Intraindividual Variation in Markers of Intestinal Permeability and Adipose Tissue Inflammation in Healthy...

Intestinal permeability and adipose tissue inflammation are considered mechanistic links in the relationship between diet, obesity, and chronic disease. However, methods to measure both are not well standardized, and the reliability of commonly used measures is not known.

We calculated the intraclass correlation coefficient (ICC) for several common measures of intestinal permeability and adipose tissue inflammation from a randomized clinical trial of cross-over design in which normal-weight (n = 12) or overweight/obese (n = 12) individuals each completed three 8-day dietary intervention periods.

For biomarkers of intestinal permeability, plasma zonulin, and lipopolysaccharide-binding protein, ICCs were "excellent" (i.e., >0.9). The direct measure of intestinal permeability, the lactulose/mannitol test, exhibited "fair" reliability (ICC = 0.53). A wider range of ICCs (0.6-0.9), suggesting "good" to "excellent" reliability, were obtained for measures of adipose tissue expression of genes encoding major mediators of inflammation. Similarly, individual immune cell populations isolated from adipose tissue, expressed as a percentage of all CD45⁺ cells, also had "good" to "excellent" ICCs. However, when these populations were expressed as number of cells per gram of tissue, ICC values were "fair," falling below 0.6.

Due to the repeated measures design, our study offered a unique opportunity to assess reliability of commonly used biomarkers of intestinal permeability and adipose tissue inflammation. Our findings suggest that these measures were generally highly reliable in the short-term.

Along with other factors, particularly validity, the demonstrated reliabilities can help inform the choice of endpoints in studies of intestinal permeability and adipose tissue inflammation.