Australian Walnut Industry Association

FACT FILE: WALNUTS

By Jayne Tancred ND

Want a simple and delicious way to make your diet more heart-healthy? Learn to love walnuts!  Toss them into salads, add them to your morning muesli or fruit salad, bake them in brownies, or use them to make pesto. There’s a myriad of options, so get munching – your heart will thank you!

Evidence from several large population studies shows the frequent consumption of nuts has a protective effect against heart disease.

For example, the Adventists Health Study tracked the health of over 34,000 Seventh Day Adventists over a period of 12 years.  Being predominantly vegetarian, non-smoking, and non-drinking, the Seventh Day Adventist community is a particularly healthy one.  Even after allowing for these confounding factors (which may have meant the evidence from this research couldn’t be applied to those of us who are less virtuous in our habits), regularly eating nuts offered significant protection from heart disease.  In fact, people in this study who ate nuts 4-5 times a week were only around half as likely to develop heart disease as those who ate nuts once a week or less.

By preventing or postponing the development of heart disease, eating nuts on a regular basis may even add years to your life – in the Adventists Health Study, heart disease occurred about 4 years later in those who frequently ate nuts (5 serves per week) compared to those who ate them infrequently.  This translated to an increased life expectancy of around 5 ½ years!

Walnuts in particular have been the subject of much research, and including them in your diet on a regular basis has been scientifically shown to reduce cholesterol levels and also improve other markers of cardiovascular health.

The results of at least 5 trials (involving more than 200 people) demonstrate that the cholesterol-lowering properties of a heart healthy diet can be boosted through the addition of walnuts.  The trials consistently show decreased levels of total cholesterol and LDL-cholesterol (that’s the ‘bad’ variety) – sometimes by as much as 9-12% over a period of only a few weeks.  Some trials have also shown improvements in the ratio of the ‘good’ HDL-cholesterol to LDL.

These cholesterol-lowering effects occur in people with both normal and high cholesterol levels, in healthy people, and in those with diabetes (who have increased risk of cardiovascular disease).  Importantly, walnuts still seem to work to a certain extent even if patients simply add them to their regular diet, although it’s preferable to include them as part of a heart-healthy eating plan that’s low in saturated fat.  And if you are worried about your fat intake, you’ll be reassured to know that in the clinical trials, adding walnuts to the diet didn’t result in an increase in body weight.

Why are walnuts so great? We don’t know all the answers yet, but we do know that they have a unique fatty acid profile plus a number of vitamins, minerals and other compounds that exert potent antioxidant effects.  All of these add up to give walnuts extraordinary capacity to fight heart disease and free radical damage.

The good oil:  Whilst most nuts contain high levels of monounsaturated fatty acids (such as oleic acid), walnuts are rich in polyunsaturates, specifically alpha-linolenic acid (ALA), one of the omega-3 fatty acids.  ALA is in the same class of fats as EPA and DHA – the protective omega-3 oils found in fish.  Eating a walnut-rich diet actually increases your levels of EPA and DHA, because your body can produce these from ALA.  So, like flaxseed, walnuts are a great source of omega-3s for vegetarians – in fact they contain more omega-3s than any other nut. 

ALA is believed to help prevent cardiovascular disease via a number of mechanisms. For example, it helps prevent heart arrhythmias, aids the maintenance of blood vessel health by inhibiting the deposition of plaque in the arteries, and helps keep your blood pressure on an even keel.

Arginine:  Most people are now aware that plant-foods offer more protection against heart disease than animal-foods.  One of the reasons behind this phenomenon is that the amino acids lysine and arginine are found in different ratios in plants.  A low lysine:arginine ratio is considered particularly beneficial for cardiovascular health. Walnuts are high in arginine, with relatively low levels of lysine – giving them a ratio of 0.16.  This is an excellent balance – especially when compared to an animal-derived food such as whole milk, which has a ratio of 2.44.

Arginine is required for the production of a compound called nitric oxide which acts as a relaxant on the blood vessels, playing an important role in maintaining blood pressure. It is also involved in arterial health and inhibits clotting in the blood.

Antioxidants:  Walnuts are one of the most abundant sources of antioxidants in the world, and this is probably one of the reasons they exert such strong effects against cardiovascular disease. 

It’s widely known that they are a good source of vitamin E, but they also contain at least 15 other antioxidants that you may be less familiar with. These include ellagic acid (also found in strawberries), which has an anti-cancer action.  As recently as 2003, researchers found three antioxidant compounds in walnuts that had never been identified before.

Manganese and copper:  The antioxidants in walnuts are backed up by manganese and copper.  These trace minerals are both essential co-factors in a number of vital pathways for antioxidant defences, including the enzyme superoxide dismutase (SOD). 

Magnesium:  Walnuts contain around 158mg of magnesium per 100g.  Magnesium has anti-spasmodic properties on the blood vessels and is essential for heart health.

Folic acid: Gram for gram, walnuts contain around 2/3 as much folate as spinach does – so they’re a valuable addition to your heart health from that point of view too, helping to reduce levels of homocysteine in the blood.

Beta-sitosterol: Like other nuts, walnuts contain beta-sitosterol, a sterol compound that seems to have a blocking effect, preventing cholesterol being absorbed into the bloodstream.

Melatonin:  Better known for its mood and sleep-cycle regulating properties, melatonin is also a potent antioxidant.  In addition to being produced by the pineal gland, melatonin is sourced in minute quantities from the diet.  In 2005 researchers at the University of Texas detected its presence in walnuts.  We are talking really tiny amounts here – only around 3 nanograms of melatonin per gram (one nanogram = one billionth of a gram), but even so, animal studies show this is enough to increase circulating levels of melatonin when walnuts are added to the diet.  Researchers postulate that this may be sufficient to delay the onset or reduce the severity of cardiovascular diseases and neurodegenerative conditions such as Alzheimer’s and Parkinson’s diseases.

So, how many walnuts should you eat? Most of the clinical trials have used large quantities of walnuts (as much as 84g per day).  A more realistic target is around 30g per day – that’s around six whole walnuts.  Experts estimate that by adding this quantity of walnuts to your daily diet, you’ll get a similar impact on your cholesterol levels to adding a serve of oat-bran every day – probably a reduction of around 4% over time. 

Hint: If you buy them already shelled, don’t forget that you’ll need 12 pieces of kernels to make up six walnuts, because there are two portions inside every shell.  It’s better to buy small quantities often, from a store with fast turnover, and keep them in an airtight container in the fridge.  Walnuts will go rancid quickly, and their nutritional quality declines rapidly. Levels of vitamin E are reduced by around 30% after three months of refrigerated storage.

Jayne Tancred is a naturopath, nutritionist and herbalist with a special interest in the role of diet in creating long-term health and preventing disease.

This article first appeared in Nature & Health, Australia's leading magazine of natural health and alternative medicine. To subscribe, freecall 1800 807 760, or email subscriptions@yaffa.com.au.

Home
Up