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Walnuts: an unique source of alpha-linolenic acid

Walnuts are nuts with an extra benefit. In addition to the fact that they contain fibres, vitamin E and protein, walnuts are among the few foodstuffs that contain large amounts of alpha-linolenic acid.

Alpha-linolenic acid is classified as an essential fat. Consequently dietary intake is our only means of achieving an adequate intake of this important macronutrient. However in our western diet an average intake that reaches the recommended levels of 2 g per day (recommendation of Eurodiet) isn’t very common (table 1).

Alpha-linolenic acid is an important building block for the cell membranes in our body. Additionally more and more studies link alpha-linolenic acid to heart benefits, an interesting fact when bearing in mind that cardiovascular diseases account for over 4.3 million deaths in Europe yearly. This equals 48% of the total deaths per year.

Walnuts are therefore an interesting research topic and much research is carried out in this area. In this issue two scientific experts will shed light on the latest research regarding walnuts and several cardiovascular risk factors.

Walnuts cut cholesterol levels

Consumption of nuts has been associated with positive cardiovascular disease health outcomes, including decreased risk in death (1,2). Walnuts in particular have received attention in research endeavours owing to their unique macronutrient and micronutrient composition. While most nuts are high in monounsaturated fatty acids, walnuts are composed largely of polyunsaturated fatty acids (47.2 g per 100 g of walnuts), especially alpha-linolenic acid (9.1 g) and linoleic acid (38.1 g) (3).

Deirdre K. Thomas American science expert on nuts, USA

In a recent meta-analysis, we found that consumption of walnut–enriched diets for 4-24 weeks significantly reduced serum cholesterol concentrations over 10 mg/dL more than the control diets (4). However, our pooled results did not show a significant benefit for high-density lipoproteins or triglycerides. Other short-term clinical findings indicated that walnuts provided significant benefits for antioxidant capacity and inflammatory markers. Importantly, weight gain was not observed in these trials (5-7).

The studies included in our analysis incorporated walnuts to comprise 10-24% of total calories consumed. Mechanisms by which walnuts could beneficially affect cholesterol levels and other cardiovascular risk factors have been posed (8). These include simply replacing saturated fatty acids in the diet with healthier unsaturated fatty acids, or by components acting explicitly on various pathways in cardiovascular disease development. The current evidence indicates walnuts can be incorporated into one’s diet for the improvement of cardiovascular risk factors, namely, lipid profiles.

Deirdre K. Thomas, American Science expert on nuts, USA

Sources: (a comprehensive list can be requested via info@aboutnuts.nl)
1. Kris-Etherton P.M. et al. Nutrition Reviews 2001; 59: 103-11.
2. Hu F.B., Stampfer M.J. Current Atherosclerosis Reports 1999; 1: 204-9.
3. Li L. et al. Journal of Agricultural and Food Chemistry 2007; 55: 1164-1169.
4. Banel D.K., Hu F.B. American Journal of Clinical Nutrition 2009; 90: 56-63.
5. Zhao G. et al. American Journal of Clinical Nutrition 2007; 85: 385-91.
6. Ros E. et al. Circulation 2004; 109: 1609-14.
7. Mukuddem-Petersen J. et al. British Journal of Nutrition 2007; 97: 1144-53.
8. Ros E., Mataix J. British Journal of Nutrition 2006; 96 (Suppl 2): S29-S35.

Walnuts improve endothelial function

Endothelial dysfunction is integral to the development of atherosclerosis and consequently cardiovascular disease. Two recent randomized controlled crossover trials in subjects with increased cholesterol concentrations (1) and subjects with type 2 diabetes (2) have shown that inclusion of walnuts in the diet for 4 and 8 weeks respectively, compared to a diet without walnuts, improved endothelial function.

