New studies continue to affirm the cardiac benefits of the only common nut rich in omega-3s
by Craig Weatherby
There’s already a wealth of evidence that nuts are good for cardio health and weight control.
And the results of two studies published earlier this year lend support to walnuts’ reputation as heart-healthy snacks.
of omega-3 ALA
The short-chain omega-3 called ALA is most abundant in these foods, in descending order of abundance:
- Flaxseed and its oil (57 percent of fatty acids)
- Walnuts (15 percent of fatty acids)
- Legumes (meaningful amounts in beans, peas and split peas)
- Dark greens like kale and spinach (minuscule amounts)
While the long-chain omega-3s in fish fat are much more beneficial, it makes sense to get omega-3s in every form possible, especially when they are inherently healthful foods, as these are.
There are good reasons why walnuts should possess even greater preventive-health powers than their nutty cousins.
In addition to offering ample artery-friendly antioxidants and amino acids (L-arginine), walnuts are the only common nuts abundant in heart-healthy omega-3 fatty acids: specifically, the short-chain omega-3 fatty acid called alpha-linolenic acid (ALA).
Diets high in ALA test heart-healthy--albeit less beneficial than marine omega-3s--for two reasons:
- The body converts some five to 20 percent of dietary ALA into the long-chain omega-3s found only in fish and other aquatic foods. Compared with ALA, long-chain omega-3s deliver much greater benefits with regard to cardiovascular health, diabetes, cancer, and depression.
- Minor amounts of dietary ALA get incorporated into cell membranes, where it exerts anti-inflammatory influences, enhances arterial health, and may help prevent dangerous arrhythmias.
With this background in mind, let’s take a look at the new findings.
Study #1: Walnuts aid artery function more than “pure” olive oil
The results of a small study from Spain suggest that walnuts—an overlooked part of traditional, heart-healthy Mediterranean-type diets—could improve artery function and heart health (Cortes B et al 2006).
The lead author, Dr. Emilio Ros, explained the cardiovascular context in the preamble to the positive results of a human study he published two years ago (Ros E et al 2004), which showed that walnuts yield highly beneficial effects in the endothelial tissues that line our arteries and directly affect the ease of blood flow:
- “Epidemiological studies suggest that nut intake decreases coronary artery disease (CAD) risk.”
- “Nuts have a cholesterol-lowering effect that partly explains this benefit. Endothelial dysfunction is associated with CAD and its risk factors and is reversed by antioxidants and marine n-3 [omega-3] fatty acids.”
- “Walnuts are a rich source of both antioxidants and alpha-linolenic acid, a plant n-3 [omega-3] fatty acid.”
While press summaries suggested that the study proved walnuts more beneficial than olive oil, those reports failed to note a critically important distinction between “pure” (refined) olive oil and “extra virgin” (unrefined) olive oils: a distinction the study authors also failed to make.
Unlike the heavily refined “pure” grade oil used in this study--which contains none of olive oil’s naturally occurring antioxidants--extra virgin grade olive oil (EVOO) is rich in potent polyphenol antioxidants, and has been proven far superior to pure grade olive oil in terms of enhancing arterial performance and other markers of cardiovascular health.
In fact, prior studies demonstrated that the antioxidants in EVOO exert some of the same beneficial effects on blood and arteries produced in this study by walnuts, including enhanced performance in the endothelial lining of people’s arteries (see “Extra Virgin Olive Oil Confirmed as Best Cardiac Prevention Choice” and “Antioxidant Unique to Extra Virgin Olive Oil Protects Mouse Brain Cells”).
Leaving this inexplicable oversight aside for the moment, the study gave walnuts another big hearth-health boost.
The research team, based at the Universitat Autonoma de Barcelona, recruited 12 healthy people and 12 with high cholesterol levels and compared the cardiac effects of walnuts and pure grade olive oil in each group.
All of the participants consumed a meal high in fat (35 percent saturated fat). Half of the participants, chosen randomly from both groups, were given 40 grams (1.4 ounces) of walnuts in addition to the meal, while the other half consumed 25 grams (just under one ounce) of olive oil in addition to the meal.
One week later, the participants repeated the high-fat meal, but switched from consuming supplemental nuts to consuming supplemental olive oil, and vice versa.
Following both meals, the researchers analyzed the participants’ blood vessels, blood flow, cholesterol levels, and levels of oxidative stress.
The Barcelona researchers reported that blood flow improved in the high cholesterol group after consuming a walnut-supplemented meal.
In contrast, the olive oil-supplemented meal actually resulted in a decrease in blood flow, probably because the olive oil simply added more fat (none of it proven to enhance artery performance) to the picture.
