Walnuts are a delicious way to add extra nutrition, flavor and crunch to a meal. While walnuts are harvested in December, they are available year round a great source of those all-important omega-3 fatty acids.

It is no surprise that the regal and delicious walnut comes from an ornamental tree that is highly prized for its beauty. The walnut kernel consists of two bumpy lobes that look like abstract butterflies. The lobes are off white in color and covered by a thin, light brown skin. They are partially attached to each other. The kernels are enclosed in round or oblong shells that are brown in color and very hard.  

Health Benefits

When it comes to their health benefits, walnuts definitely are not a hard nut to crack. This delicious nut is an excellent source of omega-3 essential fatty acids, a special type of protective fat the body cannot manufacture. Walnuts' concentration of omega-3s (a quarter-cup provides 90.8% of the daily value for these essential fats) has many potential health benefits ranging from cardiovascular protection, to the promotion of better cognitive function, to anti-inflammatory benefits helpful in asthma, rheumatoid arthritis, and inflammatory skin diseases such as eczema and psoriasis. In addition, walnuts contain an antioxidant compound called ellagic acid that supports the immune system and appears to have several anticancer properties.

Take Walnuts to Heart

Adding walnuts to your diet can be an important step in improving your cardiovascular health. Walnuts are an important source of monounsaturated fats-approximately 15% of the fat found in walnuts is healthful monounsaturated fat. A host of studies have shown that increasing the dietary intake of monounsaturated-dense walnuts has favorable effects on high cholesterol levels and other cardiovascular risk factors. One particular study compared the effects of a cholesterol-lowering Mediterranean diet with an adjusted Mediterranean diet in which 35% of the calories derived from monounsaturated fats came from walnuts. When following the walnut-rich diet, the 49 study participants were found to have lower levels of total cholesterol, LDL (the dangerous form) cholesterol and Lp(a) ("lipoprotein a," another lipid compound that increases blood clotting and, when elevated, is considered a risk factor for atherosclerosis).

In addition to their heart-protective monounsaturated fats, walnuts' concentration of omega-3 essential fatty acids is also responsible for the favorable effects walnut consumption produces on cardiovascular risk factors. Omega-3s benefit the cardiovascular system by helping to prevent erratic heart rhythms, making blood less likely to clot inside arteries (which is the proximate cause of most heart attacks), and improving the ratio of good (HDL) cholesterol to potentially harmful (LDL) cholesterol. Omega-3s also reduce inflammation, which is a key component in the processes that turn cholesterol into artery-clogging plaques.

Since walnuts contain relatively high levels of l-arginine, an essential amino acid, they may also be of special import when it comes to hypertension. In the body (specifically within those hard-working blood vessels), l-arginine is converted into nitric oxide, a chemical that helps keep the inner walls of blood vessels smooth and allows blood vessels to relax. Since individuals with hypertension have a harder time maintaining normal nitric oxide levels, which may also relate to other significant health issues such as diabetes and heart problems, walnuts can serve as a great addition to their diets.

A study published in Phytochemistry sheds further light on walnuts' cardioprotective benefits. Earlier research had already suggested that several polyphenolic compounds found in walnuts, specifically ellagic and gallic acid, possessed antioxidant activity sufficient to inhibit free radical damage to LDL cholesterol. In this new study, researchers identified 16 polyphenols, including three new tannins, with antioxidant activity so protective they describe it as "remarkable."

Walnuts' Antioxidants Play Key Role in their Heart-Healthy Benefits

Research published in the British Journal of Nutrition (Blomhoff R, Carlsen MH), which identified several nuts among plant foods with the highest total antioxidant content, suggests nut's high antioxidant content may be key to their cardio-protective effects.

Walnuts, pecans and chestnuts have the highest antioxidant content of the tree nuts, with walnuts delivering more than 20 mmol antioxidants per 3 ounces (100 grams). Peanuts (although technically, a legume) also contribute significantly to our dietary intake of antioxidants.

Nuts' high antioxidant content helps explain results seen in the Iowa Women's Health Study in which risk of death from cardiovascular and coronary heart diseases showed strong and consistent reductions with increasing nut/peanut butter consumption. Total death rates decreased 11% and 19% for nut/peanut butter intake once per week and 1-4 times per week, respectively.

