Probiotics Improve Constipation

• Probitics (Dietary supplement): The intervention period of this study will last for 8 weeks (56 days), during which each participant will attend three study visits scheduled at baseline (Week 0), Week 1, Week 2, Week 4, and Week 8.
• Placebo (Dietary supplement): The intervention period of this study will last for 8 weeks (56 days), during which each participant will attend three study visits scheduled at baseline (Week 0), Week 1, Week 2, Week 4, and Week 8.

Primary outcomes

• Improvement of constipation symptoms [Baseline, Week 1, Week 2, Week 4, Week 8]: Improvement in constipation was assessed using the Bristol Stool Characteristics Scale (BSFS), primarily observing the shift in stool type from type 1-2 (hard stool/constipation) to type 3-4 (normal/ideal soft stool).
• Change in Spontaneous Bowel Movement (SBM) Frequency [Baseline, Week 1, Week 2, Week 4, Week 8]: Change from baseline in number of spontaneous bowel movements. Spontaneous bowel movements are defined as bowel movements occurring without the use of laxatives, enemas, or suppositories within the previous 24 hours.

Secondary outcomes

• Change in Gastrointestinal Symptom Rating Scale (GSRS) Score [Baseline, Week 1, Week 2, Week 4, Week 8]: Change from baseline in GSRS total and subscale scores. GSRS is a 15-item questionnaire assessing gastrointestinal symptoms across 5 domains (reflux, abdominal pain, indigestion, diarrhea, constipation), each rated on a 7-point Likert scale. Higher scores indicate more severe symptoms.
• Change in Patient Assessment of Constipation Symptoms (PAC-SYM) Score [Baseline, Week 1, Week 2, Week 4, Week 8]: Change from baseline in PAC-SYM total score. PAC-SYM is a 12-item questionnaire assessing constipation-related symptoms across 3 subscales (abdominal, rectal, stool), each rated on a 5-point Likert scale. Higher scores indicate more severe symptoms.
• Change in Patient Assessment of Constipation Quality of Life (PAC-QOL) Score [Baseline, Week 1, Week 2, Week 4, Week 8]: Change from baseline in PAC-QOL total score. PAC-QOL is a 28-item questionnaire assessing quality of life related to constipation across 4 domains (physical discomfort, psychosocial discomfort, worries/concerns, satisfaction), each rated on a 5-point Likert scale. Higher scores indicate poorer quality of life.
• Change in Depression, Anxiety, and Stress Scale-21 (DASS-21) Score [Baseline, Week 1, Week 2, Week 4, Week 8]: Change from baseline in DASS-21 total and subscale scores. DASS-21 is a 21-item questionnaire assessing depression, anxiety, and stress across 3 domains, each rated on a 4-point Likert scale. Higher scores indicate more severe psychological distress.
• Change in Serum Inflammatory and Immune Markers [Baseline, Week 8]: Change from baseline in serum levels of interleukin-2 (IL-2), interleukin-4 (IL-4), interleukin-6 (IL-6), interleukin-10 (IL-10), tumor necrosis factor-alpha (TNF-α), and interferon-gamma (IFN-γ).
• Change in Serum Gut-Brain Axis Regulatory Markers [Baseline, Week 8]: Change from baseline in serum levels of 5-hydroxytryptamine (5-HT), motilin (MTL), and substance P (SP).
• Change in Serum Intestinal Barrier Function Markers [Baseline, Week 8]: Change from baseline in serum levels of occludin, zonula occludens-1 (ZO-1), and lipopolysaccharide (LPS).
• Change in Serum Digestive Enzyme Levels [Baseline, Week 8]: Change from baseline in serum levels of pepsin, trypsin, and lipase.
• Change in Gut Microbiota Composition [Baseline, Week 8]: Change from baseline in gut microbiota diversity (alpha and beta diversity) and taxonomic composition at phylum and genus levels, assessed by 16S rRNA sequencing of fecal samples.

Sex: All, ages: 18 Years to 65 Years, accepts healthy volunteers

Inclusion Criteria:

* Aged 18 to 65 years (inclusive).
* Diagnosed with constipation, defined as fewer than 3 spontaneous bowel movements per week and/or Bristol Stool Form Scale types 1 or 2.
* Willing and able to comply with the study protocol and complete all required assessments.
* Provide written informed consent prior to any study-related procedures.
* Male and female participants of childbearing potential must agree to use effective contraception voluntarily from 14 days prior to screening until 6 months after the end of the trial. Female participants of non-childbearing potential (e.g., post-menopausal or surgically sterile) are exempt from this requirement.

Exclusion Criteria:

* Use of products with functions similar to the investigational product within a short period prior to screening that may interfere with the evaluation of study outcomes.
* Intention to change dietary habits significantly during the study period.
* Severe allergies or immunodeficiency.
* Women who are pregnant, breastfeeding, or planning to become pregnant during the trial.
* Severe diseases of vital organs (including cardiovascular, pulmonary, hepatic, or renal disease), metabolic diseases (e.g., diabetes, thyroid disorders), malignancy, or severe immune system disorders.
* Use of antibiotics within the past 30 days.
* Severe psychological or psychiatric disorders.
* Poor compliance (e.g., failure to take the test product as instructed or failure to attend scheduled follow-up visits) that would preclude a valid assessment of efficacy.
* Organic constipation (e.g., caused by structural or pathological conditions).
* Irritable bowel syndrome with constipation (IBS-C).
* History of surgical procedures within 30 days prior to screening that may have caused or contributed to constipation symptoms.
* Intake of probiotic or prebiotic supplements within one month prior to the start of the study.
* Any other condition that, in the investigator's opinion, would make the participant unsuitable for participation in the study.