Blood carotenoids offer the clearest signal of fruit and vegetable eating habits

The review finds that several candidate biomarkers may help estimate fruit and vegetable intake more objectively than self-reported dietary tools, but most remain limited by specificity, sampling burden, supplement use, or incomplete validation. Blood and skin carotenoids appear strongest for habitual intake, while vitamin C, folate, urinary flavonoids, hippuric acid, and potassium may be more useful for short-term intake or intervention adherence.