Reliability of fasting plasma alkylresorcinol concentrations measured 4 months apart

Dietary biomarkers-an update on their validity and applicability in epidemiological studies

The aim of this literature review was to identify and provide a summary update on the validity and applicability of the most promising dietary biomarkers reflecting the intake of important foods in the Western diet for application in epidemiological studies. Many dietary biomarker candidates, reflecting intake of common foods and their specific constituents, have been discovered from intervention and observational studies in humans, but few have been validated. The literature search was targeted for biomarker candidates previously reported to reflect intakes of specific food groups or components that are of major importance in health and disease. Their validity was evaluated according to 8 predefined validation criteria and adapted to epidemiological studies; we summarized the findings and listed the most promising food intake biomarkers based on the evaluation. Biomarker candidates for alcohol, cereals, coffee, dairy, fats and oils, fruits, legumes, meat, seafood, sugar, tea, and vegetables were identified. Top candidates for all categories are specific to certain foods, have defined parent compounds, and their concentrations are unaffected by nonfood determinants. The correlations of candidate dietary biomarkers with habitual food intake were moderate to strong and their reproducibility over time ranged from low to high. For many biomarker candidates, critical information regarding dose response, correlation with habitual food intake, and reproducibility over time is yet unknown. The nutritional epidemiology field will benefit from the development of novel methods to combine single biomarkers to generate biomarker panels in combination with self-reported data. The most promising dietary biomarker candidates that reflect commonly consumed foods and food components for application in epidemiological studies were identified, and research required for their full validation was summarized.

Higher Alkylresorcinol Concentrations, a Consequence of Whole-Grain Intake, are Inversely Associated with Gestational Diabetes Mellitus in Iceland

BACKGROUND

A diet rich in whole grains may provide benefits for pregnant women due to whole grains' high nutritional value and dietary fiber content.

OBJECTIVES

To study the associations of whole-grain consumption, as well as the plasma alkylresorcinol concentration, a whole-grain consumption biomarker, in early pregnancy with gestational diabetes mellitus (GDM) diagnoses.

METHODS

Subjects were women from the prospective study Pregnant Women in Iceland II (PREWICE II; n = 853) who attended their ultrasound appointment in gestational weeks 11-14 during the period from October 2017 to March 2018. During that visit, whole-grain consumption was estimated using a diet screening questionnaire, and blood samples were collected for analysis of plasma alkylresorcinols (ARs). Information on GDM diagnoses was later extracted from medical records. Multivariate log-binomial regression was used to evaluate the association of dietary whole-grain and AR concentrations with GDM.

RESULTS

In total, 14.9% of the women adhered to the national food-based dietary guidelines (n = 127), which recommend 2 portions of whole grains daily. GDM was diagnosed in 127 women (14.9%). The frequency of whole-grain consumption was lower in women who were later diagnosed with GDM compared to the women without GDM (median, 5 times/week vs. 6 times/week, respectively; P = 0.02). This difference was reflected in the lower median concentration of total AR in women diagnosed with GDM (163 nmol/L vs. 209 nmol/L, respectively; P < 0.01). The quartile with the highest concentrations of AR had a RR of 0.50 (95% CI: 0.27-0.90) of being diagnosed with GDM, in comparison to the lowest quartile. There was a significant dose response in the GDM risk with higher AR levels.

CONCLUSIONS

We found that a higher consumption of whole grains, reflected both by reported consumption according to the FFQ and AR biomarkers, was associated with a decreased risk of receiving a GDM diagnosis.

Evaluation of alkylresorcinols in adipose tissue biopsies as a long-term biomarker of whole-grain wheat and rye intake in free-living Swedish men and women

OBJECTIVE

Wheat and rye, the most consumed whole grains (WG) in the Nordic countries, contain alkylresorcinols (AR) in their bran. AR concentrations in human adipose tissue might reflect long-term WG rye and wheat intake. We aimed to evaluate AR concentrations in adipose tissue biopsies as a long-term biomarker of WG wheat and rye intake in free-living Swedish men and women.

DESIGN

Cross-sectional study. AR concentrations in adipose tissue biopsies were analysed and compared with long-term WG intake assessed by three FFQ (repeated over a period of 14 years in men, 17 years in women) and with plasma AR concentrations.

SETTING

The Cohort of Swedish Men between 1997 and 2010 and the Swedish Mammography Cohort between 1987 and 2003, Sweden.

SUBJECTS

Men (n 149) and women (n 109).

