The aim is to test if dietary supplementation with prebiotics reduces measures of anxiety in healthy human participants with high self-reported levels of anxiety. Study will test for an effect on behavioural, neuroendocrine and brain imaging markers of anxiety.

Inclusion Criteria:

• Trait anxiety levels > 40 on STAI trait inventory
• Participant is willing and able to give informed consent for participation in the study
• Not currently taking any psychoactive medications

Exclusion Criteria:

• Pregnant participants
• No contraindications to prebiotic administration
• Antibiotic, probiotics and/or prebiotic treatment in at least the two previous months.
• Participants who are taking any other food supplements that, in the opinion of the Investigators, may affect the results.
• Participants who are taking any medications that, in the opinion of the Investigators, may affect the results.
• Any significant change in diet which, at the discretion of the Investigators, may affect the results.
• Participants who have recently participated in another research trial which, at the discretion of the Investigators, may affect the results.
• A history of dementia, traumatic brain injury or stroke.
• Anyone who is unable to perform the behavioural tasks.
• Current use of any psychoactive medication.
• Current use of psychological treatment.
• Anyone who does not have adequate understanding of English, sufficient to give informed consent.
• Any person who has a history of drug abuse or a previous history of a neurological, or has a history of neurosurgical procedure is excluded as they may be at increased risk of epilepsy and data collected may be influenced by their condition.
• Anyone with any metal implants or implantable device would be excluded from any brain imaging studies as indicated by the MRI safety screening form.

The study staff will ensure that the participants' data are safeguarded. The study will comply with the Data Protection Act, which requires personal data to be anonymised as soon as it is practical to do so. Students and collaborators may be given access to fully anonymized data under the supervision of the named investigators. Some peer-reviewed journals require submission of anonymised data that may also be uploaded to other data sharing initiatives. Access may be given to responsible members of the University of Oxford for the purposes of monitoring or audit. The participants' consent will be sought if this is to occur.

Both intervention and placebo products are similar in colour, texture, and taste. A third party, independent of the daya-to-day research coordinator, will randomise treatments.