Writing in the journal Nutrients, a team of Romanian researchers set out to examine the effects of four weeks of daily walnut intake on cardiometabolic parameters and anthropometric measurements in a group of men and women between the ages of 45 and 60.
“Research indicates that nut consumption has the potential to reduce cardiometabolic risk factors and the incidence of cardiovascular disease,” they wrote. “Walnut (Juglans regia L.), containing a balanced lipid profile and a significant concentration of bioactive antioxidant and anti-inflammatory compounds, has demonstrated potential health benefits.”
These bioactive compounds include unsaturated fatty acids, fiber, minerals (potassium, calcium and magnesium), vitamins (folate and vitamin E), phytosterols (campesterol, stigmasterol and β-sitosterol), and polyphenols (ellagic acid, gallic acid and hydrolyzable tannins).
Walnuts, MetS and VCAM-1
Metabolic syndrome (MetS) is a cluster of cardiometabolic risk (CMR) factors including abdominal obesity, high blood pressure, abnormal cholesterol levels and high blood sugar that significantly increase the likelihood of developing type 2 diabetes (T2D) and cardiovascular disease (CVD), as well as cognitive impairment and other disorders.
“The global incidence of MetS affects around 25% of the worldwide population, and this tendency closely aligns with the prevalence of obesity, the development of T2D and the aging process,” the researchers wrote. “However, the early diagnosis and treatment of dyslipidemia and hypertension have been shown to delay the onset of MetS, even with the rising prevalence of obesity.”
The researchers noted that the pathophysiology of metabolic syndrome is intricate and involves a complex relationship between various genetic and environmental factors, with chronic low-grade inflammation and neurohormonal activation playing significant roles in its development.
Here, the study looks at the vascular cellular adhesion molecule-1 (VCAM-1), a protein upregulated in CVD that is crucial to endothelial function—acting as a key player in inflammation and the regulation of leukocyte migration.
A previous meta-analysis by the same group showed that walnut-enriched diets significantly reduced triglycerides, total cholesterol and low-density lipoprotein cholesterol, but the researchers noted that the statistical analysis of the endothelial adhesion molecule VCAM-1 was impeded by the limited number of studies selected following the bias risk evaluation. There were also no significant changes noted in anthropometric measurements or glycemic parameters.
“The clinical data regarding the effects of walnut consumption on cardiometabolic risk parameters, especially on inflammatory and glycemic biomarkers, remain inconclusive in this age group,” the researchers wrote.
Study details
The randomized controlled cross-over trial recruited 22 middle-aged Caucasians who were randomly assigned to consume walnuts harvested from orchards in Satu Mare County in northwestern Romania per day or no walnuts as part of a controlled diet every day for four weeks.
“The experimental protocol of our research, involving the ingestion of 45 g of walnuts daily, is consistent with the Food and Drug Administration’s (FDA) dietary guidelines, which recommend the inclusion of 1.5 ounces (42–43 g) of walnuts in the daily diet of adults,” the researchers noted. “Nevertheless, this quantity differs from the general dietary guidelines, which recommend consuming 30 g of nuts daily as part of a diversified and balanced diet.”
Two 28-day intervention periods were separated by a one-month washout period, and the study assessed clinical and biochemical markers (soluble VCAM-1, lipid profiles, glucose metabolism, blood pressure and various anthropometric measurements) at the beginning and end of each intervention period. A total of 20 participants completed the trial.
“A statistically significant decrease was observed between the two groups in waist circumference, with its decline after daily consumption of walnuts, while the primary biomarker of interest, sVCAM-1, did not exhibit any significant differences among the other parameters that were examined,” the researchers reported. The study also observed a slight change in fasting blood glucose following walnut intake.
These findings align with results from a four-week crossover trial in 18 overweight hypercholesterolemic patients and those from a two-year parallel trial in 634 healthy participants—neither of which reported any significant changes in sVCAM levels, indicating that the effects of walnut consumption may vary based on individual health status or dietary context.
“In addition, the systematic review and meta-analysis by Hsu et al. found no significant decrease in VCAM-1 levels related to walnut consumption’s impact on markers of endothelial function in adults but indicated that walnuts may minimize the CVD risk by increasing flow-mediated dilation (FMD),” the researchers wrote.
In contrast, they also cited previous studies demonstrating that acute and chronic walnut intake can significantly reduce sVCAM levels and impact endothelial function to confer potential cardiovascular benefits.
“All the findings illustrate the intricacies of dietary interventions in cardiovascular health and highlight the necessity for additional research to elucidate the underlying mechanisms and validate these results across varied populations,” the study concluded, calling for longer-term interventions to investigate the benefits of daily walnut consumption and its impact on the onset and development of metabolic syndrome in this age group.
Source: Nutrients. doi: 10.3390/nu17132072 . “Benefits of Short-Term (4-Week) Daily Walnut Consumption in Middle-Aged Adults at Risk for Metabolic Syndrome: Outcomes of a Randomized Controlled Trial”. Authors: Letitia Mates et al.