Even more impressive were the results of a review study of the evidence linking nuts and lower risk of coronary heart disease, also published in the British Journal of Nutrition. (Kelly JH, Sabate J.) In this study, researchers looked at four large prospective epidemiological studies-the Adventist Health Study, Iowa Women's Study, Nurses' Health Study and the Physician's Health Study. When evidence from all four studies was combined, subjects consuming nuts at least 4 times a week showed a 37% reduced risk of coronary heart disease compared to those who never or seldom ate nuts. Each additional serving of nuts per week was associated with an average 8.3% reduced risk of coronary heart disease.

Practical Tip: To lower your risk of cardiovascular and coronary heart disease, enjoy a handful of walnuts, or other antioxidant-rich nuts, at least 4 times a week.

Walnuts Improve Cardiovascular Function by a Variety of Mechanisms

A study conducted at the Lipid Clinic in Barcelona, Spain, and published in Circulation reveals numerous ways through which walnuts promote healthy heart and blood vessel function.

For four weeks, 21 men and women with high cholesterol followed either a regular, low-calorie Mediterranean diet or one in which walnuts were substituted for about one-third of the calories supplied by olives, olive and other monounsaturated fats in the Mediterranean diet. Then, for a second four weeks, they switched over to the diet they had not yet been on.

Not only did the walnut diet significantly reduce total cholesterol (a drop that ranged from 4.4 to 7.4%) and LDL (bad) cholesterol (a drop ranging from 6.4 to 10%), but walnuts were also found to increase the elasticity of the arteries by 64%, and to reduce levels of vascular cell adhesion molecules, a key player in the development of atherosclerosis (hardening of the arteries).

The researchers found that the drop in cholesterol correlated with increases in blood levels of alpha-linolenic acid, a key essential fatty acid from which long chain omega-3 fats (such as EPA) can be derived, and gamma-tocopherol, a form of vitamin E. Walnuts are uniquely rich in both of these nutrients, which have shown heart protective benefits in other studies.

The U.S. Food and Drug Administration has recently cleared the health claim that "eating 1.5 ounces per day of walnuts as part of a diet low in saturated fat and cholesterol may reduce the risk of heart disease." "This is the first time a whole food, not its isolated components, has shown this beneficial effect on vascular health," said Emilio Ros, who led the study at the Hospital Clinic of Barcelona.

Walnuts Help Prevent and Control High Blood Pressure

Individuals whose diets provide greater amounts of omega-3 fatty polyunsaturated fatty acids-and walnuts are an excellent source of these essential fats-have lower blood pressure than those who consume less, shows data gathered in the International Study of Macro- and Micro-nutrients and Blood Pressure (INTERMAP) study (Ueshima H, Stamler J, et al. Hypertension).

The INTERMAP is a study of lifestyle factors, including diet, and their effect on blood pressure in 4,680 men and women aged 40 to 59 living in Japan, China, the U.S. and the U.K. Blood pressure was measured and dietary recall questionnaires were completed by participants on four occasions. Dietary data was analyzed for levels of omega-3 fatty acids from food sources including fish, nuts, seeds and vegetable oils.

Average daily intake of omega-3 fatty acids was 2 grams. Participants with a high (o.67% kcal) omega-3 fatty acid percentage of their daily calorie intake had an average systolic and diastolic blood pressure reading that was 0.55/0.57 mm Hg less, respectively, than participants with lower intake. Previous research has found that a decrease of 2 mm Hg reduces the population-wide average stroke mortality rate by 6 percent and that of coronary heart disease by 4%.

Higher omega-3 fatty acid intake among the 2,238 subjects who were not using drugs, supplements, or a special diet for hypertension, heart disease, or diabetes was associated with a 1.01/0.98 mm Hg reduction in systolic and diastolic blood pressure, respectively.

For the 2,038 subjects in this group who did not have hypertension, greater intake was associated with a 0.91/0.92 mm Hg average systolic and diastolic reduction.

Lead author Hirotsugu Ueshima, MD of Shiga University of Medical Science in Japan, noted that the beneficial effect of omega-3 fats was even greater in people who had not yet developed high blood pressure.

