One of the first definitions on healthy aging defined it as being “…free of disease; can function at a high physical and cognitive level, are socially engaged, and are productive.”1
Although the latest Centers for Disease Control and Prevention data show a decrease of 1.8 years from 2019, Americans are historically living longer than they ever have, with life expectancy now at 77 years in 2020.2 Interestingly, while research and medicine have been successful in increasing lifespan (i.e., how long we live), there are fewer advances in determining ways to make those extra years healthy (i.e., quality of life lived healthy) – this is known as health span.3
It’s critical to better understand how health and quality of life factor into aging in terms of how older age can be accompanied by good health and well-being, as opposed to extending years with sickness and frailty.
Can dietary recommendations be developed that are aimed at improving health span, and reducing the risk or progression of age-related adverse health outcomes, such as cognitive impairment or sarcopenia?
Let’s look at the latest research.
USING WHOLE FOODS: FOCUS ON NUTS
Investigators are looking at specific whole foods to learn how and why they may play a role in an eating pattern that supports healthy aging. Policy makers are also supporting momentum behind the “food as medicine” approach to enhance overall health and reduce diet-related diseases as we age.4,5
Nuts
The numerous bioactive compounds in nuts, such as proteins, monounsaturated fatty acids, polyunsaturated fatty acids, vitamins, minerals, fiber, polyphenols, and phytosterols, are gaining attention from researchers who are studying how to improve health span.6 Scientists are interested to reveal if these nutrients contribute singularly or synergistically to the many positive health outcomes documented below. As a reference, when it comes to nuts like walnuts, the United States Department of Agriculture (USDA) defines a serving as one ounce, ¼ cup, or a handful of walnuts, while the United States Food and Drug Administration (FDA) Health Claim supports 1.5 ounces per day of walnuts as a serving to decrease risk of heart disease.
The FDA Health Claim notes that supportive but not conclusive research shows that eating 1.5 ounces of walnuts per day, as part of a low saturated fat and low cholesterol diet and not resulting in increased caloric intake, may reduce the risk of coronary heart disease.
One ounce of walnuts, for example, offers 18 grams of total fat, 2.5 grams of monounsaturated fat, 13 grams of polyunsaturated fat including 2.5 grams of alpha-linolenic acid (ALA) – the plant-based omega-3.
Investigators are also curious to determine if eating nuts can help with the preservation of physical and cognitive functions, the maintenance of high standards of life quality, and ultimately, independence into older adulthood. A growing body of evidence suggests that simple food-based strategies, such as increasing the intake of nuts in the diet, may positively improve the aging processes. Nuts may be an important part of the relationship between lifespan and health span.7
In 2020, an observational study focused on healthy aging in women in their late 50’s and early 60’s, found that participants who consumed at least two servings of walnuts per week had a greater likelihood of healthy aging compared to those who did not eat walnuts (P trend < 0.0001).8 After accounting for various factors that could impact health in older adults, such as education and physical activity, researchers found a significant association between total nut consumption (including walnuts, peanuts and other nuts, without peanut butter) and healthy aging (OR = 1.14, 95% CI 1.02–1.28, trend = 0.046). The link was also significant for walnuts alone (OR = 1.20, 95% CI 1.00–1.44 for ≥2 servings per week versus no intake, trend = 0.0001).
Researchers in this study suggest these observed associations between nuts, including walnuts, and healthy aging, could be due to their nutrient composition. Specifically, the researchers call attention to the vitamin and mineral content, unsaturated fatty acids, and bioactive phytochemicals found in nuts. In the case of walnuts, the high levels of ALA and other plant-based bioactive phytochemicals are thought to contribute to these results.
In this study, the researchers defined “healthy aging” across 4 health domains following survival beyond the age of 65. “Healthy” agers had no history of chronic diseases (history of 11 chronic diseases assessed), no reported memory impairment (7 questions on memory concerns), no physical disabilities (Medical Outcomes Study Short Form-36), and intact mental health (Geriatric Depression Scale with 15 items).
Limitations of this study include that participants were not assigned to eat walnuts or other foods, they were asked about their dietary choices. It is possible that subjects misreported their dietary intake since this information was collected by questionnaires. As an observational study, this does not prove cause and effect. However, this research sheds light on simple habits that can influence an individual’s health as one ages. It’s not yet known if adding walnuts to the diet of the general population will produce similar results.
