PREDICT 2: Personalized Responses to Dietary Composition Trial 2

Choice of design: The study is a single arm mechanistic intervention study. Study population: Participants will be recruited through online and offline advertisements, and through health professionals. Screening Assessment: Prospective participants will be selected based on the defined inclusion and exclusion criteria by the study management team. Screening will be online and via phone. Prospective participants will be booked in to start their study period and will receive a study kit by post. Study duration: Each participant will take part in the study for a period of up to 12 days. Dietary intervention: The dietary intervention will be carried out on up to 8 days within the 12-day study period. On day one, participants will be asked to collect biological samples and fit wearable devices (glucose monitor and physical activity tracker). Over the following consecutive days, each participant will be instructed to eat up to 8 standardised meals for breakfast, which must be their first meal of the day. On up to 3 of the days the participants will also be asked to eat a standardised lunch. Participants are free to eat whatever they wish at all other times. The standardised meals will be provided to all participants by the study team via post. The foods included as part of these meals will be foods that are commonly consumed and can be made from products sold in US supermarkets. Participants will be reassured that the amount of food will be designed to ensure a stable body weight over the course of the study. Participants will be asked to consume the entire amount of food indicated for the standardised meals and to record any left-over food via a digital app for which training will be provided at the start of the study. Following completion of standardised meal days, participants are free to eat and drink whatever they wish and will be asked to track all meals, snacks and drinks on their digital app. Participants will also be advised not to change their physical activity patterns during the course of the study. The 12th day of the study involves a visit to a medical clinic where participants will provide a fasted blood sample. Regular contact will be made with the participants via phone, their app and text messages for the period of the intervention to encourage compliance and answer any queries. Anthropometry: The participant will be instructed to measure their weight, height, waist and hip circumference. Dietary and Lifestyle: Participants will be asked to complete a baseline questionnaire online, as well as a diet history questionnaire with portion sizes about the month preceding their study period. They will be asked to record on a daily basis their dietary, activity, and psychological data (e.g. hunger) using a digital mobile phone app. Lifestyle information (such as sleep and exercise) will be monitored using digital wearable devices. Training in all apps and equipment will be given through written and online instructions and via communications with the study support staff. Digital devices: Participants will be asked to record daily dietary and activity information using digital apps and lifestyle information will be monitored using digital wearable devices. The continuous glucose monitor (Freestyle Libre, CGM) provides continuous glucose profiles for up to 14 days. The CGM will be inserted on the back of the upper arm, one day before participants begin dietary intervention. This will measure subcutaneous interstitial fluid glucose concentrations every 5 minutes. The CGM will be removed at the end of the intervention period by the participant. A contact number will be made available to participants for any inquiries or if any problems arise. Data from the CGM will be downloaded, and glucose profiles will be evaluated on the basis of data collected. Blood samples: The participant will collect postprandial blood on 2 days using finger-prick blood sampling. They will also provide a fasted blood sample after the study period to measure their baseline metabolomic profile. Digital app: Participants will be asked to download an app designed specifically for this study, which provides diet \& activity logging functionality similar to widely used existing apps such as MyFitnessPal. Participants will be asked to record and monitor the following information via the digital app and wearable devices, on a daily basis: * All food and drink they consume, with serving sizes and photos * Sleep and physical activity patterns, including exercise * Hunger and alertness ratings * Psychological feeling of energy and mood * Prescription and over-the-counter drug consumption The app will be available in versions for both iOS and Android operating systems, and will support a wide range of mobile phone models as expected across the participant population. The app will synchronise remotely with backend database servers, over an encrypted and authenticated API, and will support offline operation for when patients wish to record an entry without network coverage. This continuous background synchronization means that it will not be necessary to explicitly download data from the phone at the end of the study. Following the 2020 pandemic of COVID-19, participants are asked to use the COVID-19 Symptom Tracker app to record their physical health symptoms, or lack thereof, attributable to COVID-19, as well as demographic and other health information to track the spread of disease in real time, and to potentially reveal risk factors for infection and severe illness. Subcohort: An opt-in follow-on study will be offered to participants to follow dietary guidance from the ZOE app based on their Predict 2 results. During the first 2 to 4 weeks, participants will be given dietary guidance to follow from the ZOE app. Thereafter, for a period of up to 12 months, participants will be asked to report on outcome measures at regular intervals (monthly). Outcome measures will be reported before, during and after the 2 to 4 week period and include weight, bristol stool, bowel habits, hunger, energy, alertness, stress, mood, activity, adherence to dietary advice, and app usage. The data will be used to test the efficacy of the ZOE dietary advice in promoting weight loss and improvement of overall health, and may be stratified by age, sex, BMI, adherence and/or motivation to take part in the PREDICT 2 study.