Multiple new research abstracts suggest walnuts may have the potential to positively affect several important health factors. From their impact on colon cancer and certain aspects of cognitive aging, to their positive effect on both gut health and vascular health, the research findings presented at Experimental Biology 2015 (EB) detail our latest understanding of walnuts' inner workings. Running March 28 through April 1 in Boston, this annual meeting attracts an international audience of over 14,000 leading research scientists and exhibitors.
"These findings help advance the understanding of the many advantages of eating walnuts as part of a healthy diet, and add to the more than 159 published papers over 20 years that have shown how walnuts affect heart health, diabetes, cancer, cognition, fertility and weight management," said Dennis A. Balint, CEO, California Walnut Commission.
There are numerous possible active ingredients in walnuts that may be contributing factors in providing these health benefits. One component that differentiates walnuts is alpha-linolenic acid (ALA), the plant-based omega-3 fatty acid. Walnuts are the only nut that contain a significant amount of alpha-linolenic acid (ALA) with 2.5 grams per one ounce serving.
While scientific conclusions cannot yet be drawn from the abstracts presented at EB 2015, the following summaries share the latest findings:
- Colon Cancer: For the first time, researchers looked at whether components of walnuts have an effect on colon cancer cells. This cell study1 was conducted by the Department of Nutritional Science and Food Management at the Ewha Womans University in Korea, and showed that walnut extract significantly slowed the survival of the cancer stem cells as well as reduced the stemness of colon cancer stem cells. Given the results, researchers state there is reason to further explore the role of walnut consumption in colon cancer therapies targeting cancer stem cells.
- Gut Health: The gut microbiome is an ecosystem of bacteria that helps our bodies digest and use the food we eat; changes in the gut microbiome are linked to chronic diseases. A recent animal study2 conducted by the Department of Physiology School of Medicine at Louisiana State University Health Sciences Center looked at the effect of walnuts on two major gut bacteria communities. A diet with walnuts (approximately 2 ounce human diet equivalent) significantly altered the ratio of the two communities, therefore suggesting "a new mechanism, changing the gut microbial environment, by which walnuts may exert their beneficial health effects." As this study was performed on animals, however, findings cannot yet be implied for humans.
Aging/Brain Health: This animal study3 from the Human Nutrition Research Center on Aging at Tufts University looked at healthy rats, both young and old, and the impact of walnuts - a source of polyunsaturated fatty acids and nutrients such as folate, selenium, magnesium and polyphenols - on mechanisms in critical regions of the brain. Animals were segmented into three groups - one, the control group, who ate no walnuts at all (0%); a second that had 6% of their diet comprised of walnuts; and a third that had 9% of their diet comprised of walnuts (equivalent to one ounce and 1.5 ounces respectively in a human diet). The groups were monitored for ten weeks. According to the researchers, incorporating walnuts into one's diet may have protective effects on the aging brain. As this study was performed on animals, however, findings cannot yet be implied for humans.
Vascular Health: Microvascular function refers to the health of our smallest blood vessels, such as capillaries. A study4 from the Departments of Nutrition and Internal Medicine at the University of California, Davis of postmenopausal women with high cholesterol looked at the short-term impact of walnut consumption. The group that ate 40 grams, or 1.5 ounces, of walnuts per day saw improved vascular function. The study concludes this improvement is due to the effects from the walnut-derived fatty acids, alpha-linolenic acid (ALA) and linoleic acid (LA).
Findings like these pave the way for additional research aimed at understanding walnuts' role in disease prevention and management.
Walnuts May Improve Memory
This cross-sectional study is the first large representative analysis of walnut intake and cognitive function, and the only study to include all available cognitive data across multiple National Health and Nutrition Examination (NHANES) surveys. The NHANES surveys draw from a large sampling of the U.S. population, typically ages 1 to 90 years old. In this study, participants included adults ages 20-59 as well as 60 and over. Dr. Arab and co-researcher Dr. Alfonso Ang found that study participants with higher walnut consumption performed significantly better on a series of six cognitive tests.
