This is a 3-arm, parallel-group, randomized, double-blind, placebo-controlled pilot trial. Sixty adults presenting with depressive symptoms will be randomly allocated to one of 3 groups comprising (1) Bifidobacterium adolescentis or (2) Lactocaseibacillus rhamnosus LGG and Bifidobacterium BB-12 or (3) a placebo for 12 weeks.

At baseline (Visit 2), midpoint (Visit 3) and end-of-study (Visit 4) visits, participants meeting eligibility criteria will complete the BDI-II, BAI, DASS-21 and PROMIS Sleep questionnaires and blood samples will be collected for biomarker assessments. Fecal samples will be collected prior to the baseline and end-of-study visits for microbial profiling.

This is a 3-arm, parallel-group, randomized, double-blind, placebo-controlled pilot trial. Sixty adults presenting with depressive symptoms will be randomly allocated to one of 3 groups comprising (1) Bifidobacterium adolescentis or (2) Lactocaseibacillus rhamnosus LGG and Bifidobacterium BB-12 or (3) a placebo for 12 weeks.

At screening (Visit 1), the study design will be explained to participants, following which signed GDPR and study informed consent will be obtained. Participants will be assessed for eligibility, medical history and concomitant therapies.

At baseline (Visit 2), midpoint (Visit 3) and end-of-study (Visit 4) visits, participants meeting eligibility criteria will complete the BDI-II, BAI, DASS-21 and PROMIS Sleep questionnaires and blood samples will be collected for biomarker assessments. Fecal samples will be collected prior to the baseline and end-of-study visits for microbial profiling.

Inclusion Criteria:

1. Generally healthy adults (male and female) 18 to 65 years
2. Currently experiencing depressive symptoms as indicated by a score of between 20 and 40 on the BDI-II at both the screening and baseline visit
3. Body mass index (BMI) between 18.5 and 30.0 kg/m2
4. Non-smoker
5. No plan to change dietary or exercise habits during the study period
6. No recent history (within 3 months) or plan to commence new treatments over the study period
7. Willing and able to take probiotic/placebo regimen for 12 weeks
8. Understand, willing and able to comply with all study procedures
9. Willing to provide a personally signed and dated informed consent form detailing all pertinent aspects of the trial.

Exclusion Criteria:

1. Suffering from recently diagnosed or unmanaged medical conditions including but not limited to: diabetes, hyper/hypotension, cardiovascular disease, a gastrointestinal disease requiring regular use of medications, gallbladder disease, autoimmune disease, endocrine disease, acute or chronic pain condition, or cancer/malignancy
2. Diagnosis of psychiatric or neurological conditions including but not limited to: psychiatric disorders other than mild-to-moderate depression and/or anxiety disorder, or neurological disease (e.g., Parkinson's, Alzheimer's disease, intracranial hemorrhage, head or brain injury)
3. Regular medication intake, including but not limited to anticholinergics, anti-epileptics, acetylcholinesterase inhibitors, benzodiazepines, antipsychotics, opioids, or corticosteroids.
4. Within 2 months before screening, the use of pharmaceutical medications, including but not limited to immunosuppressant drugs, antibiotics, and steroids
5. Change in medication (dose or type) in the last 3 months or an expectation to change during the study duration. Permitted medications include, but are not limited to, pharmaceutical antidepressants such as selective serotonin reuptake inhibitors (SSRIs), and serotonin and norepinephrine reuptake inhibitors (SNRIs), cholesterol-lowering medications, antihypertensives, proton pump inhibitors, and thyroid medications,
6. Use of probiotics or mood support supplement up to 4 weeks before study commencement
7. Current or 12-month history of illicit drug abuse
8. Alcohol intake greater than 14 standard drinks per week
9. Any significant surgeries over the last year
10. Women who are pregnant, breastfeeding or intend to fall pregnant