A controlled 72-hour crossover trial involving 18 adults with elevated cardiovascular disease risk revealed that urinary metabolic phenotyping can detect dietary adherence within 24 hours with 96% accuracy. The NICE-compliant diet reduced systolic blood pressure and atherogenic lipids, while a Western-style diet increased these risk markers. Researchers identified 27 discriminatory urinary metabolites that reliably distinguished between dietary patterns. This metabolic fingerprinting approach represents a significant advancement over self-reported dietary assessments, which are notoriously unreliable in free-living populations. The technology could revolutionize clinical nutrition by enabling real-time monitoring of dietary compliance in cardiovascular prevention programs. The rapid metabolic response—detectable within a single day—suggests our bodies adapt to dietary changes far quicker than previously appreciated. However, this preprint study awaits peer review and involved only 18 participants over three days, limiting broader applicability. The controlled inpatient setting, while ensuring dietary compliance, may not reflect real-world eating behaviors. If validated in larger, longer-term studies, this objective biomarker approach could transform personalized nutrition interventions and clinical trial design in cardiovascular medicine.