Evaluate the effectiveness and safety of Lactobacillus delbrueckii subsp. bulgaricus LB42 as a food supplement compared to a placebo in improving intestinal and immune functions in healthy adults.

Inclusion Criteria:

1. Age 18-45 years
2. Willing to undergo 3 follow-up visits during the intervention period
3. Willing to provide 2 blood, urine, and stool samples during the intervention period
4. Willing to self-administer one of the probiotics/placebo once daily during the intervention period
5. Good eyesight, able to read and write, and can wear glasses
6. Have good hearing and be able to hear and understand all instructions during the intervention

Exclusion Criteria:

1. Suffering from digestive disorders, mainly gastrointestinal disorders (celiac disease, ulcerative colitis, Crohn's disease)
2. Has a severe neurological condition (epilepsy, stroke, severe head trauma, meningitis within the past 10 years, brain surgery, brain tumor, prolonged coma - excluding general anesthesia)
3. Has received/is receiving treatment for the following psychiatric disorders: alcohol/drug/substance abuse dependence, schizophrenia, psychosis, bipolar disorder
4. Take medication for depression or low mood
5. Suffering from internal organ failure (heart, liver, or kidney failure, etc.)
6. Radiotherapy or chemotherapy in the past
7. Surgery/procedure under general anesthesia within the past three years, or planned to undergo a procedure/procedure under general anesthesia within the next 3 months during this trial
8. Have had hepatitis (hepatitis B, hepatitis C), HIV or syphilis in the past