How Daily Walnut Consumption Affects Immune Responses in Adults

Glass bottles of milk surrounded by assorted nuts in bowls — Photo: beats1 / Shutterstock

A two-year study of older adults found that eating walnuts every day raised a key immune protein in their blood by about 6%.

Quick Take

A randomized trial of 474 adults ages 63-79 found daily walnuts raised total IgG, a key immune antibody, by about 6% compared to a control diet.
The effect was stronger in U.S. participants, who showed an 11% higher IgG level than those who avoided walnuts.
Participants ate 30 to 60 grams of walnuts a day, about 15% of their daily calories, for two full years.
The study did not find higher protection from disease, just a change in one blood marker, and some other immune markers showed no change at all.
The California Walnut Commission funded the research, which has helped spark renewed public interest.

Trial Tracked Hundreds Of Older Adults For Two Years

Researchers ran the Walnuts and Healthy Aging trial with 708 adults between ages 63 and 79 in Spain and the United States. They randomly split people into two groups. One group added walnuts to their diet. The other group avoided walnuts and cut back on other nuts too. Scientists then tested blood samples from 474 of those participants for immune markers.

People in the walnut group ate between 30 and 60 grams of walnuts daily. That is roughly a handful, making up about 15% of their total daily calories. After two years, researchers measured total IgG, an antibody that helps the body fight infection. The walnut group showed levels about 6% higher than the control group.

U.S. Participants Showed A Bigger Jump Than Spanish Counterparts

The size of the effect was not the same everywhere. Among U.S. participants, IgG levels ran about 11% higher in the walnut group than in the control group. That gap was almost twice the overall study result. Researchers have not yet explained why the U.S. group responded more strongly than the Spanish group.

Possible explanations include differences in starting diets, other health conditions, how closely people stuck to the plan, or simple chance. The study did not test for these factors directly. Until further research digs into participant-level data, the reason behind the geographic split remains an open question for scientists to answer.

Higher Antibody Levels Do Not Equal Proven Health Gains

The walnut group’s results were not uniform across the board. Researchers found no meaningful difference in total IgM, another antibody type, between the two groups. They also found no change in LDL-related antibodies tied to heart disease risk. These gaps limit how broadly the findings can be applied.

Higher IgG is a change in a blood marker, not proof of fewer infections or better vaccine response. The study did not track hospital visits, illness rates, or survival. Researchers say future studies need to test whether this biomarker shift actually leads to stronger real-world immune protection.

Broader Walnut Research Shows A Mixed Track Record

This is not the first walnut study to produce uneven results. A 2022 analysis of 17 trials found walnuts improved blood fat levels but had no clear effect on inflammation markers overall. Another review of nut trials found no significant change in common inflammation signals like CRP and IL-6, despite some favorable results elsewhere.

A separate related analysis from the same research team found the walnut group had a lower Dietary Inflammatory Index score than the control group, with a notable statistical difference. That finding adds some support to the idea that walnuts affect inflammation, even as the immune antibody results stay narrower and more selective.

Industry Funding Adds A Layer Of Scrutiny

The California Walnut Commission funded the Walnuts and Healthy Aging trial. Industry funding does not make the results wrong. Both trial sites used random assignment, a method that strengthens confidence compared to simple observational studies. Readers should know who paid for the research when weighing how outcomes get chosen, framed, and shared with the public.

The study’s reach is also narrow by design. Participants were healthy, independent older adults without major illness. Results may not carry over to people with diabetes, heart disease, weakened immune systems, or those in nursing homes. Researchers say replicating the study in those groups is the needed next step.

For now, the finding stands as a specific, measured change in one blood protein among a defined group of older adults who ate large daily amounts of walnuts for two years. It is not yet a basis for new dietary guidelines, and no public health agency has changed its advice because of it.