Gut bacteria may hold key to stronger muscles in aging

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Men or women aged 50 to under 80 years * Meeting the 2025 Asian Working Group for Sarcopenia (AWGS) criteria for sarcopenia (low muscle mass and low handgrip strength) or possible sarcopenia (low muscle mass with either low handgrip strength or low physical performance). Low muscle mass is defined as ASM/height\^2 measured by bioelectrical impedance analysis below 7.6 kg/m\^2 for men and below 5.7 kg/m\^2 for women aged 50 to 64 years, and below 7.0 kg/m\^2 for men and below 5.7 kg/m\^2 for women aged 65 years or older. Low handgrip strength is defined as the maximum value of the dominant hand at or below the following thresholds: 34.5 kg for men and 22.0 kg for women aged 50 to 54 years; 33.5 kg for men and 21.5 kg for women aged 55 to 59 years; 31.0 kg for men and 20.0 kg for women aged 60 to 64 years; 29.0 kg for men and 19.0 kg for women aged 65 to 69 years; 27.5 kg for men and 18.0 kg for women aged 70 to 74 years; 26.0 kg for men and 16.8 kg for women aged 75 to 79 years. Low physical performance is defined as more than 10 seconds on the 5-time chair stand test of the Short Physical Performance Battery for participants aged 50 to 64 years, and more than 12 seconds for those aged 65 years or older. * Not having participated in a commercial exercise program or performed regular resistance exercise 2 or more times per week within the 3 months before study participation * Physically able to participate in the standardized resistance exercise program provided from the start of the study at least 3 times per week, and willing to comply with it * Having received a full explanation of the purpose and procedures of the study and having voluntarily provided written informed consent Exclusion Criteria: * Short Physical Performance Battery total score of 3 or less * Cachexia or unintentional weight loss of 5 percent or more within the past 3 months * History of fracture or musculoskeletal surgery within the past 6 months * Musculoskeletal or functional limitation that precludes isokinetic strength testing or performance of the standardized exercise program (for example, severe osteoarthritis or rheumatoid arthritis) * Uncontrolled or clinically unstable endocrine disease (for example, Cushing syndrome or adrenal insufficiency) * Severe respiratory disease (COPD GOLD stage III to IV or long-term oxygen therapy) * Uncontrolled hypertension (systolic blood pressure 160 mmHg or higher, or diastolic blood pressure 100 mmHg or higher), uncontrolled diabetes mellitus (fasting glucose 160 mg/dL or higher), or uncontrolled thyroid disease * Major cardiovascular or cerebrovascular event within the past 6 months (acute myocardial infarction, stroke, unstable angina, percutaneous coronary intervention, or coronary artery bypass grafting) * History of malignancy within 3 years before screening or currently receiving anticancer treatment, except malignancies with negligible risk of metastasis or death such as adequately treated non-melanoma skin cancer or carcinoma in situ * AST or ALT greater than 3 times the upper limit of normal at screening * Serum creatinine greater than 2 times the upper limit of normal at screening * History of gastrointestinal surgery or gastrointestinal disease that may affect absorption of the study food, except simple appendectomy or hernia repair * Known hypersensitivity to the active ingredient or any component of the study food * Use of systemic antibiotics or bowel preparation agents within 2 weeks before screening * Intake of probiotics, prebiotics, or lactic acid bacteria or fermented milk products 4 or more times per week within 2 weeks before screening, excluding fermented foods included in a regular diet * Continuous use of protein supplements or muscle-related health functional foods within 1 month before screening * Use of medications that may affect muscle mass or muscle strength within 3 months before screening, including systemic corticosteroids (oral or injectable), testosterone, growth hormone preparations, selective androgen receptor modulators, and anti-obesity drugs * Severe alcohol use disorder according to DSM-5 diagnostic criteria * Continuous use of psychiatric medication for schizophrenia, bipolar disorder, or severe major depressive disorder, excluding intermittent medication for sleep disturbance * Participation in another clinical trial within 3 months before screening, or current participation in another clinical trial * Women who are pregnant, breastfeeding, or planning to become pregnant during the study period * Any other condition that, in the judgment of the principal investigator, may affect the safety of the participant or the integrity of the study results