Dr. Arab noted, “It is exciting to see the strength of the evidence from this analysis across the U.S. population supporting the previous results of animal studies (1,2,3) that have shown the neuroprotective benefit from eating walnuts; and it’s a realistic amount – less than a handful per day (13 grams).” The study adds to a growing body of research surrounding walnuts’ positive effect on reducing cognitive impairment and overall brain health, (4) which includes the possible beneficial effects of slowing or preventing the progression of Alzheimer’s disease in mouse models. (5)
As the baby boomer population grows older, conditions affecting memory such as Alzheimer’s and dementia will become a greater concern. According to a 2012 World Health Organization article, the estimated number of new cases of dementia each year worldwide is nearly 7.7 million, and the number of people living with dementia worldwide is estimated at 35.6 million. This number is predicted to double by 2030 and more than triple by 2050. (6)
There are numerous possible active ingredients in walnuts that may be contributing factors in protecting cognitive functions. This includes the high antioxidant content of walnuts (3.7 mmol/ounce), (7) the combination of numerous vitamins and minerals as well as the fact that they are the only nut that contain a significant source of alpha-linolenic acid (ALA) (2.5 grams per ounce), a plant-based omega-3 fatty acid with heart and brain-health benefits. (8)
“It isn’t every day that research results in such simple advice – eating a handful of walnuts daily as a snack, or as part of a meal, can help improve your cognitive health,” said Dr. Arab.
1. Derek R. Fisher, Shibu M. Poulose, Donna F. Bielinski, Barbara Shukitt-Hale, (2014) Serum metabolites from walnut-fed aged rats attenuate stress-induced neurotoxicity in BV-2 microglial cells. Nutritional Neuroscience 0 (0).
2. Poulose, Shibu M. et al. (2012) Walnut diet reduces accumulation of polyubiquitinated proteins and inflammation in the brain of aged rats. Journal of Nutritional Biochemistry, Volume 24, Issue 5, 912 – 919.
3. Lauren M. Willis, Barbara Shukitt-Hale, Vivian Cheng and James A. Joseph (2009). Dose-dependent effects of walnuts on motor and cognitive function in aged rats. British Journal of Nutrition, 101, pp 1140-1144.
4. Pribis P, Shukitt-Hale B (2014) Cognition: The New Frontier for Nuts and Berries. Am J Clin Nutr 100(suppl):347S-52S.
5. Muthaiyah B, Essa MM, Lee M, Chauhan V, Kaur K, Chauhan A, (2014) Dietary Supplementation of Walnuts Improves Memory Deficits and Learning Skills in Transgenic Mouse Model of Alzheimer’s Disease. J Alzheimers Dis 42(4):1397-1405.
6. 10 Facts on Dementia. (2012 April). Retrieved from http://www.who.int/features/factfiles/dementia/en/
7. Halvorsen BL, Carlsen MH, Phillips KM, Bohn SK, Holte K, Jacobs DR, Blomhoff R (2006) Content of redox-active compounds (ie, antioxidants) in foods consumed in the United States. Am J Clin Nutr 84, 95-135.
8. Fleming J, Kris-Etherton P, (2014) The Evidence for α-Linolenic Acid and Cardiovascular Disease Benefits: Comparisons with Eicosapentaenoic Acid and Docosahexaenoic Acid. Adv Nutr (5): 863S-876S
Walnuts in one's diet can protect against diabetes and heart disease
Medical researchers from the Yale-Griffin Prevention Research Center in Connecticut have found evidence suggestive that adding walnuts to one's diet can protect against diabetes and heart disease in at-risk individuals. Their original research article, "Effects of Walnuts on Endothelial Function in Overweight Adults with Visceral Obesity: A Randomized, Controlled, Crossover Trial," published September 2013 in the Journal of the American College of Nutrition, the Official Publication of the American College of Nutrition.
For the study, a sample of 46 adults aged 30-75 were selected. Participants had a Body Mass Index larger than 25, and a waist circumference exceeding 40 inches for men and 35 inches for women. They were also required to be non-smokers, and all exhibited one or more additional risk factors for metabolic syndrome, a precursor of diabetes and cardiovascular disease. The group was randomly assigned to two 8-week sequences of either a walnut-enriched ad libitum diet or an ad libitum diet without walnuts. Those chosen for the walnut diet were instructed to consume 56g of shelled, unroasted English walnuts per day as a snack or with a meal.
"We know that improving diets tends to be hard, but adding a single food is easy," explained Dr. David Katz, Director of the Yale-Griffin Prevention Research Center and lead author of the research team. "Our theory is that if a highly nutritious, satiating food like walnuts is added to the diet, there are dual benefits: the benefits of that nutrient rich addition and removal of the less nutritious foods."
