The Dietary Inflammatory Index Is Lower Among Healthy Older Adults Consuming a Walnut-Supplemented Diet. Ancillary Results From the Walnuts and Healthy Aging Randomized Controlled Trial

Background: Walnuts may lower diet-related inflammation by providing anti-inflammatory compounds and displacing proinflammatory nutrients. Objective: The aim of this study was to explore the association between daily walnut consumption or abstention for 2 years and the dietary inflammatory index (DII). Design: The Walnuts and Healthy Aging study is a dual-center (Loma Linda, CA, and Barcelona, Spain), randomized trial, comparing a walnut-rich diet with a control diet over 2 years between May 2012 and May 2016, for age-related outcomes in healthy, free-living older adults aged 63 to 79 years. This ancillary study concerned only the Loma Linda cohort. Participants/setting: A total of 319 older adults (mean age, 69 years; 66% women) from Loma Linda, CA, were randomly assigned to walnut (n = 166) or control (n = 153) diets. Intervention: The walnut group consumed 1 to 2 oz walnuts/day (30-60 g/day, ∼15% of energy), whereas the control group abstained from walnuts and limited other nuts to <2 servings/week. Both groups followed their usual background diet. Main outcome measures: DII scores were calculated from five 24-hour dietary recalls taken at random during the 2-year period. Statistical analysis: Linear mixed models tested DII differences between the walnut and control groups, adjusting for sex, age, body mass index, race, energy intake, smoking status, physical activity, and educational attainment. Results: The mean DII (SE) score was –0.025 (0.14) in the walnut group and 0.615 (0.14) in the control diet group (P < .01). At the nutrient level, n-3 polyunsaturated fatty acids (β = –0.291; 95% CI, –0.450 to –0.132; P < .01), magnesium (β = –0.014; 95% CI, –0.015 to –0.013; P < .01), carbohydrate (β = –0.009; 95% CI, –0.014 to –0.005; P < .01), fiber (β = –0.120; 95% CI, –0.133 to –0.106; P = .05), and protein (β = –0.020; 95% CI, –0.031 to –0.008; P < .01) were associated with a more anti-inflammatory DII score, whereas intake of total and saturated fat was associated with a higher, more proinflammatory, DII score (β = 0.033; 95% CI, 0.020-0.045; P < .01 and β = 0.102; 95% CI, 0.080-0.125; P < .01, respectively). Conclusions: Incorporating walnuts into the habitual diet was associated with more anti-inflammatory DII scores compared with a walnut-free control diet. These findings suggest that adding a single whole food may be a feasible complementary strategy for favorably improving the inflammatory potential of a diet.