Correspondence
Walnuts and Serum Lipids
N Engl J Med 1993; 329:358-360July 29, 1993
- Article
To the Editor:
The report by Sabate et al. (March 4 issue)1 describing a reduction of serum cholesterol levels in normal men after they consumed walnuts has a simple explanation. Three ounces of nuts will supply about 400 kcal daily. The subjects must have reduced their intake of other foods in order to maintain a constant weight. Thus, the energy from nuts would have displaced the energy from other foods containing trans fatty acids. Because of the ubiquity of partially hydrogenated fat additives in food, the average intake of trans fatty acids by Americans is now about 12.5 percent of their total fat intake but ranges widely2. Trans fatty acids have repeatedly been shown to cause hypercholesterolemia3. They may be the main cause of our epidemic of cardiovascular disease, which began in the 1920s, shortly after hydrogenated fat was introduced. This can also explain the “French paradox”: there is less coronary disease in France despite a higher intake of fat there than in the United States, although a lower intake of hydrogenated fat4. This “displacement” hypothesis will also explain the lower levels of coronary disease in Mediterranean countries as compared with countries in Northern Europe. People in the former region use mainly vegetable oils in their food, whereas those in the latter region use margarine.
4 ReferencesGeorge V. Mann, Sc.D., M.D.
3710 Westbrook Ave., Nashville, TN 372051
Sabate J ,Fraser GE ,Burke K ,Knutsen SF ,Bennett H ,Lindsted KD . Effects of walnuts on serum lipid levels and blood pressure in normal men. N Engl J Med 1993;328:603-607
Full Text | Web of Science | Medline2
Enig M ,Atal S ,Keeney M ,Sampugna J . Isomeric trans fatty acids in the U.S. diet. J Am Coll Nutr 1990;9:471-486
Web of Science | Medline3
Mensink RP ,Katan MB . Effect of dietary trans fatty acids on high-density and low-density lipoprotein cholesterol levels in healthy subjects. N Engl J Med 1990;323:439-445
Full Text | Web of Science | Medline4
Renaud S. The “French paradox”: application to the dietary prevention of coronary heart disease. Presented at the Fifth International Congress on Stress, Montreux, Switzerland, February 14-19, 1993. abstract.
To the Editor:
Nut sellers will use the article by Sabate et al., whose study was funded by the California Walnut Commission, to make the ridiculous claim that eating nuts prevents heart attacks.
This article does not show that eating walnuts lowers blood cholesterol levels. It shows that adding walnuts, which are loaded with fat, to a diet and keeping the fat and caloric intake constant will force a vegetarian to restrict the intake of eggs, dairy products, and visible oils, thus reducing the intake of saturated fats and cholesterol, the two dietary components that, when taken with excess calories, raise blood cholesterol levels the most.
In a previous study,1 the authors reported that vegetarians who frequently ate nuts had a reduced risk of ischemic heart disease. I interpret that study as showing that vegetarians who eat nuts are less likely to eat dairy products and eggs. Vegetarians are not supposed to eat meat, so they meet their need for protein by eating dairy products, eggs, nuts, and beans. Vegetarians who restrict their intake of dairy products and eggs have to get their protein from nuts and beans, both of which are very low in saturated fat and devoid of cholesterol.