Dr. Welma Stonehouse Associate Professor in Human Nutrition

In addition Cortes et al. (3) showed that adding walnuts to a high-fat, high saturated fatty acid meal counteracted the detrimental changes in endothelial function (measured by flow-mediated dilation) associated with eating a fatty meal. The consumption of walnut diets compared to control diets in three other studies also showed reductions in VCAM-1, a marker of endothelial function (systematic review by Banel & Hu (4)). These beneficial effects on the endothelium may be ascribed to the various components contained in walnuts. Compared to other nuts and plant-based food products, walnuts are exceptionally high in alpha-linolenic acid (an omega-3 polyunsaturated fatty acid), phenolics and dietary antioxidants and are a rich source of arginine.

The high content of antioxidants protects the endothelium from attack and damage by free radicals. Arginine, an essential amino acid, is required for the production of nitric oxide, which is one of the most critical substances produced by the vascular endothelium for the regulation of vasomotor tone. In addition, the serum cholesterol lowering effects of walnuts may also contribute to improving endothelial function by decreasing the build-up of cholesterol in fatty plaque (atherosclerosis).

A recent meta-analysis of 13 randomized controlled trials on walnut-enriched diets reported decreases in serum total cholesterol and LDL-cholesterol concentrations of 10.3 mg/dL (0.27 mmol/L) and 9.2 mg/dL (0.24 mmol/L) with intakes that ranged from 5-25% of total energy intake (30-108 g walnuts/day) (4). In conclusion, the inclusion of walnuts in the diet may improve endothelial function owing to its unique composition including alpha-linolenic acid, antioxidants, arginine and its cholesterol lowering properties which may act synergistically to affect endothelial function.

Dr. Welma Stonehouse, Associate Professor in Human Nutrition
Institute of Food, Nutrition and Human Health, Massey University

Sources: (a comprehensive list can be requested via info@aboutnuts.nl)
1. Ros E. et al. Circulation 2004; 109: 1609-14.
2. Ma Y. et al. Diabetes Care [Epub ahead of print] 2009.
3. Cortes B. et al. Journal of the American College of Cardiology 2006; 48: 1666-71.
4. Banel D.K., Hu F.B. American Journal of Clinical Nutrition 2009; 90: 56-63.

Walnuts and fatty fish benefit the heart in different ways

Fish and walnuts are both food products that are associated with heart benefits because they both contain omega-3 fatty acids. However, either of these foodstuffs could be off-limits, owing for instance to an allergy or a vegetarian lifestyle. To determine whether walnuts and fish have the same effects on heart health, researchers from the American Loma Linda University recently studied both omega-3 sources.

During the crossover intervention study, 25 normal to mildly hyperlipidemic subjects followed three different iso-energetic diets in four-week periods. The subjects were in random sequence assigned to a diet with no fish or nuts, a diet with salmon or a diet with walnuts, and there was a one-week wash out period between the different diets. The amounts of walnuts (42.5 g / day) and fatty fish (113 g / twice a week) in the diets were in accordance with the US food recommendations for heart health.

The study found favourable effects of consuming salmon twice per week or eating 42.5 g walnuts per day on risk factors for heart disease. The study also showed that both foods benefited other cardiovascular risk factors.

Eating walnuts on a daily basis showed a significant beneficial effect on several cholesterol markers, such as total cholesterol and LDL:HDL ratio compared to the diet with no fish or nuts or the salmon diet. The diet with salmon was on the other hand associated with a significant decrease in triglycerides.

The study shows that walnuts as a source of alpha-linolenic acid and fatty fish as a source of eicosapentaenoic acid and docosahexaenoic acid have significantly different beneficial effects on well-known risk markers for heart disease.

Source:
Rajaram S., Haddad E.H., Mejia A., Sabaté J. Walnuts and fatty fish influence different serum lipid fractions in normal to mildly hyperlipidemic individuals: a randomized controlled study. American Journal of Clinical Nutrition 2009; 89 (5): 1657S-1663S.

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Editorial staff
Intersnack Group, Düsseldorf
Schuttelaar & Partners, The Hague

Editorial Board
Schuttelaar & Partners, The Hague

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