RESULTS

Long-term WG rye intake estimated with repeated FFQ correlated (r=0·31-0·41, P<0·01) with adipose-tissue AR concentrations, while WG wheat intake correlated only weakly (r=0·17-0·33, P<0·05). Total AR concentration in adipose tissue was 61 % lower in women than in men at similar energy-adjusted WG wheat and rye intakes, but plasma concentrations were similar. AR concentrations in adipose tissue correlated well with plasma concentrations (r=0·49-0·81, P<0·001).

CONCLUSIONS

AR in adipose tissue reflected long-term WG rye but not WG wheat intake, probably due to poor precision in estimating WG wheat intake by FFQ. AR in adipose tissue appears promising as a biomarker of long-term WG rye intake but should be adjusted for sex.

Novel urinary alkylresorcinol metabolites as biomarkers of whole grain intake in free-living Swedish adults

SCOPE

Most studies on the role of whole grain for health rely on self-reported intake data, which are prone to measurement errors. There is a need for dietary biomarkers that can provide an objective measure of intake. Alkylresorcinols (AR) and their main metabolites 3,5-dihydroxybenzoic acid (DHBA) and 3-(3,5-dihydroxyphenyl)-propanoic acid (DHPPA) have been proposed as biomarkers for whole grain (WG) wheat and rye intake.

METHODS AND RESULTS

The medium-term reproducibility and relative validity of four putative urinary AR metabolites (3,5-dihydroxycinnamic acid (DHCA), 5-(3,5-dihydroxyphenyl) pentanoic acid (DHPPTA), 2-(3,5-dihydroxybenzamido)acetic acid (DHBA-glycine) and 3,5-dihydroxycinnamic acid amide (DHCA-amide)) as biomarkers for WG intake were investigated. Three-day weighed food records and 24-h urine samples from two occasions 2-3 months apart were obtained from 69 Swedish adults. WG intake was calculated and urinary AR metabolites were analyzed. The medium-term reproducibility determined for DHCA, DHPPTA, and DHBA-glycine varied from moderate-to-excellent (intra-class correlation coefficient = 0.63-0.85). Moreover, DHCA and DHPPTA excretion correlated well with self-reported total WG intake (r = 0.55, p < 0.001 and r = 0.42, p < 0.001, respectively).

CONCLUSION

DHCA or DHPPTA excretion in 24-h urine might be a suitable medium- to long-term biomarker of WG wheat and rye intake. These findings need to be confirmed in populations with low and infrequent WG intake.

Plasma alkylresorcinols, biomarkers of whole-grain wheat and rye intake, and risk of type 2 diabetes in Scandinavian men and women

BACKGROUND

Studies that use dietary biomarkers to investigate the association between whole-grain intake and the risk of developing type 2 diabetes (T2D) are lacking.

OBJECTIVE

We examined the association between plasma total alkylresorcinols and the alkylresorcinol C17:0-to-C21:0 ratio, biomarkers of whole-grain wheat and rye intake and relative whole-grain rye over whole-grain wheat intake, respectively, and the risk of T2D among Scandinavian men and women.

DESIGN

A nested case-control study was established within the Northern Sweden Health and Disease Study and the Danish Diet, Cancer and Health cohort. Alkylresorcinol concentrations and the ratios of C17:0 to C21:0 were determined in plasma samples from 931 case-control pairs. ORs for T2D were calculated for plasma total alkylresorcinol concentration or C17:0-to-C21:0 ratio in quartiles with the use of conditional logistic regression that was adjusted for potential confounders. Additional analyses with whole-grain wheat and rye intake estimated from food-frequency questionnaires (FFQs) as exposures were also performed.

RESULTS

The plasma total alkylresorcinol concentration was not associated with T2D risk (OR: 1.34; 95% CI: 0.95, 1.88) for the highest compared with the lowest quartiles in multivariable adjusted models. However, the C17:0-to-C21:0 ratio was associated with a lower diabetes risk (OR: 0.54; 95% CI: 0.37, 0.78). Analyses with whole-grain intake estimated from FFQs yielded similar results.

CONCLUSIONS

Total whole-grain wheat and rye intake, reflected by alkylresorcinols in plasma, was not associated with a lower risk of T2D in a population with high whole-grain intake. In contrast, the proportion of whole-grain rye to whole-grain wheat intake, indicated by the plasma C17:0-to-C21:0 ratio, was inversely associated with T2D. This suggests that whole-grain intake dominated by rye may be favorable for T2D prevention.

Validation of Reported Whole-Grain Intake from a Web-Based Dietary Record against Plasma Alkylresorcinol Concentrations in 8- to 11-Year-Olds Participating in a Randomized Controlled Trial

BACKGROUND

Whole-grain (WG) intake is important for human health, but accurate intake estimation is challenging. Use of a biomarker for WG intake provides a possible way to validate dietary assessment methods.

