English walnuts (Juglans regia L.) protect endogenous antioxidants in humans

Abstract

Ellagic acid monomers, polymeric tannins and related phenolic compounds isolated from English walnuts (Juglans regia L.) have been reported to inhibit LDL oxidation ex vivo and decrease biomarkers of oxidative stress in animal models. To determine whether dietary and endogenous antioxidants are preserved following walnut consumption in humans, we conducted a pilot study in 3 healthy adults. Subjects followed a low polyphenol diet for 2 d prior to the intervention. Fasting blood was then collected at baseline (0 h) and 2 h after consuming a single dose (45 g) of walnuts (WC). Lipophilic free radical initiators were added ex vivo, ±10 μM GAE methanolic walnut extract (WE). The oxidizability of lipid and aqueous plasma components were measured over 4 h and results expressed as percent area under the time course curve. WE protected α‐tocopherol against oxidation at 0 h (P=0.045), but at 2 h the in vitro effect of WE was modest due to a contributing protective action by WC (P=0.021). At 2 h WE protected β‐carotene > WC alone (P=0.039). However, the interactive effect of WC + WE was > WE alone at 0 h (P=0.026). At 2 h, WC + WE also protected lycopene > WE alone at 0 h (P=0.032). No changes in plasma antioxidant levels were observed at 2 h. These data suggest that walnuts may protect against oxidative damage in human plasma by preserving endogenous antioxidant defenses. (Supported by USDA and California Walnut Commission)