Botanically-known as a Drupe or stone fruit, the walnut is actually a two-part edible seed and not a true nut in the traditional sense. The seed kernels are often pre-shelled and have a soft brown skin, rich in antioxidants protecting the inner fleshy seed, which contain polyunsaturated fats that are sensitive to oxygen and extreme heat. Components of the Juglans plant have been traditionally used to treat microbial infections, digestive concerns, thyroid disease and sinusitis.
Walnuts can be enjoyed raw, toasted or pickled. They are great in salads, cakes, and brownies or in a trail mix. Classically used in baklava, carrot cake or Waldorf salad, the versatility of this little ‘nut’ is impressive.
Walnuts are one of the oldest and best examples of a holistic medicine teaching known as the Doctrine of Signatures. It comes from the simple idea that ‘nature knows best’ and was coined in the European Middle Ages by herbalists and medicine men and women. The Doctrine of Signatures describes the wisdom of nature as it provides clues about the shape, form, colour, appearance or environment, which reveal a plant, herb or mineral’s hidden medicinal purposes. Modern medicine now supports what European cultures have long believed, with research to show various therapeutic uses of walnuts in human health.
The next time you see a walnut, take a good look at it. Walnuts have an uncanny resemblance to the human brain. Its shape; hemispheric division and wrinkles with a hard outer shell are all representative of the very part of the body it benefits. Interestingly, the brain is made up of mostly polyunsaturated fats, exactly the same as a walnut. Cool right? Mother nature knows what she’s doing.
In just over a tablespoon of walnuts (28g to be exact), you get around 7g of protein. This is the highest protein content among all nuts. 65% of their composition is from fat, and of that the majority is polyunsaturated fat. Walnuts are also particularly high in the trace mineral manganese. Like all nuts, walnuts are also rich in B vitamins, vitamin E and protective polyphenols.
Storage and cooking tips
The processing and storage of walnuts is important, mainly to prevent oxidation of the delicate fats within the kernel. Also, because shelled walnuts have their protective layer removed, they are susceptible to mould growth, which could lead to deleterious health effects. Similar to dried fruit, the risk of microspore mould growth is that it produces harmful cancer-causing Aflatoxins. Airtight, moisture-free packaging is essential, and once opened walnuts should be stored away from direct light and heat, preferably in the fridge.
To summarise the research, a 2018 meta-analysis of 1059 participants concluded that a walnut-enriched diet improved memory and cognition, had improvements in systemic inflammation, improved cholesterol profiles, reduced BMI and weight and improved cardiovascular function. Some specifics on the data and mechanisms of action are outlined below.
Various clinical trials have confirmed the therapeutic properties of walnuts in cognitive performance, memory, depression, stroke and overall brain health.
Pandareesh et al. established a beneficial effect of walnut consumption in ameliorating the symptoms associated with Alzheimer’s and Parkinson’s disease. In brain tissue, walnuts have a specific protective effect against oxidative stress, neuroinflammation and cellular damage. This is due to their high flavonoid, ellagic acid, vitamin E, selenium and polyunsaturated fat content. The authors describe cognitive decline as a symptom that develops later in life and as such suggest early and long-term dietary inclusion of walnuts to help support brain health.
A noteworthy finding is that the most beneficial health outcomes seem to occur in elderly populations, according to the data. For example, a Spanish study with 522 subjects with an average age of 74 years found that supplementation of 30g of nuts per day (of which 15g were walnuts) saw significant improvements in cognitive function and memory compared to the control group on a low fat diet.
Another compelling study spanning over two decades, known as the National Health and Nutrition Examination Survey found that cognition scores between women who consumed five or more serves of walnuts per week compared to those who didn’t, were vastly different. In fact the results showed it was equal to two years of neurodegenerative changes and ageing.
Melatonin is commonly known as the master neurotransmitter responsible for sleep-wake cycle regulation in the brain. It also has anti-inflammatory and anti-cancer properties and is thought by researchers to be generally neuroprotective. What many people may not know is that melatonin as an amino acid occurs in many food sources, including plants and is known as phytomelatonin. This compound is found in walnuts along with alpha-linolenic acid, which leads experts to believe walnuts could be a natural antidepressant. This was confirmed in a modest 6-week trial of walnut supplementation in a group of healthy young men. Another in vivo study confirmed the activity of walnut flour on breast cancer cells, and demonstrated that the phytomelatonin constituent of walnuts has immunomodulatory and anti-tumour activities.
Cardiovascular Health, Cholesterol & Weight Management
In the early 90’s clinical trials were actively assessing the role of walnuts as a healthful addition to a standard Western diet. At the time data was emerging in support of the inclusion of healthy fats from plants and nuts in an effort to improve cardiovascular health, weight management and cholesterol levels. These early studies demonstrated substantial improvements in cholesterol profiles, more than what was currently being recommended as part of a cholesterol-lowering diet.
Another study of elderly participants with a mean age of 69 assessed the influence of walnut supplementation on cholesterol levels. Over 600 participants completed the study lasting 2 years and the walnut group saw reduced triglyceride levels, thereby also improving cholesterol levels and global cardiovascular health.
Alpha-linolenic acid (ALA), which is the primary polyunsaturated fatty acid in walnuts, is converted in the body to EPA and DHA. Well-known for reducing inflammation in the brain, soft tissue and joints, ALA is also associated with lower heart attack rates and supports normal heart rhythms. It appears from the research that phytosterols found in walnuts also have a cholesterol-lowering effect. Phytosterols, which are found in olives and avocadoes, are a compound that behaves similarly to cholesterol in the body. Research shows that phytosterols are protective in human health because they compete with other ‘bad’ types of cholesterol for absorption in the intestine, which results in an overall healthier cholesterol profile.
An old belief, which thankfully has shifted in the past couple of decades, is that high fat diets are detrimental to health and consuming foods high in fat will cause weight gain. As nuts are full of natural fats, a few studies have examined walnut consumption and weight gain. Interestingly, a walnut-rich diet can actually promote weight loss, and improve BMI scores as was discovered in a randomized trial of one hundred overweight and obese men. Because walnuts are also well established as being cardioprotective, they make a healthful addition to the diet in addressing all metabolic disease risk factors.
Greens & Walnut Pesto
¼ to ½ cup olive oil
1 large bunch each of basil, parsley and spinach (about 2 cups each)
¼ cup walnuts
60g parmesan cheese
1 clove garlic
Salt and pepper to taste
- Place olive oil, basil, parsley, spinach, walnuts, parmesan, garlic and juice of ½ lemon into food processor
- Pulse until combined and coarse pesto consistency achieved
- Add salt and pepper
- Taste and add more lemon if needed
- Enjoy immediately or store in refrigerator for a week.
Vanilla Toasted Walnuts
(recipe adapted from Elana’s Pantry)
- 2 cups raw walnuts
- 1 tablespoon olive oil
- 2 tablespoons maple syrup
- ¼ tsp. sea salt
- 1 vanilla bean, scraped or 1 heaped tsp. vanilla extract
- ½ tsp. cinnamon
- Place walnuts and oil in a large pan, turn heat to medium-high
- Once sizzling turn heat to low and continue to toast until fragrant, turning occasionally
- Add maple syrup, cook for a further minute and add salt
- Turn heat off and mix in vanilla and cinnamon
- Transfer to bowl and enjoy
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