The research found that daily intake of 56g of walnuts improves endothelial function in overweight adults with visceral adiposity. The addition of walnuts to the diet does not lead to weight gain. Further study on the topic is still suggested. "The primary outcome measure was the change in flow-mediated vasodilatation (FMD) of the brachial artery," wrote the research group. "Secondary measures included serum lipid panel, fasting glucose and insulin, Homeostasis Model Assessment-Insulin Resistance values, blood pressure, and anthropometric measures. FMD improved significantly from baseline when subjects consumed a walnut-enriched diet as compared with the control diet. Beneficial trends in systolic blood pressure reduction were seen, and maintenance of the baseline anthropometric values was also observed. Other measures were unaltered.
Whole walnuts and their extracted oil improve cardiovascular disease risk
Consumption of whole walnuts or their extracted oil can reduce cardiovascular risk through a mechanism other than simply lowering cholesterol, according to a team of Penn State, Tufts University and University of Pennsylvania researchers.
"We already know that eating walnuts in a heart-healthy diet can lower blood cholesterol levels," said Penny Kris-Etherton, Distinguished Professor of Nutrition, Penn State. "But, until now, we did not know what component of the walnut was providing this benefit. Now we understand additional ways in which whole walnuts and their oil components can improve heart health."
In a randomized-controlled trial, the researchers gave 15 participants with elevated blood cholesterol one of four treatments -- either 85 grams of whole walnuts, 6 grams of skin, 34 grams of defatted nutmeat, or 51 grams of oil. The team evaluated biochemical and physiological responses in the participants before the treatments were administered and again 30 minutes, one hour, two hours, four hours and six hours after administering the treatments. The researchers repeated this process for each of the remaining three treatments.
Results -- which appeared in the June 1 2013 issue of the Journal of Nutrition -- showed that a one-time consumption of the oil component in walnuts favorably affected vascular health. In addition, consumption of whole walnuts helped HDL -- good cholesterol -- perform more effectively in transporting and removing excess cholesterol from the body.
"Our study showed that the oil found in walnuts can maintain blood vessel function after a meal, which is very important given that blood vessel integrity is often compromised in individuals with cardiovascular disease," said Claire Berryman, graduate student in nutritional sciences, Penn State. "The walnut oil was particularly good at preserving the function of endothelial cells, which play an important role in cardiovascular health."
According to the researchers, walnuts contain alpha-linolenic acid, amma-tocopherol and phytosterols, which may explain the positive effects of the walnut oil treatment.
"Implications of this finding could mean improved dietary strategies to fight heart disease," said Berryman. "The science around HDL functionality is very new, so to see improvements in this outcome with the consumption of whole walnuts is promising and worth investigating further."
Further studies are needed to determine the mechanisms that account for cardiovascular disease risk reduction with walnut consumption, according to Kris-Etherton.
"Our study indicates that simple dietary changes, such as incorporating walnuts and/or their oil in a heart healthy diet, may reduce the risk of heart disease," she said.
Walnuts are top nut for heart-healthy antioxidants
A new scientific study positions walnuts in the No. 1 slot among a family of foods that lay claim to being among Mother Nature's most nearly perfect packaged foods: Tree and ground nuts. In a report at the 241st National Meeting & Exposition of the American Chemical Society, March, 2011, scientists presented an analysis showing that walnuts have a combination of more healthful antioxidants and higher quality antioxidants than any other nut.
"Walnuts rank above peanuts, almonds, pecans, pistachios and other nuts," said Joe Vinson, Ph.D., who did the analysis. "A handful of walnuts contains almost twice as much antioxidants as an equivalent amount of any other commonly consumed nut. But unfortunately, people don't eat a lot of them. This study suggests that consumers should eat more walnuts as part of a healthy diet."
Vinson noted that nuts in general have an unusual combination of nutritional benefits — in addition those antioxidants — wrapped into a convenient and inexpensive package. Nuts, for instance, contain plenty of high-quality protein that can substitute for meat; vitamins and minerals; dietary fiber; and are dairy- and gluten-free. Years of research by scientists around the world link regular consumption of small amounts of nuts or peanut butter with decreased risk of heart disease, certain kinds of cancer, gallstones, Type 2 diabetes, and other health problems.
Despite all the previous research, scientists until now had not compared both the amount and quality of antioxidants found in different nuts, Vinson said. He filled that knowledge gap by analyzing antioxidants in nine different types of nuts: walnuts, almonds, peanuts, pistachios, hazelnuts, Brazil nuts, cashews, macadamias, and pecans. Walnuts had the highest levels of antioxidants.
Vinson also found that the quality, or potency, of antioxidants present in walnuts was highest among the nuts. Antioxidants in walnuts were 2-15 times as potent as vitamin E, renowned for its powerful antioxidant effects that protect the body against damaging natural chemicals involved in causing disease.
