Scientific Study

BACKGROUND. In a recent six-year follow-up study; we found that frequent consumption of nuts was associated with a reduced risk of ischemic heart disease. To explore possible explanations for this finding; we studied the effects of nut consumption on serum lipids and blood pressure. METHODS. We randomly placed 18 healthy men on two mixed natural diets; each diet to be followed for four weeks. Both diets conformed to the National Cholesterol Education Program Step 1 diet and contained identical foods and macronutrients; except that 20 percent of the calories of one diet (the walnut diet) were derived from walnuts (offset by lesser amounts of fatty foods; meat; and visible fat [oils; margarine; and butter]). RESULTS. With the reference diet; the mean (+/- SD) serum values for total; low-density lipoprotein (LDL); and high-density lipoprotein (HDL) cholesterol were; respectively; 182 +/- 23; 112 +/- 16; and 47 +/- 11 mg per deciliter (4.71 +/- 0.59; 2.90 +/- 0.41; and 1.22 +/- 0.28 mmol per liter). With the walnut diet; the mean total cholesterol level was 22.4 mg per deciliter (0.58 mmol per liter) lower than the mean level with the reference diet (95 percent confidence interval; 28 to 17 mg per deciliter [0.72 to 0.44 mmol per liter]); the LDL and HDL cholesterol levels were; respectively; 18.2 mg per deciliter (0.47 mmol per liter) (P < 0.001) and 2.3 mg per deciliter (0.06 mmol per liter) (P = 0.01) lower. These lower values represented reductions of 12.4; 16.3; and 4.9 percent in the levels of total; LDL; and HDL cholesterol; respectively. The ratio of LDL cholesterol to HDL cholesterol was also lowered (P < 0.001) by the walnut diet. Mean blood-pressure values did not change during either dietary period. CONCLUSIONS. Incorporating moderate quantities of walnuts into the recommended cholesterol-lowering diet while maintaining the intake of total dietary fat and calories decreases serum levels of total cholesterol and favorably modifies the lipoprotein profile in normal men. The long-term effects of walnut consumption and the extension of this finding to other population groups deserve further study.