1 ReferencesGabe Mirkin, M.D.
9900 Georgia Ave., Silver Spring, MD 209021
Fraser GE ,Sabate J ,Beeson WL ,Strahan TM . A possible protective effect of nut consumption on risk of coronary heart disease: the Adventist Health Study. Arch Intern Med 1992;152:1416-1424
CrossRef | Web of Science | Medline
To the Editor:
Sabate et al. suggest that increasing the current per capita consumption of walnuts from 4 g per week to 28 g per day would confer a cardioprotective benefit by lowering the serum level of low-density lipoprotein (LDL) cholesterol. There are two other plausible explanations for the cardioprotective benefits of nuts. First, almonds, pistachios, pecans, and walnuts (but not cashews or peanuts) contain 6 to 10 percent (by weight) n-3 polyunsaturated fat (alpha-linolenic acid). In humans, alpha-linolenic acid (C18:3 n-3) undergoes slow prolongation and desaturation, producing longer-chain n-3 fatty acids (C20:5 n-3 and C22:5 n-3). In both plasma and membrane phospholipids, especially in platelets and endothelial cells, longer-chain n-3 polyunsaturated fatty acids competitively displace arachidonic acid, reducing the ratio of arachidonic acid to n-3 polyunsaturated fatty acids. This shift to a higher concentration of n-3 polyunsaturated fatty acids has a host of cardioprotective benefits, including a substantial modification of the aggregatory, vasoactive, and thrombogenic potential of platelets. Second, since the uptake of oxidized LDL by specific receptors on macrophages is very avid and is not down-regulated by internal macrophage cholesterol content, it leads to the accumulation of lipid-laden foam cells within the arterial wall. Higher plasma levels of n-3 polyunsaturated fatty acids and monounsaturates (provided by these nuts) reduce the oxidation and hence the atherogenicity of LDL cholesterol1,2.
2 ReferencesMichael Mogadam, M.D.
4660 Kenmore Ave., Alexandria, VA 223041
Fisher M ,Levine PH ,Weiner BH , et al. Dietary n-3 fatty acid supplementation reduces superoxide production and chemiluminescence in a monocyte-enriched preparation of leukocytes. Am J Clin Nutr 1990;51:804-808
Web of Science | Medline2
Reaven P ,Parthasarathy S ,Grasse BJ , et al. Feasibility of using an oleate-rich diet to reduce the susceptibility of low-density lipoprotein to oxidative modification in humans. Am J Clin Nutr 1991;54:701-706
Web of Science | Medline
To the Editor:
Sabate et al. recently reported that eating walnuts lowers blood cholesterol levels, a finding consistent with the inverse association between nut intake and mortality due to coronary heart disease in Seventh-Day Adventists1. We studied whether nut intake had a similar association with mortality due to coronary heart disease in a population-based study of 41,837 older women, the Iowa Women's Health Study2. Women 55 to 69 years old, 98 percent of whom were white, completed a food-frequency questionnaire3 in 1986 that asked about the frequency of intake of nuts (serving size of one small packet, or 1 oz). Forty-one percent of the women reported that they never ate nuts; 35 percent, that they ate them one to three times a month; 15 percent, that they ate them about once a week; and 9 percent, that they ate them more often. Over a five-year period, 154 of 34,484 women who had been free of coronary heart disease at base line subsequently died of coronary disease. Coronary mortality was inversely associated with nut intake in these women, an association consistent with the results of the Adventist study (Table 1Table 1
Adjusted Relative Risk of Death from Coronary Heart Disease, According to Level of Nut Intake.)1.Further research is needed to ensure that these findings are due to the effect of eating nuts rather than to other characteristics of the nut eaters. The lipid-lowering effect of walnuts demonstrated by Sabate et al. provides a plausible physiologic mechanism, however.
3 ReferencesRonald J. Prineas, M.B., B.S., Ph.D.
School of Medicine University of Miami, Miami, FL 33136Lawrence H. Kushi, Sc.D.
Aaron R. Folsom, M.D.
Roberd M. Bostick, M.D.