In the Walnuts and Healthy Aging study (WAHA), a large, two-year randomized controlled trial examining whether walnuts contribute to healthy aging, researchers evaluated whether regular walnut consumption, regardless of a person’s diet or where they live, has beneficial effects on lipoproteins.9 They also looked at cognitive decline.10 This study was conducted from May 2012 to May 2016, and published in 2020-2021. It involved 708 participants between the ages of 63 and 79 (68% women) who were healthy, independent-living adults residing in Barcelona, Spain, and Loma Linda, California.
Participants were randomly divided into two groups: active intervention and control. Those allocated to the intervention group added about a half cup of walnuts to their usual daily diet ~15% energy, 1-2 ounces while participants in the control group did not eat any walnuts. Findings from these studies can be summarized as follows from the WAHA researchers:
- “The walnut diet significantly decreased (mg/dL) total cholesterol (mean –8.5 [95% CI, –11.2 to–5.4]), LDL-C (mean –4.3 [–6.6 to –1.6]), and intermediate-density lipoprotein cholesterol (–1.3 [–1.5 to–1.0]), corresponding to reductions of 4.4%, 3.6%, and 16.8% respectively.”9
- “Walnut supplementation for 2 years had no effect on cognition in healthy elders. However, brain fMRI and post hoc analyses by site suggest that walnuts might delay cognitive decline in subgroups at higher risk.”10
Because the participants of the WAHA study were older adults, these results cannot be applied to the general population and more work is needed in different research settings to confirm the study findings.
In another observational study published in 2021, researchers examined data from 67,014 women of the Nurses’ Health Study with an average age of 63.6 years and 26,326 men from the Health Professionals Follow-up Study aged 63.3 years in 1986 (the first cycle collected data of walnut consumption in both cohorts).11 Using models, which were adjusted for age and other confounding factors like smoking status, alcohol intake, physical activity, and family history of disease, researchers found that eating five or more servings of walnuts per week was associated with a 25% lower risk of dying from cardiovascular disease compared to non-consumer (HR: 0.75, 95% CI: 0.62, 0.92). Researchers also observed that those who consumed walnuts more than 5 servings/week could potentially gain 1.30 years of life expectancy (1.30 years in women and 1.26 years in men), compared to non-consumers.
Interestingly, the study authors found that even among participants with a suboptimal diet, as measured by a validated index based on foods and nutrients predictive of chronic disease risk, just a one-half serving per day increase in walnut consumption was associated with a reduced risk of total mortality (HR: 0.88, 95% CI, 0.81–0.95).
Participants were relatively healthy when they joined the studies (e.g., free of cancer, heart disease, and stroke) and were followed for about 20 years (1998-2018). Dietary intake was assessed every four years, and participants reported on their overall dietary intake – including how often they consumed walnuts, other tree nuts, and peanuts – as well as lifestyle factors like exercise and smoking status. Based on this data, the researchers were able to identify associations between walnut consumption at varying levels and different health indicators related to longevity. Researchers noted that every increase of 0.5 servings of walnut per day was linked with lower risk of death from heart diseases overall (HR: 0.86, 95% CI: 0.79, 0.94).
As a prospective observational study, these results do not prove cause and effect, but they do shed light on how walnuts may support an overall healthy lifestyle that promotes longevity and benefits health span. The food intake information was also self-reported, which could introduce measurement error. Residual confounding variables may also exist which could not be adequately controlled for in the study. The results from this study do not apply to the general population.
SPOTLIGHT ON WALNUTS, NEURODEGENERATIVE DISEASES, AND HEALTH SPAN
An accumulating body of scientific evidence suggests that how we eat is an important factor for overall brain health, including as it relates to neurodegenerative conditions, like Alzheimer’s disease, that affect health span into our older years. Ongoing research continues to examine whether eating certain foods, like walnuts, may be linked with:10, 12-20
Improved cognitive function and memory in groups at high risk for age-related cognitive impairment.
A reduced risk of other diseases, such as cardiovascular disease or type 2 diabetes, which are risk factors for the development of dementia.
A reduced risk of developing or delaying the onset and/or slowing the progression of Alzheimer’s disease (AD).
Researchers have started to use pre-clinical and human study designs to study the possible effects of eating walnuts on brain health.12-20 Because neurodegenerative conditions take many years to develop, using walnuts as a dietary strategy early and often during the course of life may be a simple, positive action that patients and clients interested in preserving health span can take.
Cells
Walnut oil has been found to protect brain cells when using an early model of AD.13
- Researchers specifically published a new 2022 study in the journal Nutrients13 where they exposed human brain cells in an isolated condition to roughly 10 micrograms/mL of walnut oil from five grams of California walnut powder that contained various fatty acid compounds including ALA.
- The study found that walnut oil protected cells from oxidative stress, enhanced brain cell function, and reduced the formation of markers of AD progression known as beta-amyloid.
