In a recent study published in Nutrients, researchers performed secondary analyses of the Walnuts and Healthy Aging study (WAHA) data, a two-year prospective, randomized controlled trial (RCT) carried out among the many 63 to 79-year-olds of Loma Linda University (LLU) in California, United States of America (USA) and Barcelona in Spain, between 2014 and 2016.

Study: Effect of Walnut Supplementation on Dietary Polyphenol Intake and Urinary Polyphenol Excretion within the Walnuts and Healthy Aging Study. Image Credit: Krasula/Shutterstock

The parent study examined the effect of each day dietary walnut supplementation of 30 to 60 grams/day on the aging outcomes in comparison with a walnut-free customary eating regimen. Nonetheless, in the current secondary data analyses, researchers used data from LLU participants only. They examined the results of dietary supplementation with walnuts at 15% of energy, i.e., the consumption of 30 to 60 grams of walnuts day-after-day.

Background

Dietary polyphenols are excellent antioxidants and anti inflammatory phytochemicals that supply multiple health advantages. For example, they increase high-density lipoprotein (HDL) and lower low-density lipoprotein (LDL) within the blood (or plasma) lipids, modify inflammation and endothelial dysfunctions, and increase antioxidant defenses, thus, reducing the danger of cardiovascular diseases (CVDs).

Among the many nuts, walnuts contain the very best concentrations of polyphenols and have a positive nutrient and fatty acid profile. Chromatography and mass spectrometry have identified that the majority polyphenols reside within the seed coat or pellicle of the edible walnut kernel, averaging 2,500 gallic acid equivalent (GAE) per 100 grams. Walnuts increase the concentration of plasma polyphenols inside half-hour of ingestion.

Concerning the study

In the current study, researchers first performed nutrient evaluation using the Nutrition Data System for Research, for which trained research dietitians obtained 24-hour dietary recall data via telephonic conversations or face-to-face interviews from all eligible participants. Next, they conducted these interviews over two years at various intervals to capture differences due to the season of food intake wherein they noted data on the food, beverages, and dietary supplements consumed by these individuals previously 24 hours.

Further, the team used the Phenol-Explorer database to estimate the polyphenol content of consumed foods and beverages from 24-hour dietary recall data. The rapid Folin–Ciocalteu (F–C) and chromatographic methods helped them estimate cumulative polyphenol content and polyphenol subclasses, respectively.

Polyphenol subclasses comprised phenolics; flavonoids consisted of flavonols, flavones, and anthocyanins; moreover, there have been the subclass lignans. The team entered how consumed foods contributed to all subclasses into the dietary database to match food composition data and compute the intake of aggregate dietary polyphenols and phenol subclasses.

Moreover, the team used spot urine samples of the WAHA participants to estimate the mixture urinary polyphenol concentrations in mg GAE/L. Within the second yr of the study, they adjusted for urine dilution resulting from creatinine concentration.

Results

From 356 LLU participants, the current secondary analyses used only 300 subjects. Each walnut-consuming and control groups had more women participants. In 1242 sessions, research dieticians collected five 24-h dietary recalls from most participants.

They noted that the walnut group had higher total fat, energy, and dietary fiber intake than the control group over the two-year study period. Accordingly, the mixture polyphenol intake within the walnut group (resulting from mean walnut consumption) was higher than the control group (632 vs. 40 mg/d). Walnut consumption also markedly contributed to more aggregate polyphenols, flavanols, flavonoids, and phenolic acids but not lignans. Thus, each study groups had comparable lignan intake.

In comparison with the baseline, the polyphenols urinary excretion within the walnut group approached statistical significance only in the primary yr (p-value 0.066). Nonetheless, within the control group, the values remained comparable in any respect time points, indicating no significant inter-group variations throughout the two-year study duration.

The analyses of spot urine samples didn’t show any correlation between dietary polyphenol consumption (via walnuts) and urinary polyphenol concentrations but an inverse correlation with flavonoid intake. The estimation method (the F-C assay) or the short half-life of bioavailable polyphenols and their metabolites could have caused this.

Around 5 to 10% of the entire dietary polyphenols reach the small intestine and are absorbed there resulting from their structural complexity and solubility. For the reason that gut also absorbs and eliminates some polyphenols, it explains their reduced urinary excretion.

Walnuts are wealthy in ellagitannins which hydrolyzes to ellagic acid, upon which the gut microbiota acts to provide urolithins. These are excreted primarily via urine and will function precious biomarkers of walnut consumption. Yet, future studies should utilize 24-h urine collection following the walnut consumption to capture most polyphenols within the urine samples.

Conclusions

The study evaluation showed that a single food, i.e., walnuts, increased the entire dietary polyphenols and their subclasses (except lignans) in healthy older adults. These individuals also showed higher energy, total fat, fiber, and unsaturated fatty acid intake. Thus, including nuts, equivalent to walnuts, in each day eating regimen could have significant health advantages. Nuts protect from age-related chronic illnesses, like CVDs and neurological disorders. Since additionally they have high amounts of polyphenols, they might synergistically reduce the disease risk.