"There's another advantage in choosing walnuts as a source of antioxidants," said Vinson, who is with the University of Scranton in Pennsylvania. "The heat from roasting nuts generally reduces the quality of the antioxidants. People usually eat walnuts raw or unroasted, and get the full effectiveness of those antioxidants."
If nuts are so healthful and nutritious, why don't people eat more? Vinson's research shows, for instance, that nuts account for barely 8 percent of the daily antioxidants in the average person's diet. Many people, he said, may not be aware that nuts are such a healthful food. Others may be concerned about gaining weight from a food so high in fat and calories. But he points out that nuts contain healthful polyunsaturated and monosaturated fats rather than artery-clogging saturated fat. As for the calories, eating nuts does not appear to cause weight gain and even makes people feel full and less likely to overeat. In a 2009 U. S. study, nut consumption was associated with a significantly lower risk of weight gain and obesity. Still, consumers should keep the portion size small. Vinson said it takes only about 7 walnuts a day, for instance, to get the potential health benefits uncovered in previous studies.
Walnuts, walnut oil, improve reaction to stress
A diet rich in walnuts and walnut oil may prepare the body to deal better with stress, according to a team of Penn State researchers who looked at how these foods, which contain polyunsaturated fats, influence blood pressure at rest and under stress.
Previous studies have shown that omega-3 fatty acids -- like the alpha linolenic acid found in walnuts and flax seeds -- can reduce low density lipoproteins (LDL) -- bad cholesterol. These foods may also reduce c-reactive protein and other markers of inflammation.
"People who show an exaggerated biological response to stress are at higher risk of heart disease," said Sheila G. West, associate professor of biobehavioral health. "We wanted to find out if omega 3-fatty acids from plant sources would blunt cardiovascular responses to stress."
The researchers studied 22 healthy adults with elevated LDL cholesterol. All meals and snacks were provided during three diet periods of six weeks each.
The researchers found that including walnuts and walnut oil in the diet lowered both resting blood pressure and blood pressure responses to stress in the laboratory. Participants gave a speech or immersed their foot in cold water as a stressor. Adding flax seed oil to the walnut diet did not further lower blood pressure. They report their findings in the current issue of the Journal of the American College of Nutrition.
"This is the first study to show that walnuts and walnut oil reduce blood pressure during stress," said West. "This is important because we can't avoid all of the stressors in our daily lives. This study shows that a dietary change could help our bodies better respond to stress."
A subset of the participants also underwent a vascular ultrasound in order to measure artery dilation. Results showed that adding flax oil to the walnut diet significantly improved this test of vascular health. The flax plus walnuts diet also lowered c-reactive protein, indicating an anti-inflammatory effect. According to West, that could also reduce risk of cardiovascular disease.
The researchers used a randomized, crossover study design. Tests were conducted at the end of each six-week diet, and every participant consumed each of the three diets in random order, with a one-week break between. Diets included an "average" American diet – a diet without nuts that reflects what the typical person in the U.S. consumes each day. The second diet included 1.3 ounces of walnuts and a tablespoon of walnut oil substituted for some of the fat and protein in the average American diet. The third diet included walnuts, walnut oil and 1.5 tablespoons of flaxseed oil. The three diets were matched for calories and were specifically designed for each participant so that no weight loss or gain occurred. The walnuts, walnut oil, and flax oil were either mixed into the food in such offerings as muffins or salad dressing or eaten as a snack. About 18 walnut halves or 9 walnuts make up the average serving used by the researchers.
After each diet, the participants underwent two stress tests. In the first test, they received a topic; and they were given two minutes to prepare a three-minute speech, which they presented while being videotaped. The second stressor was a standard physical test of stress consisting of submerging one foot in ice-cold water. Throughout these tests, the researchers took blood pressure readings from the participants.
Results showed that average diastolic blood pressure -- the "bottom number" or the pressure in the arteries when the heart is resting -- was significantly reduced during the diets containing walnuts and walnut oil.
Walnuts are a rich source of fiber, antioxidants, and unsaturated fatty acids, particularly alpha linolenic acid, an omega-3 fatty acid, and these compounds could be responsible for the beneficial effects on blood pressure. Flax oil is a more concentrated source of omega-3 fatty acids than walnut oil, but this study did not test whether flax oil alone could blunt cardiovascular responses to stress.
"These results are in agreement with several recent studies showing that walnuts can reduce cholesterol and blood pressure," noted West. "This work suggests that blood pressure is also reduced when a person is exposed to stress in their daily life."