OBJECTIVE

Our aim was to validate WG intake from 2 diets reported by children, using plasma alkylresorcinol (AR) concentrations, and to investigate the 3-mo reproducibility of AR concentrations and reported WG intake.

METHODS

AR concentrations were analyzed in fasting blood plasma samples, and WG intake was estimated in a 7-d web-based diary by 750 participants aged 8-11 y in a 2 school meal × 3 mo crossover trial. Reported WG intake and plasma AR concentrations were compared when children ate their usual bread-based lunch (UBL) and when served a hot lunch meal (HLM). Correlations and cross-classification were used to rank subjects according to intake. The intraclass correlation coefficients (ICCs) between subjects' measurements at baseline and after the UBL were used to assess reproducibility.

RESULTS

Correlations between reported WG wheat + rye intake and plasma AR were 0.40 and 0.37 (P < 0.001) for the UBL and the HLM diets, and 78% and 77% were classified in the same or adjacent quartiles for the UBL and HLM diets, respectively. The ICC over 3 mo was 0.47 (95% CI: 0.38, 0.55) for plasma total ARs and 0.64 (95% CI: 0.58, 0.70) for reported WG intake. Correlations were higher when using the AR C17:0 homolog as a biomarker, reflecting rye intake instead of plasma total ARs [UBL: r = 0.47; HLM: r = 0.43, P < 0.001; ICC = 0.51 (95% CI: 0.43, 0.59)].

CONCLUSIONS

Self-reported WG wheat + rye intake among children showed moderate correlations with plasma AR concentrations. Substantial intraindividual variation was found in WG intake and plasma AR concentrations. The AR homolog C17:0 may be used as a biomarker for WG intake when the WG intake primarily comes from rye as in the present study. This trial was registered at clinicaltrials.gov as NCT01457794.

Comparison of plasma alkylresorcinols (AR) and urinary AR metabolites as biomarkers of compliance in a short-term, whole-grain intervention study

PURPOSE

Alkylresorcinols (AR) are phenolic lipids present in the bran of wheat and rye. Plasma AR and their urinary metabolites may be suitable biomarkers of whole-grain (WG) wheat and rye consumption. The objective of this study was to examine plasma AR and urinary AR metabolites in response to WG wheat consumption.

METHODS

In a randomized crossover study, 19 subjects (10 males, 9 females; BMI 22.0 kg/m(2); age 26 years) incorporated either 3 servings (48 g) or 6 servings (96 g) of WG wheat daily into their regular diet for 1 week. Subjects completed a 2-week washout period, abstaining from all WG consumption, before each intervention. Fasting blood and 24-h urine were collected before and after each intervention. Plasma AR homologues (C19:0, C21:0, C23:0) were quantified by GC-MS after diethyl ether and solid phase extraction and derivatization. Urinary AR metabolites [3,5-dihydroxybenzoic acid and 3-(3,5-dihydroxyphenyl)-propanoic acid] were determined using HPLC with electrochemical detection after enzymatic deconjugation and ethyl acetate extraction.

RESULTS

Urinary total AR metabolites were significantly higher after 6 compared with 3 servings of WG wheat (56 vs. 32 μmol/day, P < 0.001). This dose-response relationship was independent of age, sex, energy intake, and baseline urinary AR metabolite concentration. Plasma total AR tended to be higher after 6 compared with 3 servings of WG wheat (103.0 vs. 86.9 nmol/L), but this difference was not significant (P = 0.42).

CONCLUSION

The results suggest that urinary AR metabolites from 24-h urine collections may be useful as biomarkers of compliance in intervention studies of WG wheat.

Whole grain rye intake, reflected by a biomarker, is associated with favorable blood lipid outcomes in subjects with the metabolic syndrome--a randomized study

Background and Aim

Few studies have explored the possible plasma cholesterol lowering effects of rye consumption. The aim of this secondary analysis in the SYSDIET study was to investigate the association between plasma alkylresorcinols (AR), a biomarker for whole grain wheat and rye intake, and blood lipid concentrations in a population with metabolic syndrome. Furthermore, we analyzed the associations between the AR C17∶0/C21∶0 ratio, a suggested marker of the relative intake of whole grain/bran rye, and blood lipid concentrations.

