Another Reason to Eat Your Vegetables — and Walnuts

By Jason Wermers, M.S. student in health science at the University of Maryland, Baltimore

The COVID-19 pandemic has put the spotlight on the human body’s immune system. When supercharged to fight an invader like the novel coronavirus, the immune system produces a strong inflammatory response. This doesn’t just harm the virus, it also harms the body; leading to fever, coughing, and other symptoms.

Additionally, consuming the wrong foods, such as processed sugars and omega 6 fatty acids, can also cause inflammation, but this can develop over many years, resulting in a much more subtle, but no less harmful, effect on the body.

Recently published longitudinal data show that a diet high in red or processed meat and sweetened beverages can prompt this more subtle, chronic inflammatory response which is associated with a greater risk for cardiovascular disease.

Conversely, the study reports that a diet high in green, leafy vegetables; dark yellow vegetables; whole grains; and fruits reduces the inflammatory response and is associated with a lower risk of cardiovascular disease.

A separate randomized controlled trial reports that adding walnuts can reduce the level of several inflammatory biomarkers after 2 years in healthy people ages 63 to 79 years.

Ramon Estruch, MD, PhD, of the Instituto de Salud Carlos III, Madrid, and the University of Barcelona, Spain, and colleagues explain in an editorial that these two studies, both published in the Nov. 10 issue of the Journal of the American College of Cardiology, “should provide the basis for designing healthier dietary patterns and upgrading their protective effects against [cardiovascular disease].”

3 long-term studies pooled

Jun Li, MD, PhD, of the Harvard T.H. Chan School of Public Health, and colleagues prospectively followed more than 200,000 health professionals who were included in three longitudinal studies and who did not have cardiovascular disease or cancer at baseline: Nurses’ Health Study (74,578 women, 1984-2016), Nurses’ Health Study II (91,656 women, 1991-2015), and Health Professionals Follow-Up Study (43,911 men, 1986-2016).

The study subjects participated in surveys of their dietary habits every 4 years. The investigators compared the subjects’ dietary patterns with the presence of inflammatory biomarkers in the blood and the development of cardiovascular disease.

The investigators’ analysis found that study participants who consumed a “pro-inflammatory” diet had a 38% higher risk of developing cardiovascular disease than those who consumed an “anti-inflammatory” diet.

Li and colleagues defined diets with “pro-inflammatory” potential as those high in red, processed, or organ meat, refined carbohydrates, or sweetened beverages. Diets with “anti-inflammatory” potential were defined as those high in green, leafy vegetables; dark yellow vegetables (including pumpkin, yellow peppers, and carrots); whole grains (such as wheat, oat and rye); fruits; tea; coffee; and wine.

Beneficial effects of walnuts

Montserrat Cofán, PhD, of Hospital Clinic, Barcelona, and colleagues conducted a randomized controlled trial of 708 people whom they termed “healthy elders” (ages 63 to 79 years) who were enrolled at two centers: Hospital Clinic, Barcelona, and Linda Loma University, California. The subjects were randomized to add 15% of their minimum daily energy requirement (between 30 and 60 grams, or about ⅓  to ⅔  of a cup) of walnuts per day to their diet or abstain from walnuts. All study participants were scheduled to visit dietitians once every 2 months for dietary consultation and to monitor their physical activity. The subjects’ inflammatory biomarkers were assessed at baseline and after 2 years of the diet.

In this study cohort, 66% of the participants were women, their mean age was 69 years, and nearly a third were taking statins for cholesterol control. After 2 years, 634 subjects were available for follow-up (about 90% of the original enrollment). The study found no change in weight and that participants complied well with the walnut diet. The people who consumed walnuts had significantly lower levels of 6 of 10 inflammatory biomarkers examined than subjects who abstained from walnuts.

These findings contradicted a 2017 meta-analysis of 25 randomized controlled trials that found no effect on inflammatory biomarkers with daily consumption of walnuts. However, Cofán and colleagues pointed out, most studies in that meta-analysis had small cohorts with short follow-up, whereas their study had a 2-year follow-up with a larger pool of participants.

Cofán and colleagues concluded that their study demonstrates the benefits of walnuts’ anti-inflammatory effects on lowering cardiovascular disease risk “beyond that of lipid lowering.”

Implications

In their editorial, Estruch and colleagues said the longitudinal data from Li and colleagues provide “comprehensive evidence” of the link between pro-inflammatory diets and cardiovascular disease risk. The study also confirms data from a 2018 meta-analysis of 14 studies, which found that a pro-inflammatory diet increased the risk of cardiovascular disease and cardiovascular-related death, Estruch and colleagues wrote.

The editorialists added that the study by Cofán and colleagues was the “largest and longest nut trial to date,” giving it more weight than the 2017 meta-analysis with which Cofán and colleagues contrasted their results. Furthermore, the new walnut study confirms findings from previous studies showing a reduction in cardiovascular disease risk and cholesterol levels from higher consumption of walnuts and other nuts.

“These protective effects could also be used for other highly prevalent chronic diseases in which chronic inflammation plays a relevant role, such as diabetes, cancer, depression, cognitive decline, and Alzheimer’s disease,” Estruch and colleagues conclude. “When choosing the foods in our diet, we should beware of their pro- and anti-inflammatory potential!”

Peer edited by Raj Trikha

Photo Credit: Narek75/Wikimedia Commons