Clinical Briefs
With Comments from John La Puma, MD, FACP
Walnuts for Reducing Cholesterol Levels
November 2000; Volume 3; 131
Source: Zambón D, et al. Substituting walnuts for monounsaturated fat improves the serum lipid profile of hypercholesterolemic men and women. A randomized crossover trial. Ann Intern Med 2000;132:538-546.
It has been reported that walnuts reduce serum cholesterol levels in normal young men. To assess the acceptability of walnuts and their effects on serum lipid levels and low-density lipoprotein (LDL) oxidizability in free-living hypercholesterolemic persons, we designed a randomized, crossover feeding trial. We studied 55 men and women (mean age, 56 years) with polygenic hypercholesterolemia at a university hospital’s lipid clinic. We gave them a cholesterol-lowering Mediterranean diet and a diet of similar energy and fat content in which walnuts replaced approximately 35% of the energy obtained from monounsaturated fat. Patients followed each diet for six weeks.
Forty-nine persons completed the trial. The walnut diet was well tolerated. Planned and observed diets were closely matched. Compared with the Mediterranean diet, the walnut diet produced mean changes of -4.1% in total cholesterol level, -5.9% in LDL cholesterol level, and -6.2% in lipoprotein(a) level. The mean differences in the changes in serum lipid levels were -0.28 mmol/L (95% confidence interval [CI], -0.43 to
-0.12 mmol/L) (-10.8 mg/dL [-16.8 to
-4.8 mg/dL]) (P < 0.001) for total cholesterol level, -0.29 mmol/L (CI, -0.41 to -0.15 mmol/L) (-11.2 mg/dL [-16.3 to -6.1 mg/dL]) (P < 0.001) for LDL cholesterol level, and -0.021 g/L (CI, -0.042 to -0.001 g/L) (P = 0.042) for lipoprotein(a) level. Lipid changes were similar in men and women except for lipoprotein(a) levels, which decreased only in men. LDL particles were enriched with polyunsaturated fatty acids from walnuts, but their resistance to oxidation was preserved.
We find that substituting walnuts for part of the monounsaturated fat in a cholesterol-lowering Mediterranean diet further reduced total and LDL cholesterol levels in men and women with hypercholesterolemia.
COMMENT
The Mediterranean diet has much to recommend it—flavor, familiarity, fun, good fats. The whole traditional Mediterranean diet, however, which derives 40-45% of its calories from fat, especially olive oil, is not a tenable American option. Affluent and eager as we are, most of us simply would add olives and olive oil, fish, and nuts to our currently over-the-top caloric intakes. And because the average American adult already eats 216 calories/d more than he or she did 25 years ago, that would be too much.
But components of the traditional Mediterranean diet (fish, green vegetables, very little red meat, and eggs) are individually deserving of special attention, and scientists are trying hard to find the magic bullet in food. Gratefully, these investigators gave whole walnuts (untoasted, but they were practicing science, not cooking), and substituted them for the monounsaturates (i.e., olive oil) in the Mediterranean diet.
Average LDLs dropped from 196 mg/dL to 174 mg/dL on walnuts vs. 185 mg/dL on the control diet.
It’s no surprise that polyunsaturated walnut fat is better than butter, cream, cheese, and beef. But to substitute walnuts’ polyunsaturated omega-3 fats for monounsaturated ones, and to lower cholesterol with whole foods, other than fresh garlic—that’s new! That’s exciting! And to get to eat more nuts—that’s good too!
But not too many more—14 walnut halves, or fewer if they’re large, and you’re up to an ounce. An ounce is a serving, and packs 180 calories—the same as 4 teaspoons of olive oil. In this study, people ate 8-11 walnuts daily, and remained in statin territory. But eating nuts is a start, and it is something that patients can do that is positive and helpful.
Could other nuts do this? Yes, probably. Pecans have been studied recently; 3/4 cup, which have more monounsaturates than polys, lowered LDLs by 6% over eight weeks. Whether the mechanism is antioxidant-related is unknown. But the effect seems to be independent of simply limiting saturated fat.
Recommendation
Nuts are good medicine. Toast em if you got em. Then eat an ounce at a time and skip the olive oil that day.
November 2000; Volume 3; 131
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