TL;DR
A post hoc analysis of a randomized trial found that older adults assigned to eat walnuts daily had about 6% higher total IgG levels than controls after two years. The study did not show that this change improved immunity or heart health, and walnut intake did not significantly affect several other measured immune markers.
A post hoc analysis of a two-year randomized trial found that older adults assigned to eat walnuts daily had about 6% higher total IgG levels than participants assigned to avoid walnuts. The study, published in JACC Advances, measured immune biomarkers but did not establish that the difference improves health or prevents cardiovascular disease.
The analysis used data from the Walnuts and Healthy Aging (WAHA) trial, which enrolled 708 cognitively healthy adults aged 63 to 79 in the United States and Spain. Participants were assigned either to a walnut-based diet or to a diet excluding walnuts for two years. The walnut group was asked to eat 30 to 60 grams daily, roughly 15% of daily energy intake.
For this later analysis, researchers tested blood samples collected at the start and after two years from 474 participants: 240 in the walnut group and 234 controls. They measured total immunoglobulin G (IgG) and immunoglobulin M (IgM), antibodies targeting modified LDL, and levels of malondialdehyde-modified LDL (MDA-LDL). The original WAHA trial focused on cognition and retinal health, rather than these immune outcomes.
The approximately 6% higher total IgG result was observed across the two study locations after adjustments for baseline levels and other factors. The difference was larger in the U.S. participants, at 11%, while researchers found no statistically significant intervention effect in Spain. Walnut assignment did not significantly affect total IgM, MDA-LDL, or the measured MDA-LDL-specific IgG and IgM antibodies compared with the control diet.
What the IgG Difference Can Show
IgG is a class of antibody involved in the body’s humoral immune response. A measured increase in total IgG is a change in a blood biomarker; by itself, it does not show that participants had better protection against infection, a stronger overall immune system, or fewer heart problems. The researchers described the clinical implications as uncertain.
The question matters because atherosclerosis involves plaque formation and chronic inflammation, and immune responses can play a part in disease processes. But this analysis did not demonstrate that walnuts changed plaque, prevented cardiovascular events, or improved a clinical outcome. It also did not find a significant effect on the specific antibodies against MDA-LDL that the investigators examined. The result is a lead for further research, not evidence that eating walnuts is an immune treatment.
How the WAHA Analysis Was Conducted
Participants were recruited between May 2012 and May 2014 and followed for two years. People who already ate more than two servings of tree nuts weekly were excluded, as were people regularly using certain soy lecithin, fish oil, or flaxseed oil supplements. Follow-up visits took place every two months to monitor weight, tolerance, diet compliance, and medication use.
The researchers used laboratory assays to assess blood samples and statistical models adjusted for factors including age, sex, smoking, study center, cholesterol, body mass index, hypertension, and diabetes. Among Spanish participants, red blood cell alpha-linolenic acid—a marker used to assess adherence—increased substantially in the walnut group and fell in controls. The report also found that baseline total IgG and IgM levels were lower among U.S. participants than Spanish participants, highlighting differences between the two centers.
The findings should be read alongside earlier research cited by the authors. Some studies have associated higher total IgG or particular antibodies against oxidized LDL with cardiovascular outcomes, but results for MDA-LDL-specific IgG have been inconsistent. Those associations do not establish that raising IgG through diet changes a person’s risk.
“The clinical implications remain uncertain.”
— The study authors, as summarized in the report
What the Biomarker Cannot Establish
The analysis does not show why total IgG was higher in the walnut group or whether the difference has any effect on health. It reports no evidence that the change translated into fewer infections, improved immune function, or fewer cardiovascular events. The researchers also found no statistically significant effect in Spain, so the reason for the difference between the U.S. and Spanish results is unresolved.
The study measured these outcomes in a subset of the original trial, and the immune analysis was conducted after the main trial had been designed around other outcomes. Although the researchers adjusted for several factors and ran sensitivity analyses, those steps cannot answer every question about the result. The report does not establish whether the IgG difference persists beyond two years, how it relates to specific immune responses, or whether it would apply to other age groups and populations.
Questions for Future Walnut Studies
The findings point to a need for research that tests whether changes in IgG are reproducible and connected to outcomes people experience, rather than only laboratory measurements. Further studies could examine why the result differed by study location and whether changes in particular antibody responses accompany the increase in total IgG.
No follow-up study or new milestone is specified in the report. Until further evidence is available, the WAHA analysis supports a limited conclusion: walnut consumption was associated with higher total IgG in this trial, but the health significance has not been established.
Key Questions
What is IgG?
IgG is a type of antibody measured in the blood and part of the humoral immune response. The study measured total IgG; it did not show that a higher level meant participants were healthier or better protected.
How much higher was IgG in the walnut group?
Across both trial locations, total IgG was about 6% higher in the walnut group than in controls after two years, after statistical adjustment. The U.S. subgroup showed an 11% difference, while no statistically significant effect was detected in Spain.
Did the study show that walnuts prevent heart disease?
No. The analysis measured immune and related blood biomarkers and did not establish that walnuts prevented heart disease or reduced cardiovascular events.
Did walnuts change all the immune markers tested?
No significant intervention effect was found for total IgM, MDA-LDL, or the measured MDA-LDL-specific antibodies. Total IgG was the main marker that differed between the groups.
Does this mean people should eat walnuts to raise IgG?
The study does not establish that raising IgG is beneficial, and it was not a test of walnuts as a treatment. Its findings are limited to the trial participants and the biomarkers measured.
Source: news-medical.net