- Cell studies are valuable for providing background information and can be used as a basis for additional research needed to determine the effects on humans. Results from studies done in cells cannot be applied to humans.
Animals
A 2018 study using a mouse model of early AD published in the Journal of Alzheimer’s Disease suggests that eating walnuts (equivalent to one ounce and 1.5 ounces of walnuts per day in humans) may reduce the risk, or delay the onset and progression, of AD by reducing oxidative stress and inflammation in mice.14
- Animal studies are valuable for providing background information and can be used as a basis for additional research needed to determine the effects on humans. Results from studies done in animals cannot be applied to humans.
Humans
Clinical studies in humans show eating walnuts may reduce oxidative stress, inflammation, and other risk factors for AD.12 Also, researchers have identified positive associations between walnut intake and cognitive function within a wide array of populations, including older adults who may be at higher risk for developing neuro-degenerative conditions.10,12,15-17 For example:
- An observational study suggests consuming walnuts may be associated with a lower prevalence and frequency of depression symptoms among American adults. After evaluating study participants for depression, researchers found depression scores were 26% lower for walnut consumers and 8% lower for consumers of other nuts, compared to those who did not consume nuts at all. In this study, researchers from UCLA looked at the relationship between self-reported walnut intake and self-reported depression scores in 26,656 U.S-based adults who participated in the National Health and Nutrition Examination Survey (NHANES) from 2005 to 2014, which draws from a large sampling of the U.S. population. Average intake among walnut consumers was approximately 24 grams or just under one quarter cup of walnuts per day (typical serving size is 28 grams/1 ounce).16
- In another study, researchers found that walnut consumption had a positive impact on mood in male participants. The research showed that non-depressed healthy, young males (ages 18-25) had a 27% reduction in overall mood disturbances after eating 2 ounces of walnuts every day for 8 weeks. While maintaining their typical diet, activities and lifestyle habits, 64 university students ate banana bread daily for approximately four months. Participants spent 8 weeks eating 3 slices of banana bread with 2 ounces of walnuts, and then crossed over to eat banana bread without walnuts for another 8 weeks. Finely ground walnuts were added to the batter so there were no noticeable differences between the two types of banana bread. At the onset and after each phase of the study, participants answered a common questionnaire (Profiles of Mood States (POMS)) about key mood domains such as tension, depression, anger, vigor, fatigue and confusion. No significant changes in mood were observed in females or when the data was analyzed with both genders included. The greatest change among men that contributed to the reduction in mood disturbances was a 31% decrease in the anger-hostility domain.17
- People eat walnuts as part of complex diets such as the Mediterranean diet (MD). Clinical and observational studies show that following the MD seems to be linked with age-related neuroprotection and possibly less risk of AD progression.18-20 Walnuts are a staple nut and important component of the MD.
- Further work is needed to improve the understanding of the complex pathways through which eating patterns that include walnuts can influence the brain or affect risk of or progression of neurodegenerative conditions. Observational studies cannot prove cause and effect. Findings in clinical studies are limited to the population who received the walnut intervention and cannot be extrapolated broadly to other groups.
- More observational studies and clinical trials in humans are needed to determine the optimal quantity of walnuts needed to contribute to brain health and/or affect progression of neurodegenerative conditions.
Walnuts appear to have a nutrient matrix that may work together to deliver beneficial effects in the context of neurodegenerative diseases.12 Specifically, walnuts have plant-based nutrients with antioxidant and anti-inflammatory properties, including polyphenols, melatonin, folate, vitamin E, selenium, and plant-based omega-3 fatty acids.21 The synergistic effects of whole foods, such as walnuts, on disease risk, has also been discussed at length previously by researchers in a scientific symposia format.22
HEALTHY DIETARY PATTERN RESEARCH
Over the course of 25 years, investigators have gone from looking at nutrients in isolation (vitamin E) to whole foods research (mushrooms or berries), to complex dietary patterns (Mediterranean style diet). Let’s look at three dietary patterns that are associated with healthy aging.
