1. Study Background and Purpose Obesity is a complex chronic disease closely linked to comorbidities such as cardiovascular disease, hypertension, and diabetes. With lifestyle changes, obesity prevalence continues to rise. Current treatments focus on weight loss through dietary control and exercise, but weight regain is common due to metabolic adaptations (e.g., post-caloric restriction). Gut microbiota play a critical role in weight management, and probiotics may reduce weight regain by modulating appetite and metabolism. Studies suggest probiotics enhance satiety and reduce appetite. This study aims to evaluate the potential of probiotics in obesity management, specifically their impact on gut microbiota modulation and hormonal regulation to mitigate weight regain. Ethical approval has been obtained from the Peking Union Medical College Hospital Ethics Committee.

2. Study Design

   This 198-participant, randomized, interventional trial will assign subjects to three groups (1:1:1 ratio):

   Placebo group (maltodextrin-based placebo) Probiotic Group 1 Probiotic Group 2 Randomization will be conducted via sealed envelopes (no researcher/participant bias). All groups receive standardized nutritional counseling, caloric restriction plans, and body composition assessments. Probiotics (produced by Shenzhen BaoShiJian Biotechnology Co., Ltd., compliant with standard Q/BSJ 0023S-2024) will be administered orally (2 bottles twice daily) for 84 days .

3. Study Procedure Informed Consent : Required before participation. Screening Phase : Demographic history, medical records, concomitant medications, validated questionnaires, body composition analysis, and blood/urine/stool tests.

   Intervention : Daily probiotic or placebo intake for 84 days. Follow-ups : Visits at Day 42 and Day 85 for adherence checks, anthropometric measurements, and repeat testing.

4. Study Completion Duration : 84 days. Post-Study : Placebo group receives 1-month free probiotic supply; others return to standard care. A 30-day post-study follow-up (phone/WeChat) will assess safety.

   Withdrawal : Participants may exit anytime. Investigators may withdraw participants for safety reasons.

5. Potential Benefits Personalized nutrition counseling and body composition reports. Free clinical evaluations and health coaching. Contribution to novel weight management strategies for weight-cycling populations.

6. Risks and Discomforts Adverse Events : Gastrointestinal symptoms or discomfort. Immediate reporting required for medical management.

Inconveniences :

3 on-site visits (blood/urine/stool tests, anthropometry) with fasting blood draws (~7-20 mL/session).

1 telehealth visit (25 min questionnaire). Daily diary cards. Compensation : 150 RMB travel reimbursement + study-provided scales. 7. Alternative Options

Participants may opt for:

Intermittent fasting. Pharmacotherapy (e.g., GLP-1 agonists). Standard dietary recommendations. 8. New Information Any significant findings during the trial will be communicated to participants, who may choose to continue or withdraw.

9. Costs and Reimbursement No-cost : All investigational products (probiotics/placebo), lab tests, and body composition analyses.

Reimbursement : 150 RMB travel compensation + study tools (body fat scale, food scale, tape measure).

10. Adverse Event Policy All injuries attributed to the intervention will be covered by Shenzhen BaoShiJian Biotechnology Co., Ltd. 's insurance. Legal liability extends beyond insurance coverage.

Inclusion Criteria:

• Obesity : BMI ≥28 kg/m² and <35 kg/m².
• Weight Cycling History :

Documented weight loss attempts within the past 2 years (≥3 episodes) with ≥5% body weight fluctuation.

• Age : 18-60 years (inclusive), male or female.
• Comprehension and Voluntariness : Ability to understand the weight loss protocol and willingness to complete the full study.
• Informed Consent : Signed informed consent form.

Exclusion Criteria:

• Weight-Loss Medications : Current use of medications affecting weight (e.g., orlistat, GLP-1 receptor agonists, metformin).
• Diabetes Mellitus : Diagnosed diabetes or use of antidiabetic medications.
• Severe Metabolic Abnormalities :

Triglycerides >2.5× upper limit of normal (ULN) Cholesterol >2.5× ULN (method-dependent) Fasting whole-blood glucose >11.1 mmol/L Uric acid >2× ULN

• Pregnancy/Lactation : Currently pregnant, breastfeeding, or planning pregnancy within 3 months.
• Severe Organ Dysfunction : Advanced cardiovascular, hepatic, pulmonary, renal, or other critical organic diseases.
• Thyroid Disorders : Diagnosed hyperthyroidism or hypothyroidism.
• Gastrointestinal Diseases : History of acute/chronic or active gastrointestinal disorders.
• Antibiotic Use : Oral/intravenous antibiotics within the past month.
• Psychiatric Disorders : Severe mental illness requiring routine psychiatric medication.
• Secondary Obesity : Hypothalamic obesity, Cushing's syndrome, hypogonadism-related obesity, etc.
• Specific Diets : Long-term vegan or restrictive dietary patterns.
• Weight Instability : ≥10% body weight change within the past 3 months.
• Compliance Concerns : Poor compliance or inability to adhere to the weight loss protocol (as judged by the investigator).