The aim of this study is to determine whether encapsulation of probiotic bacteria using natural plant protein can enhance bacterial colonisation. Lactobacillus rhamnosus is an ideal strain for the intervention, as it has been shown to affect overall gut health, gut-brain axis, and brain function.

Twenty-five participants aged 25 to 65 years will be recruited and assessed on four occasions to compare the blood and faecal effects of a 28-day ingestion of a yoghurt beverage with and without the probiotic strain of interest. The study window will be 70+/13 days.

The current study will provide important information on the physiological function of probiotics in the small bowel. Understanding the underlying physiological effects of targeted probiotic delivery to the intestine and the impact on the microbiome is important for health outcomes.

The investigators plan to assess the gut microbiome and changes in probiotic diversity at the end of a course of a beverage containing encapsulated Lacticaseibacillus rhamnosus, compared to those at the end of a course of the same beverage without probiotics.

This is a randomised, double-blinded, placebo-controlled crossover study. Twenty-five healthy men and women with a body mass index (BMI) between 18.5-31.9 kg/m2, aged 25-65 years, will be recruited and randomised to a commercial fermented (yoghurt) drink containing a) encapsulated probiotics consisting of Lacticaseibacillus rhamnosus, or b) a non-probiotic fermented (yoghurt) dairy drink (control). The number of participants includes a 10% drop-out rate.

Each participant will be studied on four occasions in random order following a crossover design. Each will receive a 200 ml beverage containing yoghurt per day for 28 days, either a) fortified with 1 billion probiotics contained in pea protein capsules or b) the control beverage (same yoghurt without probiotic). Faecal samples will be collected on four occasions: at baseline, and at 28, 42 and 70 days after baseline.

The current study will provide important information on the physiological function of probiotics in metabolic and inflammatory biochemical parameters, as well as in their capacity to colonise the gastrointestinal tract.

Inclusion Criteria:

• Capacity to obtain and sign informed consent before any study-related procedure
• BMI range 18.5-31.9 kg/m2
• Willing to abstain from regular consumption of probiotic supplements or food products containing probiotic bacteria (including fermented food and beverages).
• Willing to abstain from regular consumption of supplements and medications known to alter gastrointestinal function or inflammatory status during the study.

Exclusion Criteria:

Participants who meet any of the following criteria will be excluded:

• Smoking
• Substance abuse
• Pregnancy
• Diagnosis of type 1 and/or type 2 diabetes
• Current (or within the last 4 weeks prior to study start) use of probiotic supplementation.
• Immobile (defined as the inability to participate in all study-related procedures)
• History of complicated gastrointestinal surgery
• Diagnosed with inflammatory bowel disease (IBD)
• Current diagnosis of psychiatric disease/s or syndromes
• Current diagnosis of neurodegenerative disease
• Systemic use of antibiotics and/or steroid medication in the last 4 months prior to inclusion
• Use of any non-steroidal anti-inflammatory drug (NSAID) more than 3 times a week for the last 2 months
• Consumption of any NSAID within 7 days of study start
• Any condition which could substantially interfere with intestinal barrier function (e.g. gluten sensitivity, lactose intolerance, celiac disease, IBS, IBD) or in any other way with the outcome of the study, as decided by the principal investigator's discretion
• Regular smoking, use of snuff, nicotine, cannabidiol narcotics/supplements, or e-cigarette use
• Drinking more than 9 standard cups of alcohol per week and/or more than 3 standard cups of alcohol per occasion
• Regular use, for more than three times a week for the last 2 months and/or 7 days prior to inclusion, of medications which, according to the principal investigator, can have an anti-inflammatory effect or affect in any way the intestinal barrier function or have an impact on the study analysis (such as laxatives, anti-diarrheal, anti-cholinergic, etc.)
• After being included in the study, starting any medication or treatment that could potentially influence the study participation and/or study analysis.

This study will be carried out in a single center. Therefore, fecal samples sent for microbiota analysis and data for statistical analyses will be identified by numbers allocated in the protocol and not contain identifiable information.