Effects of dairy compared with soy on oxidative and inflammatory stress in overweight and obese subjects

Background: We recently showed that calcitriol increases oxidative and inflammatory stress; moreover, inhibition of calcitriol with high-calcium diets decreased both adipose tissue and systemic oxidative and inflammatory stress in obese mice, whereas dairy exerted a greater effect. However, these findings may be confounded by concomitant changes in adiposity. Objective: The objective of this study was to evaluate the acute effects of a dairy-rich diet on oxidative and inflammatory stress in overweight and obese subjects in the absence of adiposity changes. Design: Twenty subjects (10 obese, 10 overweight) participated in a blinded, randomized, crossover study of dairy-compared with soy-supplemented eucaloric diets. Two 28-d dietary periods were separated by a 28-d washout period. Inflammatory and oxidative stress biomarkers were measured on days 0, 7, and 28 of each dietary period. Results: The dairy-supplemented diet resulted in significant suppression of oxidative stress (plasma malondialdehyde, 22%; 8-isoprostane- F-2 alpha, 12%; P < 0.0005) and lower inflammatory markers (tumor necrosis factor-alpha, 15%, P < 0.002; interleukin-6, 13%, P < 0.01; monocyte chemoattractant protein-1, 10%, P < 0.0006) and increased adiponectin (20%, P < 0.002), whereas the soy exerted no significant effect. These effects were evident by day 7 of treatment and increased in magnitude at the end of the 28-d treatment periods. There were no significant differences in response to treatment between overweight and obese subjects for any variable studied. Conclusion: An increase in dairy food intake produces significant and substantial suppression of the oxidative and inflammatory stress associated with overweight and obesity. This trial was registered at clinicaltrials. gov as NCT00686426. Am J Clin Nutr 2010; 91: 16-22.