Design: Experimental study with a randomized design.

Subjects: Twenty healthy women and 20 healthy men.

Interventions: Subjects were randomly assigned to consume each of two mixed natural diets for 4 weeks in a cross-over design. Reference and walnut diets were designed and the walnut diet had 12.5% of the energy derived from walnuts (44-58g/day).

Results: The total cholesterol and serum apolipoprotein B concentrations, and the ratio of LDL cholesterol to HDL cholesterol was significantly lowered in women and men when fed on the walnut diet, than when on the reference diet (P less than or equal to 0.05). The LDL cholesterol concentration was significantly lowered in women on the walnut diet (0.22 mmol/l, P = 0.0008), whereas this decrease was not significant in men (0.18 mmol/l, P = 0.078). The most prominent change in the fatty acid composition of the cholesteryl esters from serum after the walnut diet was an elevation of alpha-linolenic acid in women (76%, P < 0.001) and men (1107%, P < 0.001). This elevation was negatively correlated to the change in LDL cholesterol in women (r = 0.496, P = 0.019) and men (r = 0.326, P = 0.138). The LDL oxiclizability in women was not influenced by the diets (P = 0.19).

Conclusions: alpha-linolenic acid in the walnut diet appears to be responsible for the lowering of LDL cholesterol in women.

Sponsorship: Kyushu University (Fukuoka, Japan) and the California Walnut Commission (California, USA).