Evidence indicates that the metabolic turnover of food-derived reactive orally absorbed advanced glycation end products (AGEs) or glycotoxins (GTs) is delayed, possibly contributing to the tissue damage induced by endogenous AGEs, especially in patients with diabetes and kidney disease. The aim of this study was to explore whether pharmacologic inhibition of dietary AGE bioreactivity by aminoguanidine (AG) can improve turnover and renal excretion of these substances. Normal Sprague-Dawley rats were fed single-labeled [14C]AGE-ovalbumin, double-labeled [14C-125I]AGE-ovalbumin, or control 125I-labeled ovalbumin diet plus free [14C]glucose, with or without AG (0.2% in water). [14C]AGE- and 125I-labeled peptide-associated radioactivity (RA) were compared with AGE immunoreactivity (by enzyme-linked immunosorbent assay) in tissues, serum, and 72-h urine samples. The effect of AG on dietary AGE bioreactivity was assessed by monitoring the inhibition of covalent complex formation between fibronectin (FN) peptide fragments and serum components, after a meal of labeled dietary AGE with or without AG. The radiolabeled AGE diet produced serum absorption and urinary excretion peaks kinetically distinct from those of free [14C]glucose or [125I]ovalbumin. Some 26% of the orally absorbed AGE-ovalbumin was excreted in the urine, whereas after AG treatment, urinary excre-tion of dietary AGEs increased markedly (to >50% of absorbed). More than 60% of tissue-bound RA was found covalently deposited in kidneys and liver, whereas after treatment with AG, tissue AGE deposits were reduced to <15% of the amount found in untreated AGE-fed controls. Sera enriched for dietary GTs formed covalently linked complexes with FN, a process completely inhibitable by AG cotreatment. Amelioration of dietary GT bioreactivity by AG improves renal elimination and prevents tissue deposition of food GTs. This may afford a novel and potentially protective use of AG against excessive tissue AGE toxicity in diabetic patients with renal disease.