57 healthy volunteers (23 vegetarians and vegans and 34 omnivores) were recruited. In this study, participants who self-reported not having eaten any meat or seafood products for prior 2 years or longer were defined as vegetarians. All participants were screened using a health history questionnaire. Inclusion criteria were as follows: (1) age ≥ 20 years and (2) no exposure to antibiotics, probiotics, or carnitine supplements within the previous month. Participants were excluded from the study if they reported recent gastrointestinal discomfort (such as abdominal pain or diarrhea) or a history of chronic diseases including myasthenia gravis, diabetes mellitus, chronic renal disease, hyperparathyroidism, epilepsy, and severe anemia. Each participant collected a fecal sample at home by using a stool collection kit and sent the sample to our lab in cold storage within 24 hours of collection. The samples were then aliquoted and stored at −80°C for further examination. Fecal genomic DNA was extracted using the Mobio PowerFecal DNA Isolation Kit according to the manufacturer’s instructions. Two-step polymerase chain reaction (PCR) workflow was performed for library preparation in accordance with procedures described in the Illumina 16S sample preparation guide. The 16S rRNA gene V3-V4 region was amplified and sequenced on the Illumina Miseq platform for paired-end sequencing (2 × 300 bps)