A Chemically Defined Diet With Insufficient Sulfur Amino Acids Induces Oxidation of Plasma Cysteine/Cystine and Glutathione/Glutathione Disulfide Redox State in Humans

Sulfur amino acid (SAA) availability is critical for glutathione (GSH) synthesis. GSH has an important role in detoxification and maintenance of intracellular glutathione/glutathione disulfide (GSH/GSSG) redox as well as extracellular cysteine/cystine (Cys/CySS) redox in vitro . Intermittent periods of SAA insufficiency are common due to food selection, dieting, and fasting. To examine the effects of dietary SAA insufficiency on redox status in vivo , young, healthy volunteers were studied on 2 separate occasions for 60 hours in the General Clinical Research Center (GCRC) at Emory University Hospital. During each study period, volunteers consumed 1 of 2 chemically defined diets modified for SAA content (100% or 0% of the Recommended Dietary Allowance for SAA intake) for 3 days. Blood was drawn hourly for 12 hours on day 3. Results from 4 individuals show that consumption of the 0% SAA diet resulted in a significant oxidation (~ 9 mV) of plasma Cys/CySS redox status as compared to consumption of the 100% SAA diet (−73± 0.8 mV vs. −82± 0.8 mV respectively). In contrast, consumption of the 0% SAA diet did not affect plasma GSH/GSSG redox status as compared to control diet (−123± 2 mV vs. −124.3± 1 mV respectively). We conclude that 3‐day consumption of a diet insufficient in SAA induces significant oxidation of the plasma Cys/CySS redox state while having no affect on plasma GSH/GSSG redox status in humans. Support: NIEHS RO1 09047.