Development of a Method for <i>in vivo</i> Direct Monitoring of Stored Fat Burning Using Stable Isotope-labeled Fatty Acids

We developed a novel approach for direct and rapid evaluation of the fat-burning effects of various food ingredients in vivo. Male ICR mice were fed a diet containing stable isotope-labeled palmitic acid, and fat oxidation was quantified by measuring the production of labeled carbon dioxide (¹³CO₂) generated during β-oxidation. By evaluating the 24-h fat burning profile, we demonstrated the immediate fat-burning effect of caffeine and the gradual fat-burning effect of curcumin. This methodology allows fat-burning-specific detection rather than fat absorption inhibition, thereby providing a powerful tool for comparing fat-burning effects of different food components in vivo.