Compound-Specific Stable Isotope Analysis Improves the Association Between Dairy Fatty Acid Biomarkers and Dairy Intake: A Secondary Analysis.

Increasing evidence suggests that dairy consumption may decrease the risk of chronic diseases. However, this association remains unclear due to methodological limitations. As a part of a secondary analysis, we used compound-specific stable isotope analysis to increase the accuracy of the dairy FA biomarkers (15:0, 17:0), considering that each food item holds a unique stable C isotope (δ13C) signature. Healthy, overweight to obese adults (n = 96) were randomly assigned to one of 3 dietary treatments in a controlled multi-site (Halifax and Toronto, Canada) clinical trial for 12 weeks: (i) calorie-restricted diet; (ii) dairy-rich diet, consisting of 1 serving each of full-fat milk, cheese, and yogurt/day; and (iii) dairy-rich + calorie-restricted (DCR) diet. Content, composition, and δ13C signature of 15:0 and 17:0 were measured in the dairy foods provided, and participants' plasma and red blood cells. We found that the isotopic signatures of plasma 15:0 and 17:0 were more enriched in the high-adherence group of participants in Halifax who consumed dairy (especially the DCR arm), and that these ratios were more similar to the signatures of the dairy food FA sources, thus reflecting dairy consumption. We also observed major differences in the content, composition, and isotopic signature of the target FA between the participants in Halifax and Toronto, which may be related to the different adherence rates, as well as to intrinsic geographic and dietary variations between populations. This study shows a potential use of compound-specific stable isotope analysis to provide more accurate information on dairy FA biomarkers reflecting consumption.