A randomised, double blinded, placebo-controlled crossover design clinical trial conducted at the Mary MacKillop Institute for Health Research (MMIHR, Australian Catholic University) for individuals with overweight/ obesity. This study will measure the postprandial glucose and hormone responses to a high-carbohydrate meal with/ without a liquid tonic drink.

Twenty individuals living with overweight/ obesity will be invited to attend the university laboratories on 2 separate occasions to participate in a postprandial (meal) challenge. Participants will consume the same high-carbohydrate meal on each visit, with or without a liquid tonic drink. This will be a cross-over design study, where participants will consume a placebo drink on the alternate visit. Participants will remain in the laboratory for 3-hours following the meal with a venous cannula in place, and have blood samples taken at regular timepoints. Blood samples will be analysed for glucose and appetite hormones. Participants will also wear a continuous glucose monitor throughout the period which encapsulates both study trials.

Inclusion Criteria:

• Aged ≥30-64 years
• Body Mass Index (BMI) of ≥27.0 kg/m2

Exclusion Criteria:

• younger than 30 or 65 years or older,
• a BMI less than 27.0 kg/m2,
• have an allergy to any of the components in the plant-based tonic (see section 6),
• pregnant or breastfeeding,
• regularly skipping breakfast (i.e. not consuming breakfast on 5/7 days per week),
• any diagnosed metabolic (e.g. diabetes), endocrine (e.g. hyperthyroidism), gastrointestinal (e.g. Crohn's) or cardiovascular (e.g. heart failure) abnormalities,
• on an energy-restricted diet; significant weight fluctuation in the previous 3 months (>5% body weight),
• high alcohol consumption (>14 units/week) (as per Alcohol Drink Guidelines),
• medication that is used to treat blood glucose,
• unable to attend in person testing sessions, or
• unable or unwilling to provide blood samples.

The data that support the findings of this study will be available from the corresponding author for a period of 36 months from publication, upon reasonable request for academic use. The data will not be made publicly available, as it contains information that could compromise research participant consent.

Reasonable requests of data for academic use will be considered. Requests can be made to the corresponding author of the publication. Data will not be made publicly available as it contains information that could compromise research participant consent.

All researchers involved in undertaking the study and analysing the data will be blinded. Participants will be blinded. The dietitian preparing and serving the meal and drink will be unblinded.