Eating walnuts may reinforce positive health benefits including better diet quality and likelihood to be more active.

Researchers who reviewed 20 years of diet history and 30 years of physical and clinical measurements have found participants who ate walnuts early on in life showed a greater likelihood for being more physically active, having a higher quality diet, and experiencing a better heart disease risk profile as they aged into middle adulthood.

These  findings come from the Coronary Artery Risk Development in Young Adults Study (CARDIA),¹ a long-term and ongoing study that is supported by the National Heart, Lung, and Blood Institute of the National Institutes of Health and aimed at examining the development of heart disease risk factors over time.

This study is one of the longest to suggest that the simple act of adding a handful of walnuts into the diet often could act as a bridge to other health-promoting lifestyle habits later in life.

The findings also reinforce that walnuts might be an easy and accessible food choice to improve a variety of heart disease risk factors when eaten in young to middle adulthood.

In this recent study published in Nutrition, Metabolism, & Cardiovascular Diseases,² University of Minnesota School of Public Health researchers note that a possible explanation for the results could be due to the unique combination of nutrients found in walnuts and their effect on health outcomes.

Walnuts are the only tree nut to contain significant amounts of the plant-based essential omega-3 alpha-linolenic acid (ALA) (2.7g/30g), which research shows may play a role in heart health, brain health and healthy aging.^{^,3,4}.  Whilst also containing 4.4g of protein and are a source of fibre (1.4g) per 30g (a handful). Walnuts are a good source of (antioxidants) copper and vitamin E and micronutrients magnesium, vitamin B6, folate and thiamin (vitamin B1) and a source of (antioxidant) zinc, pantothenic acid (vitamin B5) and minerals iron and potassium.

According to Professor of Epidemiology and Community Health at the University of Minnesota School of Public Health and Lead Researcher on CARDIA, Lyn M. Steffen, PhD, MPH, RD, “Walnut eaters seem to have a unique body phenotype that carries with it other positive impacts on health like better diet quality, especially when they start eating walnuts from young into middle adulthood – as risk of chronic diseases like heart disease, obesity, and diabetes elevates.”

Study Overview

 In this observational, longitudinal study, partially supported by the California Walnut Commission, diet and health information was collected and analysed from 3,023 otherwise healthy black and white men and women aged 18-30 at one of four field centers located in Birmingham, AL, Chicago, IL, Minneapolis, MN, and Oakland, CA, when the CARDIA study began in 1985-86. Self-reported diet history was taken at three times throughout the study: baseline, year seven, and year 20. Physical and clinical measurements were taken at multiple exams spanning 30 years.

Diet history was categorised into “walnut consumers,” “other nut consumers,” or “no nut consumers,” and assessed for relationships among heart disease risk factors, including dietary intake, smoking, body composition, blood pressure, plasma lipids (e.g., triglycerides), fasting blood glucose, and insulin concentrations in 352 walnut consumers, 2,494 other nut consumers, and 177 no nut consumers.

Average intake of walnuts during the study was about 21g /day, and intake of nuts among other nut consumers was about 42.5g./day.

“There was a good degree of diversity in terms of the research field locations geographically speaking and the population studied,” said Steffen. “Following these black and white women and men for 30 years provides an unparalleled window of study into how lifestyle decisions made in free-living environments in young adulthood can affect health in middle-age,” adds Steffen.

 Study Results At A Glance

 Overall, the researchers reported the following results:

• Physical and Clinical Indicators of Heart Disease Risk After 30 Years:
  • Walnut consumers had higher self-reported physical activity scores than other nut and no nut consumers.
  • Compared to other nut consumers, eating walnuts was linked with a better heart disease risk profile:
    • Lower body mass index
    • Lower waist circumference
    • Lower blood pressure
    • Lower blood triglyceride levels
  • Eating walnuts was associated with less weight gain over the study period, and fewer participants who ate walnuts were classified as people with obesity compared to other nut and no nut consumers.
  • Compared to no nut consumers, walnut consumers had significantly lower fasting blood glucose concentrations while other nut consumers had higher LDL-cholesterol.
• Markers of Diet Quality After 20 Years:
  • Including walnuts in the diet during young adulthood was favorably linked with a higher total diet quality score (Healthy Eating Index 2015) when compared to other and no nut consumers.
  • Compared to other nut or no nut consumers, people who ate walnuts had the following self-reported daily dietary intakes, including a significant relationship with higher intakes of several under consumed nutrients and food groups of public health importance as outlined in the 2020-2025 Dietary Guidelines for Americans:^5*

“Nut consumers showed an advantage in relation to diet quality, but walnut consumers appear to have a better heart disease risk factor profile than the other groups, even after accounting for overall diet quality,” said Steffen. “The surprising, healthy shifts in overall dietary pattern of walnut consumers suggests walnuts may act as a bridge or ‘carrier food’ for helping people form healthy nutrition and lifestyle habits throughout life.”