Methods

Participants were 30–65 years of age, with body mass index (BMI) 27–40 kg/m² and had metabolic syndrome. Individuals were recruited through six centers in the Nordic countries and randomized either to a healthy Nordic diet (ND, n = 93), rich in whole grain rye and wheat, as well as berries, fruits and vegetables, rapeseed oil, three fish meals per week and low-fat dairy products, or a control diet (n = 65) for 18/24 weeks. Associations between total plasma AR concentration and C17∶0/C21∶0 homologue ratio and blood lipids were investigated in pooled (ND + control group) regression analyses at 18/24 weeks adjusted for baseline value for the dependent variable, age, BMI and statin use.

Results

When adjusted for confounders, total plasma AR at 18/24 weeks was not significantly associated with blood lipids but the AR ratio C17∶0/C21∶0 was inversely associated with LDL cholesterol concentrations (B (95% CI): −0.41 (−0.80 to −0.02)), log LDL/HDL cholesterol ratio (−0.20 (−0.37 to −0.03)), log non-HDL cholesterol (−0.20 (−0.37 to −0.03)), log apolipoprotein B (−0.12 (−0.24 to 0.00)) and log triglyceride concentrations (−0.35 (−0.59 to −0.12)).

Discussion

Increased proportion of whole grain rye, reflected by a biomarker, in the diet is associated with favorable blood lipid outcomes, a relationship that should be further investigated.

Trial Registration

ClinicalTrials.gov NCT00992641

Plasma alkylresorcinol concentrations, biomarkers of whole-grain wheat and rye intake, in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort

Whole-grain intake has been reported to be associated with a lower risk of several lifestyle-related diseases such as type 2 diabetes, CVD and some types of cancers. As measurement errors in self-reported whole-grain intake assessments can be substantial, dietary biomarkers are relevant to be used as complementary tools for dietary intake assessment. Alkylresorcinols (AR) are phenolic lipids found almost exclusively in whole-grain wheat and rye products among the commonly consumed foods and are considered as valid biomarkers of the intake of these products. In the present study, we analysed the plasma concentrations of five AR homologues in 2845 participants from ten European countries from a nested case-control study in the European Prospective Investigation into Cancer and Nutrition. High concentrations of plasma total AR were found in participants from Scandinavia and Central Europe and lower concentrations in those from the Mediterranean countries. The geometric mean plasma total AR concentrations were between 35 and 41 nmol/l in samples drawn from fasting participants in the Central European and Scandinavian countries and below 23 nmol/l in those of participants from the Mediterranean countries. The whole-grain source (wheat or rye) could be determined using the ratio of two of the homologues. The main source was wheat in Greece, Italy, the Netherlands and the UK, whereas rye was also consumed in considerable amounts in Germany, Denmark and Sweden. The present study demonstrates a considerable variation in the plasma concentrations of total AR and concentrations of AR homologues across ten European countries, reflecting both quantitative and qualitative differences in the intake of whole-grain wheat and rye.

Self-reported whole-grain intake and plasma alkylresorcinol concentrations in combination in relation to the incidence of colorectal cancer

Self-reported food frequency questionnaires (FFQs) have occasionally been used to investigate the association between whole-grain intake and the incidence of colorectal cancer, but the results from those studies have been inconsistent. We investigated this association using intakes of whole grains and whole-grain products measured via FFQs and plasma alkylresorcinol concentrations, a biomarker of whole-grain wheat and rye intake, both separately and in combination (Howe's score with ranks). We conducted a nested case-control study in a cohort from a research project on Nordic health and whole-grain consumption (HELGA, 1992-1998). Incidence rate ratios and 95% confidence intervals were calculated using conditional logistic regression. Plasma alkylresorcinol concentrations alone and Howe's score with ranks were inversely associated with the incidence of distal colon cancer when the highest quartile was compared with the lowest (for alkylresorcinol concentrations, incidence rate ratio = 0.34, 95% confidence interval: 0.13, 0.92; for Howe's score with ranks, incidence rate ratio = 0.35, 95% confidence interval: 0.15, 0.86). No association was observed between whole-grain intake and any colorectal cancer (colon, proximal, distal or rectum cancer) when using an FFQ as the measure/exposure variable for whole-grain intake. The results suggest that assessing whole-grain intake using a combination of FFQs and biomarkers slightly increases the precision in estimating the risk of colon or rectal cancer by reducing the impact of misclassification, thereby increasing the statistical power of the study.

Plasma alkylresorcinols C17:0/C21:0 ratio, a biomarker of relative whole-grain rye intake, is associated to insulin sensitivity: a randomized study

BACKGROUND/OBJECTIVES

Few studies have used biomarkers of whole-grain intake to study its relation to glucose metabolism. We aimed to investigate the association between plasma alkylresorcinols (AR), a biomarker of whole-grain rye and wheat intake, and glucose metabolism in individuals with metabolic syndrome (MetS).