The Mediterranean-DASH Intervention for Neurodegenerative Delay or (MIND) diet has 15 components, including 10 brain-healthy food groups that you should eat daily, and five unhealthy groups (red meat, butter and stick margarine, cheese, pastries and sweets and fried or fast food) that you should limit. The MIND diet recommends whole grains, vegetables, beans, nuts, fruits, seafood, olive oil and red wine (if you prefer) every day. The MIND diet also recommends foods high in omega-3s, particularly nuts like walnuts with its high ALA content, that play particularly well within this dietary pattern. Since the diet was introduced in 2015, several studies have revealed that adherence to the MIND diet may be associated with a slower rate of cognitive decline.23
The Mediterranean diet (MD) is a primarily plant-based eating plan that includes daily intake of whole grains, olive oil, fruits, vegetables, beans and other legumes, nuts, herbs, and spices.24 Animal proteins are eaten in smaller quantities, with a recommendation of two servings per week of fish and seafood. Intake of dairy foods and eggs should be moderate with very little consumption of red meat and simple carbohydrates. Researchers have found that the MD may be linked with improved health span, as confirmed most recently by an observational study using 10 years of international data.25-27
PREDIMED (PREvención con DIeta MEDiterránea=Prevention with Mediterranean Diet) was a landmark study aimed at assessing the efficacy of the MD in the primary prevention of cardiovascular disease.28 Researchers examined whether a MD supplemented with extra-virgin olive oil or mixed tree nuts (50% walnuts, 25% almonds, and 25% hazelnuts), compared to a low-fat diet, could help reduce the risk of major cardiovascular events, including cardiovascular death, myocardial infarction (heart attack) and stroke. The study was a parallel group, multi-center, single-blind, randomized clinical trial that was conducted by 16 research groups and seven communities and supported by the Spanish Health Ministry.
Participants included 7,447 Spanish individuals (ages 55-80) at high risk of cardiovascular disease, but without symptoms at baseline, and were followed for a median of 4.8 years. Energy intake was not specifically restricted in any intervention group. Compared to the low-fat control diet, the MD enriched with extra-virgin olive oil or nuts saw lower incidence of major cardiovascular events (96 events MD w/ extra-virgin olive oil [3.8%], 83 events MD w/ nuts [3.4%], 109 events control group [4.4%]).
The study had some limitations, including the fact that participants lived in a Mediterranean country and were at high risk for cardiovascular disease. The seminal paper, “Primary Prevention of Cardiovascular Disease with a Mediterranean Diet,” was originally published in 2013,29 but was with- drawn from the New England Journal of Medicine (NEJM) in 2018 due to irregularities in the randomization procedures. The researchers reanalyzed the data and the updated manuscript was subsequently republished in the NEJM.28 There were no significant changes to the findings, despite the revised randomization methods.
More research is needed to clarify the health benefits of walnuts in other populations. Additionally, it is difficult to precisely define what part of the MD was associated with cardiovascular benefits.
Dietitians are Uniquely Positioned to Inform and Educate About Dietary Practices to Improve Health Span
Interpreting and applying nutrition research on health span can be challenging for policy makers, clinicians, the food industry, researchers, and consumers. Registered dietitians are uniquely positioned to be the gate-keepers of public opinion on the latest science covering the emerging role that food choice plays in improving health span across many populations.
Empowering consumers to adopt small lifestyle changes as it relates to food and drink choice early in the lifespan could help protect against diet-related disease risk, and ultimately poor health span, as they age.
Consider the following the next time discussions on health span arise in your practice:
- Advocate for simple, realistic, accessible, affordable, and enjoyable practices to increase the consumption of foods linked with improving health span, including but not limited to whole grains, legumes, fish, fruits, vegetables, and nuts, and reduce red and processed meats, sugar-sweetened beverages, and refined grains.30
- Express to patients and clients who may be hesitant about change, and who are younger or middle-aged, that it’s never too early to think about long-term health; small adjustments to their eating pattern and food choice now may make big differences later in life – even if they don’t see immediately gratifying results now.
- Address consumer fears and misperceptions about the fat content in nuts and poor health outcomes, specifically weight gain, that are causing some people to avoid eating them.31 In fact, a growing body of research highlights how plant-based foods, such as walnuts, may be beneficial for overall health, without contributing to weight gain, when part of an otherwise balanced eating pattern.32-37
- A recent study32 from the United States Department of Agriculture (USDA) even found that one serving of walnuts (1 ounce) may provide 146 calories, which is 39 calories less, or 21 percent fewer, than the 185 calories listed in the USDA Nutrient Database.21
- Explore more plant-forward dietary patterns such as the MD or Dietary Approaches to Stop Hypertension (DASH) with patients and clients, and consider working with them to include staple, culturally appropriate foods in these styles of eating.
- Registered dietitians must understand cultural differences in order to provide the best dietary recommendations to consumers regardless of race, origin, gender, age, religion, sexual orientation, social class, economic situation, and/or disability.
While the body of evidence on which foods – like nuts – and eating patterns are best suited for improving health span continues to grow, work with your patients or clients of all ages to have discussions on what improving health span means to them. Meet them where they are with realistic solutions for implementing the evidence-based dietary changes reviewed in this article.