While these results are positive and confirm earlier work from the CARDIA study on the health benefits of walnut intake,¹ randomised controlled clinical trials should be done in other populations and settings to confirm the observations in the current study. Observational studies cannot support cause and effect conclusions.

Additionally, some of the outcomes for heart disease risk factors relating to cholesterol and lipids in the current study are inconsistent with previous randomized controlled trials.^6,7 This could be related to differences in study design, including duration of the intervention (e.g., several months to 30 years) or amount of nut intake. Last, the researchers did not isolate other specific nuts in their database, so findings cannot indicate the benefit of other nuts.

This study is one of the longest to suggest that adding about a handful of walnuts to the diet every day and early on in life could be linked with benefits to overall diet quality as a heart-healthy “carrier food” that fits into any eating occasion.

References:

1. Steffen LM, Yi SY, Duprez D, Zhou X, Shikany JM, Jacobs DR Jr. Walnut consumption and cardiac phenotypes: The Coronary Artery Risk Development in Young Adults (CARDIA) study. Nutr Metab Cardiovasc Dis. 2021;31(1):95-101.
2. Yi SY, et al. Association of nut consumption with CVD risk factors in young to middle-aged adults: The Coronary Artery Risk Development in Young Adults (CARDIA) study [published online ahead of print July 30, 2022]. Nutrition, Metabolism and Cardiovascular Diseases. doi:10.1016/j.numecd.2022.07.013.
3. Sala-Vila A, et al. Impact of α-linolenic acid, the vegetable ω-3 fatty acid, on cardiovascular disease and cognition [published online ahead of print February 16, 2022]. Advances in Nutrition. doi:10.1093/advances/nmac016.
4. Sala-Vila A, et al. Effect of a 2-year diet intervention with walnuts on cognitive decline. The Walnuts And Healthy Aging (WAHA) study: A randomized controlled trial. Am J Clin Nut. 2020;111(3):590–600.
5. S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025. 9th Edition. December 2020. Available at DietaryGuidelines.gov.
6. Rajaram S, Cofán M, Sala-Vila A, et al. Effects of walnut consumption for 2 years on lipoprotein subclasses among healthy elders: findings from the WAHA Randomized Controlled Trial. Circulation. 2021;144(13):1083-1085.
7. Guasch-Ferré M, Li J, Hu FB, Salas-Salvadó J, Tobias DK. Effects of walnut consumption on blood lipids and other cardiovascular risk factors: an updated meta-analysis and systematic review of controlled trials. Am J Clin Nutr. 2018;108(1):174-187.

^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. (FDA) One ounce of walnuts 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 – the plant-based omega-3.

Peer-reviewed paper:

“Association of Nut Consumption with CVD risk factors in young to middle-aged adults: the Coronary Artery Risk Development in Young Adults (CARDIA) study”

| Nutrition, Metabolism, & Cardiovascular Diseases | DOI:10.1016/j.numecd.2022.07.013

So-Yun Yi, Lyn M. Steffen, Xia Zhou, James M. Shikany, David R. Jacobs, Jr

Funding Source: The Coronary Artery Risk Development in Young Adults Study (CARDIA) is supported by contracts HHSN268201800003I, HHSN268201800004I, HHSN268201800005I, HHSN268201800006I, and HHSN268201800007I from the National Heart, Lung, and Blood Institute (NHLBI).  Other funding was R01-HL-084099 from NHLBI (Dr. Myriam Fornage) and the California Walnut Commission (Dr. Lyn Steffen). This report was reviewed for scientific content by the CARDIA publications committee, on which there is an NIH representative. The California Walnut Commission had no role in writing or reviewing this paper.