Given the results of prior studies, it’s highly likely that if the participants had been given EVOO instead of pure grade oil, they would have experienced an increase in blood flow in stead of a decrease.
Nonetheless, as the authors wrote, “The fact that a single walnut meal positively affects postprandial vasoactivity [performance of arteries after a fatty meal] further supports the beneficial effects of walnuts on cardiovascular risk.”
And, as Dr. Ros told the press, “Many people forget that walnuts are an important part of the Mediterranean diet, providing numerous health benefits. Walnuts, unlike olive oil and other nuts, contain significant amounts of polyunsaturated fatty acids, specifically alpha-linolenic acid (ALA), an essential plant based omega-3. They also provide antioxidants and L-arginine, components identified in past studies as potential nutrients that improve artery function.”
This study confirms that walnuts are good for arteries, and while it proves them artery-friendlier than refined, “pure” grade olive oil it does not prove anything about their benefits versus those of EVOO, which appear comparable.
Study #2: Walnuts aid hamsters’ arteries
The results of the Barcelona study summarized above were echoed in an animal study conducted jointly by scientists from the USDA Agricultural Research Service (ARS), the University of California, and Italy’s University of Padova (Davis P et al 2006).
Most significantly, they support findings from the similar human study led by Dr. Emilio Ros, cited above (Ros E et al 2004).
One hundred hamsters were given a high-fat, cholesterol-raising diet, supplemented with three to eight handfuls of walnuts a day or one of two forms of vitamin E (gamma- or alpha-tocopherol), for six months.
As seen in the 2004 human study from Dr. Ros' team, the hamsters fed ground walnuts enjoyed reduced levels of a protein called endothelin, which promotes cardiovascular disease by inflaming arterial tissues (The vitamin E groups showed no such benefits).
Arterial inflammation reduces blood flow and promotes buildup of the fatty plaques that clog blood vessels and can burst, causing heart attacks and strokes.
The researchers made several key comments (clarifying insertions in brackets ):
- “The study results are consistent with those of human walnut feeding studies and suggest that the mechanisms underlying those results are mediated in part by endothelin-dependent mechanisms.”
- “The contrasting results… also make it unlikely that the… effects of walnuts are due to their [vitamin E] content.”
- “Finally, the results indicate that the walnut fat compartment is a likely location for the components responsible [i.e., omega-3 ALA]...”
In addition to their cardiac benefits, walnuts, almonds, cashews, and hazelnuts, and other common nuts are proven to suppress appetite and help prevent weight gain. So next time you’ve got a little hunger craving, keep your heart and gut in mind, and pass on the chips in favor of a few nuts!
- Cortes B, Nunez I, Cofan M, Gilabert R, Perez-Heras A, Casals E, Deulofeu R, Ros E. Acute effects of high-fat meals enriched with walnuts or olive oil on postprandial endothelial function. J Am Coll Cardiol. 2006 Oct 17;48(8):1666-71. Epub 2006 Sep 26.
- Davis P, Valacchi G, Pagnin E, Shao Q, Gross HB, Calo L, Yokoyama W. Walnuts reduce aortic ET-1 mRNA levels in hamsters fed a high-fat, atherogenic diet. J Nutr. 2006 Feb;136(2):428-32.
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- Zambon D, Sabate J, Munoz S, Campero B, Casals E, Merlos M, Laguna JC, Ros E. Substituting walnuts for monounsaturated fat improves the serum lipid profile of hypercholesterolemic men and women. A randomized crossover trial. Ann Intern Med. 2000 Apr 4;132(7):538-46. Erratum in: Ann Intern Med 2000 Oct 17;133(8):659.
- Almario RU, Vonghavaravat V, Wong R, Kasim-Karakas SE. Effects of walnut consumption on plasma fatty acids and lipoproteins in combined hyperlipidemia. Am J Clin Nutr. 2001 Jul;74(1):72-9.
- Chisholm A, Mann J, Skeaff M, Frampton C, Sutherland W, Duncan A, Tiszavari S. A diet rich in walnuts favourably influences plasma fatty acid profile in moderately hyperlipidaemic subjects. Eur J Clin Nutr. 1998 Jan;52(1):12-6.
- Landmark K, Alm CS. [Alpha-linolenic acid, cardiovascular disease and sudden death.] Tidsskr Nor Laegeforen. 2006 Nov 2;126(21):2792-2794. Norwegian.
- Ros E, Nunez I, Perez-Heras A, Serra M, Gilabert R, Casals E, Deulofeu R. A walnut diet improves endothelial function in hypercholesterolemic subjects: a randomized crossover trial. Circulation. 2004 Apr 6;109(13):1609-14. Epub 2004 Mar 22.