Trimethylamine N-oxide (TMAO) was recently discovered as a novel and independent risk factor for promoting atherosclerosis while it is generated from dietary carnitine through the metabolism of gut microbiota for decades. Allicin, the major compound in raw garlic juice, is a naturally antimicrobial phytochemical found in raw garlic juice and easily acquired from the diet. Investigators' previous study suggests dietary allicin reduces the transformation of L-carnitine to TMAO through the impact on gut microbiota in mice. Therefore, it is worth investigating whether raw garlic juice intake could reduce the TMAO productivity of human gut microbiota as well as modulate gut microflora. Investigators plan to recruit 10 TMAO producers to receive garlic juice for one week. The plasma and urine TMAO concentration will be measured by the LC-MS, and the gut microbiota composition will be analyzed by the next-generation sequencing, through bioinformatics analysis. Investigators expected after intake garlic juice for one week, it could prevent the cardiovascular disease risk via gut microbiota modulation and reduction of plasma and urine TMAO.~Screening of the TMAO producer:~The healthy participants were recruited, the criteria as follows: (1) age ≥ 20 years old; (2) no exposure to antibiotics, probiotics, or carnitine supplements within the previous month; (3) have no history of chronic diseases including, diabetes mellitus, myasthenia gravis, chronic renal disease, hyperparathyroidism, epilepsy, and severe anemia; (4) Participants were excluded from the study if they reported recent gastrointestinal discomfort (such as abdominal pain or diarrhea). To screening the TMAO producer, Investigators use the oral carnitine challenge test (OCCT) method which previously exhibited better efficacy than fasting plasma TMAO to identify the TMAO producer phenotype. All of the participants fasted at least 8 hours before performing OCCT. 1500 mg of L-carnitine (3 tablets, General Nutrition Centers, Inc., USA) orally administrated to the participants. The blood and urine of participants were collected at 0, 24, 48, and 72 hours after carnitine intake. Participants with plasma TMAO ≧ 10 μM after OCCT were defined as high TMAO producers and proceeded into the garlic juice intervention test.~Garlic Juice Intervention:~High-TMAO producers asked to consume 55 mL of raw garlic juice (48 mg of allicin equivalent) once a day during dinner for one week. High-TMAO producers suggested consuming the garlic juice with a meal. The high-TMAO producers were free to choose their diet, no restriction on the type of food. After one week of raw garlic juice intervention, the second OCCT was performed.
Investigators recruited 10 trimethylamine N-oxide (TMAO) producers to test the effect of garlic juice containing allicin on gut microbiota modulation and TMAO production.