, when behavioural changes may differ from those seen earlier in treatment. Data collection will include both questionnaires and semi-structured telephone interviews. The questionnaire component will measure key aspects of eating behaviour, including hunger, fullness, food thoughts, portion size, and palatability. Repeated administration at each study time point will allow changes in these behaviours to be tracked over time. The interview component will provide a richer understanding of how participants describe and interpret their experiences. All interviews will be conducted by one co-investigator using the same core interview guide to ensure consistency. Open-ended questions will allow participants to describe changes in appetite, eating patterns, cravings, meal satisfaction, food preferences, and daily routines in their own words, while additional probing may be used to clarify how these experiences evolve through treatment. Interviews are expected to last 15 to 45 minutes, will be audio-recorded with verbal confirmation, and transcribed for analysis. The central research question is how hunger, fullness, food thoughts, portion size, and food palatability change over time during treatment with obesity medications. The hypothesis is that appetitive and consummatory behaviours will decrease from baseline to an early low point, particularly around 3 months, and may then gradually rise again as treatment continues, before stabilising during a later maintenance phase. This pattern would reflect the possibility that the strongest appetite-suppressing effects occur early, followed by behavioural and physiological adaptation over time. At the same time, the study recognises that patients may not all follow the same course, and individual variation will be an important part of the analysis. Quantitative data will be used to describe behavioural trends across time points, while qualitative data will be analysed thematically to identify recurring experiences, challenges, and adaptations. Integrating these two forms of data will strengthen the study by linking measurable change with patient perspective. The study is expected to provide clinically useful insight into how anti-obesity medications influence the lived experience of eating, and how this may change between the active weight-loss phase and maintenance. By focusing on patient-reported hunger, satiety, food preoccupation, portion size, and palatability, the research may help clinicians better understand when patients need additional support, how expectations can be managed, and what aspects of treatment are most important for long-term success. The findings may also contribute to more personalised obesity care by highlighting the behavioural dimensions of treatment that are not captured by weight change alone.