Japanese plums are typically rich in anthocyanins, a class of flavonoid pigments known for their vibrant coloration and potential health benefits. The Queen Garnet Plum (QGP), a Japanese blood plum cultivar developed through a Queensland Government breeding program, was specifically selected for its high anthocyanin content and used as a test food to investigate the in vivo metabolism and biotransformation of anthocyanins. Ethical approval for the study was granted by The University of Queensland Medical Research Ethics Committee (approval code: 2012000182). Ten healthy, non-smoking male volunteers (aged 18–35 years; mean BMI: 22.9 ± 3.2 kg/m²) were recruited. Participants maintained their usual diet but abstained from polyphenol- and ascorbic acid-rich foods and beverages for 48 hours prior to treatment. Alcohol and all medications, including over-the-counter drugs, were avoided throughout the study period. In a randomized crossover design, subjects received a single dose of either QGP juice (containing 0.95 mmol anthocyanins) or water. After a two-week washout period, the intervention was repeated with the alternative treatment. On each test day, following an overnight fast, participants consumed 400 mL of the assigned beverage along with white bread rolls at 9:00 a.m. During the 24-hour experimental period, only water and three standardized meals were permitted. Urine samples were collected in two intervals (0–4 h and 4–24 h post-dose) and stored at –80°C after stabilization. Analysis by LC-ESI-MS revealed that 25% of total anthocyanins were excreted as intact glycosides (cyanidin-3-glucoside and cyanidin-3-rutinoside), while 75% were excreted as methylated and glucuronidated metabolites. Notably, peonidin derivatives—methylated forms of cyanidin—were the predominant metabolites. These compounds have been associated with anti-inflammatory, neuroprotective, and vascular-supporting effects. Additionally, the mean urinary excretion of hippuric acid increased by 3.38 mmol/24 h following QGP juice consumption—a 4.5-fold increase compared to the control. Hippuric acid is commonly used as a biomarker for polyphenol intake and is also linked to gut microbial activity, suggesting potential relevance to gut health and microbial diversity. Emerging evidence also points to possible neuroprotective properties of hippuric acid, although further research is needed. Given that hippuric acid concentrations in 24-hour urine samples were in the millimolar range, while conjugated anthocyanin metabolites (including peonidin derivatives) were present in the nanomolar range, it is plausible that low-molecular-weight metabolites like hippuric acid contribute more significantly to the observed health effects of anthocyanin-rich foods.