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A post hoc analysis of the WAHA randomized trial found that older adults assigned to eat walnuts had about 6% higher total serum IgG than controls after two years. The study did not establish that the difference improves immunity or cardiovascular health, and it found no significant walnut-related changes in several other immune measures.
A secondary analysis of a two-year randomized trial found that older adults assigned to eat walnuts daily had total serum IgG levels about 6% higher than participants told to avoid walnuts. The finding concerns an immune-system biomarker, not a demonstrated health benefit: researchers said the clinical meaning of the difference remains uncertain.
The analysis, published in JACC Advances, 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 randomly assigned to a walnut-based diet or a diet excluding walnuts for two years. The intervention group was asked to eat 30 to 60 grams daily, accounting for roughly 15% of daily energy intake.
For this post hoc analysis, researchers measured immune and lipid-related markers in blood samples from 474 participants: 240 in the walnut group and 234 controls. Total IgG was about 6% higher in the walnut group after adjustment for baseline levels and other factors. In the US participants, the difference was about 11%; researchers did not detect a statistically significant intervention effect in Spain.
The reported difference was specific to total IgG. The analysis found no significant walnut-related effect on total IgM, MDA-LDL levels, or antibodies targeting MDA-LDL, a modified form of LDL cholesterol. Total IgG and IgM, as well as MDA-LDL-targeting IgM antibodies, declined over the two years in both groups. The study did not show that walnuts prevented illness or cardiovascular events.
What the IgG Difference Can Tell Us
IgG is a class of antibody involved in humoral immune responses. A higher total concentration indicates a difference in a blood measure, but it does not by itself show that a person is better protected from infection or has a healthier immune system. The trial analysis did not test whether the measured change affected participants’ ability to fight infections or their subsequent health.
The finding may be relevant to research on diet, immunity and atherosclerosis. Atherosclerosis involves plaque buildup and inflammation in blood vessels; modified LDL can prompt immune responses. But the walnut analysis did not find a change in MDA-LDL or the measured antibodies directed against it. The authors’ results therefore do not establish that the IgG difference lowers cardiovascular risk, and they do not support treating walnuts as a proven immune or heart-health intervention.
For readers, the distinction is between a biomarker association and a clinical outcome. The randomized diet assignment strengthens the comparison between groups, but this was a post hoc analysis of biomarkers from a trial originally designed to study cognitive function and retinal integrity. Further research would be needed to determine whether the IgG finding is reproducible and whether it matters for health.
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How the WAHA Analysis Was Conducted
The WAHA trial recruited participants between May 2012 and May 2014. People who ate more than two servings of tree nuts a week were excluded, as were people regularly using certain supplements, including fish oil and flaxseed oil. Participants were assessed every two months for factors including weight, tolerance, adherence and medication use.
Researchers used blood samples taken at the start and after two years, and adjusted their comparisons for factors such as age, sex, smoking, study center, cholesterol, body mass index, hypertension and diabetes. In Spanish participants, red blood cell alpha-linolenic acid levels rose substantially in the walnut group and fell in controls, which researchers used as evidence that the assigned diets were followed. The study also found baseline IgG and IgM levels differed by location, with levels lower among US participants than Spanish participants—one reason the country-specific results matter.
Earlier research has linked some antibody measures with cardiovascular outcomes, but those associations do not establish that changing total IgG through diet changes risk. Evidence about antibodies targeting modified LDL has also varied by antibody type. This analysis adds a dietary comparison, but does not resolve whether the observed IgG difference has clinical importance.
“Total IgG concentrations were approximately 6% higher in the walnut group than in controls across both study centers.”
— The study report
What the Biomarker Cannot Establish
The analysis does not show whether higher IgG is beneficial, harmful or neutral in this setting. It did not measure whether participants developed fewer infections, had improved immune function, or experienced fewer cardiovascular events. The clinical meaning of the 6% difference is unknown.
The country-level result also needs care: the analysis found an 11% difference in the US group but no statistically significant effect in Spain. The available report does not establish why results differed by location. The analysis covered blood samples from 474 of the 708 trial participants, and it was conducted after the original trial’s primary research plan, so findings require confirmation in further work.
Research Needed Beyond IgG Levels
The next step is independent research testing whether the total IgG result can be reproduced and whether any change is linked to meaningful health outcomes. Studies designed in advance to examine immune function or cardiovascular events could help distinguish a laboratory-marker shift from a benefit to participants. The source report does not identify a planned follow-up study or a date for further results.
Until then, this finding should be read as a possible dietary effect on one measured antibody level—not proof that walnuts strengthen immunity or prevent heart disease. The study provides no basis for changing treatment or using walnuts in place of medical care.
Key Questions
What did the walnut analysis find?
After two years, participants assigned to eat walnuts had about 6% higher total IgG than controls across both study centers. The US subgroup showed an 11% difference; the study did not find a statistically significant effect in Spain.
Does higher IgG mean stronger immunity?
Not necessarily. IgG is an antibody measure, but this analysis did not test whether the difference improved protection from infection or other aspects of immune function. Its health significance remains unclear.
Did walnuts change the other immune markers?
The analysis found no significant walnut-related effect on total IgM, MDA-LDL, or MDA-LDL-targeting IgM or IgG antibodies. Several measures declined over time in both groups.
How much did participants eat?
The intervention group was assigned to eat 30 to 60 grams of walnuts per day for two years. The trial enrolled cognitively healthy adults aged 63 to 79 in the United States and Spain.
Did the study show walnuts prevent heart disease?
No. The analysis examined blood biomarkers and did not establish that walnut consumption reduced cardiovascular events or prevented atherosclerosis. The researchers said the clinical implications of the IgG result are uncertain.
Source: news-medical.net