The researchers also found that omega-3s from nuts, seeds, and vegetable oils-such as walnuts and flaxseed-had just as much impact on blood pressure as omega-3s from fish. "With blood pressure, every millimeter counts. The effect of each nutrient is apparently small but independent, so together they can add up to a substantial impact on blood pressure. If you can reduce blood pressure a few millimeters from eating less salt, losing a few pounds, avoiding heavy drinking, eating more vegetables, whole grains and fruits (for their fiber, minerals, vegetable protein and other nutrients) and getting more omega-3 fatty acids, then you've made a big difference," said Ueshima.

Walnuts Improve Cholesterol Profile in Persons with Type 2 Diabetes

In patients with type 2 diabetes, including a daily ounce of walnuts in a diet in which 30% of calories came from fat translated into a significant improvement in subjects' cholesterol profile.

In this study, published in Diabetes Care, 58 men and women with an average age of 59 years, were assigned to one of three diets in which 30% of calories was derived from fat: a low fat diet, a modified low fat diet, and a modified low fat diet including an ounce of walnuts per day.

After 6 months, those on the walnut diet had achieved a significantly greater increase in their HDL-to-total cholesterol ratio than the other groups, plus walnut eaters saw a 10% reduction in their LDL cholesterol. Why such benefit from walnuts? Most likely because walnuts are exceptionally high in their content of monounsaturated fat and the omega-3 fatty acid, alpha-linolenic acid. Plus, walnuts combine these heart healthy fats with a hefty dose of the antioxidants including at least 16 antioxidant phenols, vitamin E, ellagic and gallic acid.

Additional research has confirmed that when walnuts are eaten as part of a modified low-fat diet, the result is a more cardiprotective fat profile in diabetic patients than can be achieved by simply lowering the fat content of the diet. In a study published in the Journal of the American Dietetic Association, all 55 study participants with type 2 diabetes were put on low fat diets, but the only group to achieve a cardioprotective fat profile (less than 10% of calories from saturated fat, 7-10% of calories from polyunsaturated fats, adequate omega-3 fats, and an omega-6:omega-3 ratio of less than 10) were those who ate walnuts (30 grams-about one ounce-per day).

Walnuts Found to Reduce Levels of Several Molecules that Promote Atherosclerosis

In addition to walnuts' beneficial effects on cholesterol, more insight into the reasons why walnuts reduce the risk of coronary heart disease were revealed in research published in the Journal of Nutrition.

The study involved 20 overweight or obese men, 30 to 60 years old, and 3 menopausal women, aged 55-65, all of whom had elevated LDL cholesterol levels. Each subject was assigned to one of the three diets on a rotating six-week basis with a two-week break between each one. The average American diet served as the control diet, while the two experimental diets were a linoleic acid (LA) diet that included an ounce of walnuts and a teaspoon of walnut oil daily, and an alpha-linoleic acid diet (ALA), which added a teaspoon of flaxseed oil, which is especially high in ALA, to the linoleic diet.

Both experimental diets resulted in positive effects, with the ALA diet providing the most benefit. In addition to lowering LDL cholesterol, the walnut-rich ALA diet:

• lowered levels of C-reactive protein, a marker of inflammation strongly associated with atherosclerosis and heart disease

• increased levels of the protective omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and

• decreased levels of ICAM-1 and VCAM-1 and E-selection, all of which are involved in cholesterol's adhesion to the endothelium (the lining of the arteries).

Walnuts Protect Arteries after High-Fat Meal

Walnuts, a rich source of the omega-3 fat, alpha-linolenic acid (ALA), improve artery function after a high fat meal and may be even more important in a Mediterranean-type diet than olive oil in promoting heart health, suggests a small study from Spain (Cortes B, Nunez I, J Am Coll Cardiol).

The study, funded by the California Walnut Commission and the Spanish Ministry of Health, looked at the effects on a number of markers of cardiovascular health of adding walnuts or olive oil to a fatty meal.

Twelve healthy people and 12 patients with high cholesterol levels were randomly assigned to eat either a high-fat meal (80 g fat, 35 per cent saturated fat) that also included 40 grams of walnuts or one that included 25 grams of olive oil (30 grams = 1 ounce). After one week, the participants eating walnuts were crossed over to olive oil and visa versa.

The researchers evaluated the activity of the subjects' blood vessels after the meal, and looked at cholesterol and triglyceride levels, as well as markers of free radical (oxidative) stress and blood levels of asymmetric dimethylarginine (ADMA). AMDA is a by-product of the metabolism of the protein, arginine, that is said to interfere with the amino acid L-arginine, which is involved in the production of nitric oxide (NO). NO acts upon smooth muscle in blood vessels, causing them to dilate and thus increasing blood flow.

