The goal of this clinical trial is to examine the impact of food derived bacteria on gut microbiome composition and host health. The main questions it aims to answer are:

• what is the the rate of gastrointestinal colonisation of food derived bacteria?
• what is the contribution of food derived bacteria to gut microbiome stability?

Participants will complete a cross over feeding study of dietitian designed meals of known microbial load and will be asked to provide stool and blood samples for analysis.

To understand the role and stability of food derived bacteria in impacting microbiome composition, 20 healthy participants will be recruited for this single site double blinded randomised controlled crossover pilot trial. The study is divided into four 14 day diet phases - baseline habitual, specified diet 1, habitual washout and specified diet 2. Participants will be randomly assigned to receive a microbial or non-microbial diet in specified diet 1 phase. Each participant will then crossover to receive the alternative diet in the specified diet 2 phase. The microbial and non-microbial diets will be identical except for the removal of naturally occurring food derived bacteria in non-microbial diet. At the commencement of the study and at the end of each diet phase, participants will attend a research clinic to undergo comprehensive clinical and anthropometric assessment and dietary evaluation.

Inclusion Criteria:

• Have no genetic conditions (e.g. Prader Willi or Down's Syndrome)
• Not diagnosed with a significant medical conditions (e.g. irritable bowel syndrome, inflammatory bowel disease or type 1/2 diabetes)
• Do not require drug-therapy (e.g. steroids or insulin or antibiotics)
• Not taking dietary supplements, probiotics, prebiotics, symbiotics or fibre supplementation
• Any condition that will affect participation in the study
• Not pregnant, planning a pregnancy or breastfeeding
• Able to complete a two-month dietary study and agree to eating all meals provided
• Have no dietary allergies or dietary restrictions that prevent consumption of provided study meals
• Open bowels regularly - mostly daily
• Able to read, write and understand English

Exclusion Criteria:

• Dietary concerns identified by dietitian
• Aged less than 18 years and older than 65 years
• Diagnosed with a medical condition that requires drug therapy
• Taking medications or supplements known to alter gastrointestinal microbiota
• Women who are pregnant, planning a pregnancy or breastfeeding
• Anyone with a diagnosed gastrointestinal condition/disease e.g. irritable bowel syndrome or inflammatory bowel disease
• Known dietary allergy and/or intolerance, follows a vegan or vegetarian diet, or has coeliac disease
• Anyone with a preference for specific food avoidance or exclusion of certain ingredients in habitual diet
• Unable to tolerate blood collection procedures
• Unable to provide regular stool samples throughout the study

Applications made for reasonable access to de-identified study data will be made on a case-by-case basis by the study team. Data-specified appropriate analysis will be determined when required. Applications for data accessibility will be made on a case-by-case basis by study team.

Accessibility to individual participant data (IPD) and supporting information will be determined at a later date and on a case-by-case basis

Accessibility will be assessed on a case-by-case basis