A two-year randomized trial involving 474 older adults found that daily consumption of 30–60 grams of walnuts was associated with 6% higher total serum IgG concentrations compared with a control diet, with an 11% difference observed among US participants. Walnut consumption did not significantly affect IgM, MDA-LDL or MDA-LDL-specific antibodies, and whether the modest IgG difference has meaningful cardiovascular benefits remains unknown.