The researchers reported that blood flow in the brachial artery of the arm, (flow-mediated dilation) increased 24% in the subjects with high cholesterol after they ate the walnut-containing meal, while the olive oil-containing meal actually resulted in a 36% decrease in blood flow.

However, levels of cholesterol and triglycerides decreased in similar amounts after both meals. Blood levels of ADMA were not affected by either walnuts or olive oil. The fact that a single walnut meal positively affects postprandial vasoactivity further supports the beneficial effects of walnuts on cardiovascular risk, wrote lead author Berenice Cortés in the Journal of the American College of Cardiology.

E-selectin, a molecule that plays a role in cell adhesion-the process by which damaged cholesterol adheres to blood vessel walls to form plaques-also fell after the walnut meal. 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., said Dr. Ross. Robert Vogel, a researcher from the University of Maryland, who did not participate in the study, commented: This demonstrates that the protective fat from walnuts actually undoes some of the detrimental effects of a high-saturated-fat diet, whereas a neutral fat, such as olive oil, does not have as much protective ability>,/q> This raises a very interesting issue because many people who eat a Mediterranean diet believe the olive oil is providing the benefits. But this research and other data indicate that's not true…There are probably other factors in the diet, including that it is a relatively rich source of nuts. This is not to say that olive oil is bad, but it's not the key protective factor in the Mediterranean diet, said Vogel. 

This does not mean that simply eating a handful of walnuts can make up for an unhealthy diet. Consumers would get the wrong message from our findings if they think they can continue eating unhealthy fats provided they add walnuts to their meals,said study author Emilio Ros from the Universitat Autonoma de Barcelona. While this research clearly indicates that nuts are highly beneficial, they are only one component of the Mediterranean diet. Rich in vegetables, fruits, legumes, whole grains, fish and olive oil, as well as nuts, the Mediterranean diet includes literally thousands of protective vitamins, minerals and phytonutrients. It's the combination of all these beneficial compounds that explains why this healthy way of eating is associated with longer life and protection against numerous diseases including cardiovascular disease, cognitive decline, and a number of cancers.

A Source of Bio-Available Melatonin

Want a better night's sleep? Try sprinkling your dinner's tossed green salad, fruit salad or steamed vegetables with a handful of walnuts. Or enjoy a baked apple or poached pear topped with walnuts for dessert.

Melatonin, a hormone produced by the pineal gland, which is involved in inducing and regulating sleep and is also a powerful antioxidant, has been discovered in walnuts in bio-available form, making them the perfect evening food for a natural good night's sleep.

Melatonin has been shown to help improve sleep for night shift workers and people suffering from jet lag, but maintaining healthy levels of this hormone is important for everyone over the age of 40 since the amount of melatonin produced by the human body decreases significantly as we age, and this decrease in antioxidant protection may be related to the development of free radical-related diseases later in life.

In a study published in Nutrition, Russell Reiter and colleagues at the University of Texas have not only quantified the amount of melatonin present in walnuts-between 2.5 and 4.5 ng/gram-but have demonstrated that eating walnuts triples blood levels of melatonin and also increases antioxidant activity in the bloodstream in animals.

The authors theorize that by helping the body resist oxidative stress (free radical damage), walnuts may help reduce the risk of cancer and delay or reduce the severity of cardiovascular disease and neurodegenerative diseases such as Parkinson's or Alzheimer's disease. Walnuts, best known as a heart-healthy nut, are also a rich source of another highly cardio-protective nutrient: omega-3-fatty acids, so Reiter and his team will next investigate possible synergy between walnuts' omega-3 fats and melatonin. To us at the World's Healthiest Foods, this sounds familiar theme in Nature's symphony in which whole, wholesome foods each provide a wealth of nutrients whose harmony promotes our optimal health.

Omega-3-rich Walnuts Protect Bone Health

Alpha linolenic acid, the omega-3 fat found in walnuts, promotes bone health by helping to prevent excessive bone turnover-when consumption of foods rich in this omega-3 fat results in a lower ratio of omega-6 to omega-3 fats in the diet.(Griel AE, Kris-Etherton PM, et al. Nutrition Journal)

Other studies have shown that diets rich in the omega-3s from fish (DHA and EPA), which also naturally result in a lowered ratio of omega-6 to omega-3 fats, reduce bone loss. Researchers think this is most likely because omega-6 fats are converted into pro-inflammatory prostaglandins, while omega-3 fats are metabolized into anti-inflammatory prostaglandins. (Prostaglandins are hormone-like substances made in our bodies from fatty acids.)