Ying Wu
School of Public Health University of Minnesota, Minneapolis, MN 554541
Fraser GE ,Sabate J ,Beeson WL ,Strahan TM . A possible protective effect of nut consumption on risk of coronary heart disease: the Adventist Health Study. Arch Intern Med 1992;152:1416-1424
CrossRef | Web of Science | Medline2
Folsom AR ,Kaye SA ,Sellers TA , et al. Body fat distribution and 5-year risk of death in older women. JAMA 1993;269:483-487
CrossRef | Web of Science | Medline3
Munger RG ,Folsom AR ,Kushi LH ,Kaye SA ,Sellers TA . Dietary assessment of older Iowa women with a food frequency questionnaire: nutrient intake, reproducibility, and comparison with 24-hour dietary recall interviews. Am J Epidemiol 1992;136:192-200
Web of Science | Medline
Author/Editor Response
The authors reply:
To the Editor: We concur with Dr. Mogadam that nuts may provide antiatherogenic benefits in addition to their cholesterol-lowering effect. Only walnuts, however, contain high amounts of alpha-linolenic acid (6.3 g per 100 g). Almonds, pistachios, and pecans contain 0.4, 0.3, and 0.7 g per 100 g of nut,1 respectively. These amounts are probably too low to have a measurable effect on platelet function. Although most nuts are high in antioxidant tocopherols, the effect on LDL oxidation is speculative. Further analyses are now under way to study other potential mechanisms.
It was gratifying to see duplication of our epidemiologic results2 by Prineas et al. Their results lend additional validity to the findings of the Adventist Health Study and increase the plausibility of a causal association.
We disagree with Mann's argument that the reduction of serum cholesterol levels by the walnut diet can be explained by differences in trans fatty acids. Direct measurements of the trans-fatty-acid content of our experimental diets are not available. The figure of 12.5 percent for the total fat intake from trans fatty acids in the average American diet, quoted by Mann, is probably too high,3 and no doubt higher than the content of our low-fat experimental diets. Nevertheless, assuming the “12.59 percent” figure for our control diet, calculations indicate that the maximal possible difference in trans-fatty-acid values between the experimental diets is about 7 percent of the total fat, or 2 percent of energy intake.
It is not plausible that a 2 percent caloric difference in trans fatty acids could explain the observed 22.4-mg decrease in the total serum cholesterol level. Mensink and Katan4 found a difference of 10 percent in calories derived from trans fatty acids; the serum cholesterol response was only 12 mg per deciliter. Differences in trans fatty acids may explain only a very small portion of the cholesterol-lowering effect of our walnut diet.
Dr. Mirkin suggests that the effect of walnuts was due to the fact that they replaced eggs, dairy products, and visible oils in the diet. The fat in the walnuts, however, replaced equivalent portions of all fats (saturated, monounsaturated, and polyunsaturated) in the control diet. The point of our study, as stated, was that the nutritional characteristics of walnuts were superior to those of the traditional fatty foods that they replaced. To this extent, we can agree with Mirkin. His interpretation of our epidemiologic findings is not supported by the Adventist Health Study data. We have responded in detail to his concerns elsewhere5.
5 ReferencesJoan Sabate, M.D.
Gary E. Fraser, M.B., Ch.B., Ph.D.
Loma Linda University, Loma Linda, CA 923501
Composition of foods: nuts and seed products. Washington, D.C.: Department of Agriculture, 1984. (Agricultural handbook no. 8-12.)
2
Fraser GE ,Sabate J ,Beeson WL ,Strahan TM . A possible protective effect of nut consumption on risk of coronary heart disease: the Adventist Health Study. Arch Intern Med 1992;152:1416-1424
CrossRef | Web of Science | Medline3
Hunter JE. Safety and health effects of isomeric fatty acids. In: Chow CK, ed. Fatty acids in food and their health implications. New York: Marcel Dekker, 1992.
4
Mensink RP ,Katan MB . Effect of dietary trans fatty acids on high-density and low-density lipoprotein cholesterol levels in healthy subjects. N Engl J Med 1990;323:439-445
Full Text | Web of Science | Medline5
Fraser GE ,Sabate J ,Beeson WL . Reply to: Nuts do not prevent heart attacks. Arch Intern Med 1993;153:125-125
CrossRef | Web of Science
- Citing Articles (2)
Citing Articles
1
Iwona Rudkowska, Peter JH Jones. (2007) Functional foods for the prevention and treatment of cardiovascular diseases: cholesterol and beyond. Expert Review of Cardiovascular Therapy 5:3, 477-490
CrossRef2
(1994) Health-Related Claims at Fast-Food Chains. New England Journal of Medicine 330:26, 1908-1909
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