Understanding how Australian adults choose and follow very low calorie diet (VLCD) programs, their food and eating behaviours, and associated effects on self-perceived physical and mental health

Two groups of participants will be recruited: • Group 1: Participants who have used the OPTIFAST VLCD Program within the last 4 weeks, daily for 7 or more days in a row but do not meet the eligibility criteria for Group 2. Participants in this group will not answer all survey questions. • Group 2: Participants who have used the OPTIFAST VLCD Program more than a month, at least daily for 4 or more days/week and either continue to use or ceased use within the last 4 weeks. Participation involves completion of a once-off online survey. The online survey involves multiple components including: - Demographic questionnaire - OPTIFAST VLCD program use questionnaire - Phyiscal activity questionnaire - Health-related quality of life questionnaire - Weight-related quality of life questionnaire - Eating behaviours questionnaire - Mental health questionnaire - Self-efficacy questionnaire They survey, including all questionnaires within the survey, will take 20 to 30 minutes in total to complete. Convenience and snowball sampling will be used to recruitment participants via an advertisement platform including: QR Codes on flyers placed in pharmacies, advertisement with electornic links to the survey on the OPTIFAST Website, social media (private posts and paid posts), and websites/electronic networks of health care professionals. At the completion of the questionnaire, if any responses indicate the participant may be using OPTIFAST unsafely, e.g. if they have a low BMI or are experiencing side-effects, they will recieve a message at teh end of the survey recommending they speak to their GP about their use of the OPTIFAST program. Participants will not be emailed a copy of their responses.