In this study, 23 participants ate each of 3 diets for a 6-week period with a 3 week washout period in between diets. All 3 diets provided a similar amount of fat, but their ratio of omega-6 to omega-3 fats was quite different:

Diet 1 provided 34% total fat with omega-6 and omega-3 fats in amounts typically seen in the American diet: 9% polyunsaturated fats (PUFAs) of which 7.7% were omega-6 and only 0.8% omega-3 fats, resulting in a pro-inflammatory ratio of 9.6:1.

Diet 2, an omega-6-rich diet, provided 37% total fat containing 16% PUFAs of which 12% were omega-6 and 3.6% omega-3, a better but still pro-inflammatory ratio of 3.3:1.

Diet 3, which provided 38% in total fats, was an omega-3-rich diet, containing 17% PUFAs, of which 10.5% were omega-6 and 6.5% omega-3, resulting in an anti-inflammatory ratio of 1.6:1.

After each diet, subjects' blood levels of N-telopeptides, a marker of bone breakdown, were measured, and were found to be much lower following Diet 3, the omega-3-rich diet, than either of the other two.

The level of N-telopeptides seen in subjects' blood each diet also correlated with that of a marker of inflammation called tumor necrosis factor-alpha (TNF-alpha). Diets 1 and 2-the diets which had a significantly higher ratio of omega-6 to omega-3 fats-also had much higher levels of TNF-alpha than the Diet 3, which was high in omega-3 fats from walnuts and flaxseed. Practical Tip: Protect your bones' by making anti-inflammatory omega-3-rich flaxseed and walnuts, as well as cold water fish, frequent contributors to your healthy way of eating.

Protective Omega-3 Levels Greatly Improved by Eating Just 4 Walnuts a Day

Enjoying just 4 walnuts a day significantly increased blood levels of the health-protective omega-3 essential fatty acids, alpha linolenic acid (ALA) and eicosapentaenoic acid (EPA), in 10 adults.

EPA, a longer-chain omega-3 fat, is already present in cold water fish, but is not found in nuts, which contain the shorter-chain omega-3 fat, ALA. Fortunately, as this study confirms, our bodies can make EPA from the ALA provided by walnuts, which are its richest source among all the nuts.

After a 2-week run-in period, during which no walnuts were eaten, blood levels of ALA and EPA were assessed, and study participants then ate 4 walnuts a day, in addition to their regular diet, for 3 weeks.

When blood tests were again run, significant increases in levels of ALA (from 0.23 to 0.47) and EPA (from 0.23 to 0.82) were seen. And levels of ALA and EPA remained elevated over subjects' initial levels even after a final 2-week period during which no walnuts were eaten. This study, published in Nutrition, Metabolism and Cardiovascular Diseases, clearly shows that even a very simple change in diet can have highly beneficial and lasting effects on our health. Boosting your body's supply of cardio-protective, anti-inflammatory omega-3 fatty acids couldn't be any easier-just add a few walnuts to your morning cereal or daily salad or just grab a handful for an afternoon snack.

Eating Nuts Lowers Risk of Weight Gain

Although nuts are known to provide a variety of cardio-protective benefits, many avoid them for fear of weight gain. A prospective study published in the journal Obesity shows such fears are groundless. In fact, people who eat nuts at least twice a week are much less likely to gain weight than those who almost never eat nuts.

The 28-month study involving 8,865 adult men and women in Spain, found that participants who ate nuts at least two times per week were 31% less likely to gain weight than were participants who never or almost never ate nuts.

And, among the study participants who gained weight, those who never or almost never ate nuts gained more (an average of 424 g more) than those who ate nuts at least twice weekly.

Study authors concluded, "Frequent nut consumption was associated with a reduced risk of weight gain (12 lbs or 5 kg or more). These results support the recommendation of nut consumption as an important component of a cardioprotective diet and also allay fears of possible weight gain."

Practical Tip: Don't let concerns about gaining weight prevent you from enjoying the delicious taste and many health benefits of nuts!