Walnuts are wrinkly, bumpy, double lobed nuts of the Juglandaceae family. The edible kernels we know and love are technically fruits since they are formed within a fleshy green drupe that encloses the hard nut shell. Mild and smooth in taste and texture, walnuts can be enjoyed raw, toasted, and sprinkled atop many dishes and desserts to add some buttery crunch.
Walnuts also happen to be among the world’s healthiest foods.
1. Walnuts Are Incredibly Nutritious
Walnuts are an excellent source of healthy fats, protein, fiber, and minerals:
|Per Cup of Walnuts, Chopped||% of DV|
|Vitamin C||1.5 mg||3%|
|Vitamin E||0.8 mg||4%|
|Vitamin K||3.2 mcg||4%|
|Vitamin B6||0.6 mg||31%|
|Pantothenic Acid||0.7 mg||7%|
2. Walnuts Are Rich In Antioxidants
In addition to its vitamin C and E content, walnuts provide other important antioxidants.
According to a study published in Food Chemistry, walnut kernels are composed of at least seven phenolic compounds that display strong antioxidant activity. Of these, four were found to display higher free radical scavenging activity than Trolox, a positive control with a similar biochemical structure to vitamin E.
Although it is usually removed before consumption, the thin, papery skin that clings to the kernel of a shelled walnut demonstrates a much more potent antioxidant status than the nut itself. In a 2008 analysis comparing walnut skins (also referred to as hulls or pellicles) with dehulled walnut kernel flour, the skins displayed a higher margin of antioxidant activity. For example, the hulls of the Criolla variety of walnut had an antioxidant activity score of 286, but when the same variety was de-skinned and rendered into a flour, its antioxidant activity was reduced to 15.1.
The antioxidant content of walnuts have proved to be readily bioavailable as well. Just one hour after consuming walnuts, healthy volunteers had significantly higher concentrations of ellagitannins in their blood and urine per a 2014 study.
3. Walnuts Are A Good Source Of Omega-3 Fatty Acids
Omega-3 fatty acids are polyunsaturated fats that provide a myriad of health benefits. These dietary fats have been associated with the prevention of cardiovascular disease, preserving cognitive function, and boosting fetal development.
Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are two types of omega-3 fats that are derived only from marine sources such as seafood, fermented cod liver oil, or krill oil. A third type of omega-3 fatty acid, alpha-linolenic acid (ALA), is found only in plant sources like flaxseed, soy, canola, and walnuts.
ALA is a precursor to EPA and DHA. When we consume foods high in ALA, our bodies convert it into EPA and DHA.
While most research on omega-3 fats have focused on EPA and DHA, some studies have investigated the health effects of consuming foods high in ALA. In a 5-year study involving 605 patients, a high ALA diet reduced the incidence of death from cardiovascular disease and myocardial infarction compared to a standard diet. A 2009 review of the cardiovascular effects of consuming ALA rich flaxseed found that it is cardio protective and reduces many of the risk factors associated with heart disease. In the case of eating walnuts specifically, a small 2006 study found that eating just four walnuts per day for three weeks boosted ALA content in blood and significantly increased EPA and DHA levels as compared to baseline levels.
4. Walnuts Promote A Healthy Gut
The microbiome of the human gut contains tens of trillions of microorganisms, with at least 1,000 distinct species of bacteria and more than 3 million genes. Gut flora is found in the stomach and intestines and its content is influenced by your age and geographical location. Each individual’s gut bacteria is as unique as a fingerprint.
An imbalance of gut flora plays a role in many disparate diseases – from ulcers to cancer to psychiatric disorders – so keeping your digestive system happy is well advised.
Although not a prebiotic by definition, walnuts may act as a prebiotic by selectively promoting and increasing the activity and volume of good bacteria in the gut. Published in Nutrients, the 2018 study found that consuming 43 grams of walnuts each day for eight weeks significantly changes the composition and diversity in the gut by enhancing probiotic species. Eating walnuts also increased intestinal butyrate, a short chain fatty acid that regulates gene expression; it has been associated with preventing inflammation, insulin resistance, strokes, and colon cancer.
