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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 after two years than controls. The result concerns an immune biomarker, not a demonstrated health benefit; researchers found no significant walnut-related changes in several other measured markers, and the clinical meaning of the IgG difference is unknown.
A post hoc analysis of a randomized trial found that adults aged 63 to 79 who were assigned to eat walnuts daily had about 6% higher total serum IgG after two years than participants assigned to avoid walnuts. The finding, reported in JACC Advances, concerns an antibody measure; it does not show that walnuts prevent illness or improve cardiovascular health, and the researchers said the clinical implications remain uncertain.
The analysis drew on the Walnuts and Healthy Aging (WAHA) trial, which enrolled 708 cognitively healthy older adults in the United States and Spain. Participants were randomly assigned to a walnut-based diet or a diet excluding walnuts for two years. The walnut group was asked to eat 30 to 60 grams daily, equivalent to about 15% of daily energy intake.
For this later analysis, researchers measured blood samples from 474 participants: 240 in the walnut group and 234 controls. They assessed total immunoglobulin G (IgG) and immunoglobulin M (IgM), along with antibodies targeting malondialdehyde-modified LDL, or MDA-LDL. The original trial was designed to examine cognitive function and retinal integrity, not these immune markers, so the antibody analysis was post hoc.
The adjusted comparison found total IgG was about 6% higher overall in the walnut group at two years. The difference was not statistically significant in the Spanish participants when examined separately; among U.S. participants, IgG was 11% higher in the walnut group than controls. The study found no significant intervention effect on total IgM, MDA-LDL concentrations, or MDA-LDL-targeting IgM or IgG antibodies. Several measured immune markers declined over time in both groups.
What the IgG Difference Can Tell Us
IgG is one of the main classes of antibodies in blood and is part of the body’s humoral immune response. A higher total concentration is a biomarker finding, not proof that the immune system works better. The trial did not establish that the difference changed participants’ infection risk, cardiovascular events, or other health outcomes.
The question matters because atherosclerosis involves plaque buildup and inflammation in blood vessels, and immune responses to oxidized forms of LDL have been studied in relation to vascular disease. But the meaning of antibody levels depends on what is being measured and the clinical setting. Prior research cited in the report has linked higher total IgG with lower cardiovascular-event risk in a group of people with hypertension, while findings for antibodies specifically targeting MDA-LDL have been mixed. Those associations do not establish that raising IgG through walnuts would reduce risk.
For readers, the result is a reason for further study, not a basis for treating walnuts as an immune therapy. The analysis did not test whether the modest difference led to a measurable benefit, and it offers no evidence that changing IgG levels should be a health goal.
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Inside the WAHA Trial Analysis
The WAHA trial recruited adults in the United States and Spain between May 2012 and May 2014. People who already ate more than two servings of tree nuts per week were excluded, as were people using certain supplements, including soy lecithin, fish oil, or flaxseed oil. Participants attended follow-up visits every two months, where researchers monitored weight, tolerance, diet compliance, and medication use.
Researchers adjusted their comparisons for factors including age, sex, smoking, study center, cholesterol, body mass index, hypertension, and diabetes. Among Spanish participants, red blood cell alpha-linolenic acid levels rose substantially in the walnut group and fell in controls, a finding the researchers used as an indicator of adherence. Baseline IgG and IgM levels differed between the U.S. and Spanish centers, which adds context to the different country-level results.
The study focused on older, cognitively healthy adults who met its eligibility criteria. Its results may not apply to other age groups, people with significant health conditions, or people whose diets and supplement use differ from those of participants.
“The clinical implications remain uncertain.”
— The study authors, as summarized in the News-Medical report
What the Antibody Result Cannot Show
The analysis does not establish why total IgG differed or whether the difference has a meaningful effect on health. It did not show fewer cardiovascular events, infections, or deaths, and the report does not provide evidence that the IgG change itself caused any clinical outcome. The WAHA trial’s primary aims were cognitive and retinal measures, not immune health.
The country-specific results also need care: the overall comparison was statistically significant, but the analysis found no significant effect in Spain and reported a larger difference in the United States. Participants’ baseline antibody levels varied by study center. The available report does not establish what accounts for those differences or whether the pattern would hold in a larger or different population.
As a post hoc analysis of samples from a subset of the original trial, the findings are best treated as hypothesis-generating. More research would be needed to confirm the result, explain its biological relevance, and determine whether it relates to health outcomes.
Evidence Needed Beyond IgG Levels
The next steps are independent studies that test whether the total IgG result can be replicated and examine it alongside clinical outcomes, rather than treating an antibody concentration as a benefit by itself. Researchers would also need to investigate why results differed between the U.S. and Spanish participants and whether diet-related changes in IgG correspond to changes in cardiovascular or immune health.
No further study or follow-up milestone is specified in the report. Until stronger evidence is available, this analysis does not change what can be concluded about walnuts and disease prevention: it identifies a possible association with one blood marker, while the marker’s health significance remains unresolved.
Key Questions
What is IgG?
IgG is a class of antibody found in blood and part of the body’s humoral immune response. Measuring total IgG does not by itself show how well a person is protected from a particular disease.
How many walnuts did participants eat?
People assigned to the walnut diet were asked to eat 30 to 60 grams per day for two years. That amount was estimated to provide about 15% of daily energy intake.
Does the study prove walnuts improve immunity?
No. The analysis found higher total IgG in the walnut group, but it did not show that this change improved immune function or prevented illness. The researchers said the clinical implications remain uncertain.
Did walnuts change the other immune markers measured?
The analysis found no significant walnut-related effect on total IgM, MDA-LDL levels, or MDA-LDL-specific IgM and IgG antibodies. Some markers declined over time in both the walnut and control groups.
Should people eat walnuts to raise IgG?
This study does not establish that raising IgG is beneficial or recommend walnuts as a treatment. People making dietary choices for a health condition should consult a qualified health professional.
Source: news-medical.net
