The effects of walnuts on cardiovascular disease risk have been studied; however, the contribution of individual walnut components has not been assessed.
This study evaluated the acute consumption of whole walnuts (85 g), separated nut skins (5.6 g), defatted nutmeat (34 g), and nut oil (51 g) on postprandial lipemia, endothelial function, and oxidative stress. Cholesterol efflux (ex vivo) was assessed in the whole walnut treatment only. A randomized, 4-period, crossover trial was conducted in healthy overweight and obese adults (n = 15) with moderate hypercholesterolemia. There was a treatment by time point interaction for TG (P < 0.01), and increased postprandial levels were observed for the oil and whole walnut treatments (P < 0.01). Walnut skins decreased the reactive hyperemia index (RHI) versus baseline (P = 0.02), such that a difference persisted between the skin and oil treatments (P = 0.01). The Framingham RHI (fRHI) was maintained with the oil treatment compared to the skins and whole nut (P < 0.05). There was a treatment effect for the ferric reducing antioxidant potential (FRAP) (P < 0.01), and mean FRAP was greater with the oil and skin treatments compared to nutmeat (P < 0.01).
Cholesterol efflux was increased by 3.3% following whole walnut consumption in J774 cells cultured with postprandial serum compared to fasting baseline (P = 0.02). Walnut oil favorably affected endothelial function, and whole walnuts increased cholesterol efflux. These two novel mechanisms may explain, in part, the cardiovascular benefits of walnuts.