5. Walnuts For Appetite & Weight Control
Like all nuts, walnuts are dense in calories. And yet, in numerous studies investigating the health benefits of walnuts, participants who added them to their existing diet did not gain weight – even while the number of calories consumed increased.
To better understand this disparity, researchers recruited 90 healthy individuals for a year long study. Published in British Journal of Nutrition, the crossover trial involved volunteers consuming 28 to 56 grams of walnuts each day for six months and then switching to their regular diets (sans walnuts) for another six months as control. The participants consumed 35 g of walnuts per day on average, which should translate to a theoretical weight gain of more than 11 pounds over six months. But the results of the study showed that changes to body weight, fat mass, percentage of body fat, fat-free mass, and total body water were minimal and insignificant.
In another study investigating the effects of a walnut rich diet on the metabolic parameters of type 2 diabetes patients, subjects who ate 30 grams of walnuts per day for one year experienced 2 to 4 pounds of weight loss (despite being on weight maintenance diets) and improved insulin, cholesterol, and fasting glucose levels.
There are several mechanisms at work that might explain these counterintuitive findings. Walnuts are high in fiber, a carbohydrate that passes through the body undigested. High fiber foods tend to produce feelings of satiety. Walnuts also have a good polyunsaturated to saturated fats ratio, which can kick off diet induced thermogenesis, a natural process that helps boost the metabolism, speeds up fat burning, and suppresses appetite. Although walnuts are high in total fat, eating them whole leads to poor fat absorption, and scientists have found that people who eat nuts tend to have a higher amount of fat in their stools. Also, walnuts may not even be as calorie dense we think.
6. Walnuts Boost Brainpower
Although all types of nuts are great brain food, walnuts appear to have an edge over the rest.
The link between walnuts and better brain function was gleaned from data produced in NHANES, a large scale survey of over 20,000 American adults. Published in the Journal of Nutrition, Health and Aging, those who consumed 10 grams or more of walnuts each day had significantly faster response time, information processing speed, and higher scores for memory, concentration, and motor control than those who never ate nuts. The walnut group’s scores were slightly better than those who occasionally ate walnuts along with other kinds of nuts.
Because walnuts are enriched with antioxidants, polyunsaturated fatty acids, and anti-inflammatory phytochemicals, eating them on the regular also has a neuroprotective effect by slowing brain aging and lowering the risk of chronic neurodegenerative disorders later in life.
7. Walnuts Are Chemoprotective
The combination of phytochemicals in walnuts – and in particular ellagitannins – may provide protection against several types of cancer.
In a 2015 study, women who ate a minimum of 28 grams of walnuts, almonds, or peanuts at least once a week had a 2 to 3 times lower risk of developing breast cancer.
In a test tube study on prostate cancer cell cultures, the ellagitannins in walnuts were found to suppress and inhibit the expression of genes associated with prostate cancer and induced apoptosis (or cell death) of certain prostate cell lines.
Walnuts have also been shown to protect against colon cancers in a 2016 animal study. By eating a diet that included 7% walnuts, tumors in mice were reduced more than twofold.
8. Walnuts Improve Male Fertility
The Western diet is associated with high intakes of fried foods, high fat dairy, salt, processed meat, butter, refined grains, and high fructose corn syrup. Although prenatal care is typically focused on maternal nutrition to maximize reproductive success, far less emphasis is placed on essential nutrients for male fertility.
Selenium, zinc, folate, vitamins C and E, and polyunsaturated fatty acids are some of the nutrients believed to be beneficial for sperm health and mobility. Because walnuts are rich in many of these elements, researchers investigated how eating walnuts might affect sperm vitality in a 2012 study. Recruiting 117 healthy men who routinely consume a Western-style diet, half were instructed to include 75 grams of walnuts each day for 12 weeks. Compared to the control group that experienced no changes in sperm quality, the walnut group had improved semen parameters, including increased fatty acid profiles, sex hormones, mobility, and structure.