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ARS Home » Northeast Area » Boston, Massachusetts » Jean Mayer Human Nutrition Research Center On Aging » Research » Publications at this Location » Publication #249028
Title: Chronic and actute effects of walnuts on antioxidant capacity and nutritional status in humans: a randomized, cross-over pilot study

Author
item MCKAY, DIANE - Jean Mayer Human Nutrition Research Center On Aging At Tufts University
item CHEN, CHUNG-YEN (OLIV - Jean Mayer Human Nutrition Research Center On Aging At Tufts University
item YEUM, KYUNG-JIN - Jean Mayer Human Nutrition Research Center On Aging At Tufts University
item MATTHAN, NIRUPA - Jean Mayer Human Nutrition Research Center On Aging At Tufts University
item LICHTENSTEIN, ALICE - Jean Mayer Human Nutrition Research Center On Aging At Tufts University
item BLUMBERG, JEFFREY - Jean Mayer Human Nutrition Research Center On Aging At Tufts University

Submitted to: Nutrition Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2010
Publication Date: 5/12/2010
Citation: Mckay, D.L., Chen, C.E., Yeum, K., Matthan, N.R., Lichtenstein, A.H., Blumberg, J.B. 2010. Chronic and actute effects of walnuts on antioxidant capacity and nutritional status in humans: a randomized, cross-over pilot study. Nutrition Journal. 9(21):1-10.

Interpretive Summary: Compared with other common plant foods, walnuts (Juglans regia) are consistently ranked among the highest in their antioxidant activity. In cell culture experiments and in animal models, the phytochemicals in walnuts have been shown to inhibit LDL oxidation (an indicator of heart disease risk), lower biomarkers of oxidative stress, and raise antioxidant capacity. A limited number of human feeding trials indicate that walnuts improve some measures of antioxidant status, but not others. We conducted a pilot study in 21 generally healthy adults over age 50 to determine if consuming walnuts, as part of their usual diet, changed selected biomarkers of antioxidant activity, oxidative stress, and nutrient status. Compared to baseline levels, red blood cell linoleic acid (an essential fatty acid) and plasma pyridoxal phosphate (vitamin B6) were significantly higher after 6 wk with 42 g/d walnuts (P<0.05 for both). Overall, changes in plasma total thiols, and other antioxidant biomarkers, were not significant with either walnut dose. However, when compared to fasting levels, plasma total thiols were elevated within 1 h of walnut consumption with both doses during the baseline and end visits for each intervention phase (P<0.05 for all). Despite the observed increase in the polyunsaturated fatty acids (linoleic and linolenic acids) associated with walnut consumption, changes in the biomarkers for lipid peroxidation and antioxidant capacity were minimal. There were dose-related changes in lipid peroxidation and antioxidant capacity, but these trends were not significant. In conclusion, walnut consumption did not significantly change the plasma antioxidant capacity of healthy older adults in this pilot study. Future studies investigating the antioxidant effects of walnuts in humans are warranted as studies with a larger sample size, or a controlled feeding intervention, may reveal significant changes.

Technical Abstract: Background Compared with other common plant foods, walnuts (Juglans regia) are consistently ranked among the highest in antioxidant capacity. In vitro, walnut polyphenols inhibit plasma and LDL oxidation, while in animal models they lower biomarkers of oxidative stress and raise antioxidant capacity. A limited number of human feeding trials indicate that walnuts improve some measures of antioxidant status, but not others. Methods A 19 wk, randomized crossover trial was conducted in 21 generally healthy men and postmenopausal women =50 y to study the dose-response effects of walnut intake on biomarkers of antioxidant activity, oxidative stress, and nutrient status. Subjects were randomized to receive either 21 or 42 g raw walnuts/d during each 6 wk intervention phase with a 6 wk washout between phases. Subjects were instructed to consume their usual diet, but refrain from eating any other tree nuts, seeds, peanuts, or ellagitannin-rich foods during the entire study, and other polyphenol-rich foods for 2 d prior to each study visit. Results Compared to baseline levels, red blood cell (RBC) linoleic acid and plasma pyridoxal phosphate (PLP) were significantly higher after 6 wk with 42 g/d walnuts (P<0.05 for both). Overall, changes in plasma total thiols, and other antioxidant biomarkers, were not significant with either walnut dose. However, when compared to fasting levels, plasma total thiols were elevated within 1 h of walnut consumption with both doses during the baseline and end visits for each intervention phase (P<0.05 for all). Despite the observed increase in RBC linoleic and linolenic acids associated with walnut consumption, this substrate for lipid peroxidation only minimally affected malondialdehyde (MDA) and antioxidant capacity. The proportional changes in MDA and Oxygen Radical Absorbance Capacity (ORAC) were consistent with a dose-response effect, although no significant within- or between-group differences were observed for these measures. Conclusions Walnut consumption did not significantly change the plasma antioxidant capacity of healthy, well-nourished older adults in this pilot study. However, these data indicate a trend in a direction that suggests a dose-response relationship. Future studies investigating the antioxidant effects of walnuts in humans are warranted, but should include either a larger sample size or a controlled feeding intervention.