The purpose of this study is to investigate the effects of a probiotic blend on qualitative (subjective interviews and self-reporting) and quantitative (changes in brain activity, heart rate, cortisol, and reactivity) measures of stress in healthy undergraduate students.

There is a burgeoning literature involving nonhuman animal and human studies linking the microbiota environment in the gut to brain-behaviour relations. For example, animal studies demonstrate that germ-free rodents show heightened HPA-axis responses to stress compared to gnotobiotic animals. There are also a number of nonhuman and human studies that show positive effects of reducing stress after being treated with different probiotics. For example, in one recent double blind study in humans using standardized questionnaires indicated a greater reduction of stress and anxiety symptoms after one month of supplementation with a probiotic formulation compared to placebo. The groups were also differentiated by urinary cortisol levels after treatment. Other studies have found positive effects of probiotic treatment and stress reduction using other probiotics. Accordingly, there is accumulating empirical evidence from animal and human studies of the positive effects of probiotic treatment on stress reduction.

In this study, the investigators will investigate the stress reduction effects of the Lallemand Health Solutions (LHS) Probio'Stick® on healthy undergraduate students. The study will be conducted at the McMaster LIVELab, which is capable of collecting both physiological and behavioural measures from groups of up to 100 participants at a time.

Registration into this clinical trial will require students be screened via McMaster's SONA system (mcmaster.sona-systems.com). After the screening, participants that are eligible to participate will be given the option to register for an information meeting at which point one may opt to enrol in the study or not.

Once in the study, participants will undergo an initial screening in the LIVELab where they will be exposed to auditory, visual, and performance based stressors to measure a baseline. After such point, they will be randomized to receive Probio'Stick® or placebo for a 6-week, once daily, probiotic treatment at home. Following the 6 week intervention, participants will return to the lab for a second testing using the same procedures to establish a change from baseline.

Inclusion Criteria:

• Answering "Yes" to questions 3, 8 and 9 of the Cohen's Perceived Stress Scale.
• Willingness to complete questionnaires, records, and diaries associated with the study and to complete all site visits.
• Willingness to discontinue consumption of fermented foods or probiotics (e.g. yogurts, with live, active cultures, or supplements).
• Ability to provide informed consent.

Exclusion Criteria:

• Must not be currently taking another probiotic regiment or another investigational product within 3 months of the screening visit.
• Must not currently be taking medications for depression or anxiety, including benzodiazepines, SSRIs, or antipsychotics or receiving counselling for depression or anxiety.
• Must not be immune-compromised or immuno-suppressed (e.g. AIDS, lymphoma, participants undergoing long-term corticosteroid treatment, chemotherapy and allograft participants).
• Must not have experienced bloody diarrhea in the past month prior to beginning the study.
• Must not have undergone any surgery within the three months prior to beginning the study, particularly surgeries involving the colon.
• Must not have any soy or milk allergy.
• Must not be pregnant or breast-feeding or planning on becoming pregnant.
• Must not have used of any antibiotic drug (e.g., neomycin, rifaximin) within 1 month of screening.