Effects of protein isolates from radish and spinach leaves on serum lipids levels in rats.

Radish and spinach leaf protein isolates (RLP and SLP, respectively) were prepared from chilled aqueous 0.2% sodium hydroxide extract of their leaves. The RLP and SLP, and those supplemented with methionine (RLP+Met and SLP+Met, respectively) to become equal to casein in methionine content, were compared with casein for their effects on serum cholesterol level in rats fed with a cholesterol-enriched diet for 14 days. Each protein isolate was incorporated into the cholesterol-enriched diet to provide a 15% protein level. RLP was extremely inferior to SLP and casein for body weight gain of rats, but that of rats fed with RLP+Met diet was almost equal to that of casein and SLP groups. The serum cholesterol level in rats fed with SLP and SLP+Met diets was significantly lower as compared with that of the casein-fed rats. Both the amounts of excreted cholesterol and bile acids were significantly higher in rats fed with the SLP and SLP+Met diets than that of the casein-fed rats. These results suggest that the hypocholesterolemic action of SLP may in part have been due to the inhibition of intestinal absorption of both cholesterol and bile acids. RLP+Met diet tended to decrease the serum cholesterol level as compared to casein diet, but the difference was not significant.