Alkylresorcinols of whole grain wheat and rye intake
Rikard Landberg, Matti Marklund, Afaf Kamal-Eldin and Per Åman, Department of Food Science, Swedish University of Agricultural Sciences, Uppsala, Sweden
In nutritional epidemiology, dietary exposure is typically measured by food frequency questionnaires (FFQs) or 24h recalls. These methods may be subjected to considerable systematic and random measurement errors related to the subjects' ability and motivation to report intake accurately. Whole grain intake is suspected to be particularly difficult to report accurately due to different whole grain definitions have been used and because consumers may have difficulties in recognizing whole grain among products as well as the fact that most questionnaires have not been specifically designed to capture whole grain intake.
A biomarker of whole grain intake would have the potential to be a more accurate tool to rank subjects according to their whole grain intake. Wheat and rye (the two most commonly consumed cereals in the Nordic countries) contain alkylresorcinols, a group of phenolic lipids which are found in the bran fraction and not in the white flour or in other commonly consumed foods. Alkylresorcinols fulfill many of the general criteria for being a good biomarker candidate, including:
- Remain stable throughout food processing and storage
- Highly absorbed by humans
- Concentration in biological samples (eg. plasma and erythrocyte membranes) increases in a dose-dependent manner
- Known main routes of elimination
- Possible to quantify from small sample volumes with rather high though-put in biological samples
The Centre in Uppsala is currently leading the development and evaluation of these biomarkers within the HELGA-network. Results, from recent intervention studies have shown that alkylresorcinols and their metabolites can be used as a biomarker for whole grain wheat and rye intake intervention studies where the whole grain is consumed frequent and regularly.
In close collaboration with the other Helga Centers and external collaborators, we are now evaluating the performance of alkylresorcinols and their metabolites as biomarkers in prospective cohort studies. These evaluation studies have included determination of long-term reliability in different cohorts and investigation of dietary and non-dietary determinants of the biomarker concentration in different biological sample matrices. Additionally, a biomarker validation study has been carried out in 90 free-living subjects, where both repeated blood and urine samples (spot urine as well as 24h collections) were collected and detailed information on whole grain intake (g/d) was estimated by weighed food records and a specifically designed FFQ. Data from the evaluation studies are now processed and will be crucial for appropriate implementation of alkylresorcinols and/or their metabolites as biomarkers of whole grain wheat and rye intake in epidemiological endpoint studies. For epidemiological investigations, rapid and cheap methods for the quantification of the biomarker in large sample sets are needed. We have together with external collaborators, started the development of high-throughput methods to fulfill these needs.