SUBJECTS/METHODS

Participants were 30-65 years of age, with body mass index 27-40 kg/m(2) and had MetS without diabetes. Individuals were recruited through six centers in the Nordic countries and randomized to a healthy Nordic diet (ND, n=96), rich in whole-grain rye and wheat, or a control diet (n=70), for 18-24 weeks. In addition, associations between total plasma AR concentration and C17:0/C21:0 homolog ratio as an indication of the relative whole-grain rye intake, and glucose metabolism measures from oral glucose tolerance tests were investigated in pooled (ND+control) regression analyses at 18/24 weeks.

RESULTS

ND did not improve glucose metabolism compared with control diet, but the AR C17:0/C21:0 ratio was inversely associated with fasting insulin concentrations (P=0.002) and positively associated with the insulin sensitivity indices Matsuda ISI (P=0.026) and disposition index (P=0.022) in pooled analyses at 18/24 weeks, even after adjustment for confounders. The AR C17:0/C21:0 ratio was not significantly associated with insulin secretion indices. Total plasma AR concentration was not related to fasting plasma glucose or fasting insulin at 18/24 weeks.

CONCLUSIONS

The AR C17:0/C21:0 ratio, an indicator of relative whole-grain rye intake, is associated with increased insulin sensitivity in a population with MetS.

Plasma alkylresorcinols, biomarkers of whole-grain wheat and rye intake, and incidence of colorectal cancer

BACKGROUND

Few studies have investigated the association between whole-grain intake and colorectal cancer. Because whole-grain intake estimation might be prone to measurement errors, more objective measures (eg, biomarkers) could assist in investigating such associations.

METHODS

The association between alkylresorcinols, biomarkers of whole-grain rye and wheat intake, and colorectal cancer incidence were investigated using prediagnostic plasma samples from colorectal cancer case patients and matched control subjects nested within the European Prospective Investigation into Cancer and Nutrition. We included 1372 incident colorectal cancer case patients and 1372 individual matched control subjects and calculated the incidence rate ratios (IRRs) for overall and anatomical subsites of colorectal cancer using conditional logistic regression adjusted for potential confounders. Regional differences (Scandinavia, the Mediterranean, Central Europe) were also explored.

RESULTS

High plasma total alkylresorcinol concentration was associated with lower incidence of distal colon cancer; the adjusted incidence rate ratio of distal colon cancer for the highest vs lowest quartile of plasma total alkylresorcinols was 0.48 (95% confidence interval [CI] = 0.28 to 0.83). An inverse association between plasma total alkylresorcinol concentrations and colon cancer was found for Scandinavian participants (IRR per doubling = 0.83; 95% CI = 0.70 to 0.98). However, plasma total alkylresorcinol concentrations were not associated with overall colorectal cancer, proximal colon cancer, or rectal cancer. Plasma alkylresorcinols concentrations were associated with colon and distal colon cancer only in Central Europe and Scandinavia (ie, areas where alkylresorcinol levels were higher).

CONCLUSIONS

High concentrations of plasma alkylresorcinols were associated with a lower incidence of distal colon cancer but not with overall colorectal cancer, proximal colon cancer, and rectal cancer.

Plasma alkylresorcinol metabolites as biomarkers for whole-grain intake and their association with prostate cancer: a Swedish nested case-control study

BACKGROUND

Observational studies have mostly found no association between self-reported whole-grain intake and prostate cancer. Plasma alkylresorcinol metabolites have been suggested as biomarkers for whole-grain intake in free-living populations.

METHODS

We investigated the major dietary and lifestyle determinants of plasma alkylresorcinol metabolites in a nested case-control study (1,016 cases and 1,817 controls) in the Malmö Diet and Cancer Study. Multivariate adjusted ORs and 95% confidence intervals (95% CI) were estimated to assess the association between plasma alkylresorcinol metabolites and prostate cancer using logistic regression.

RESULTS

Whole-grain intake, waist circumference, educational level, and smoking status were the main determinants of alkylresorcinol metabolites. We observed significant correlations between alkylresorcinol metabolites and whole-grain (r = 0.31) and fiber (r = 0.27) intake. Metabolite concentration was positively associated with prostate cancer risk (Poverall effect = 0.0004) but the association was not linear (P = 0.04). The lowest risk was seen among men with moderate plasma concentrations. The OR for high compared with moderate plasma alkylresorcinol metabolites was 1.41 (95% CI, 1.10-1.80) for prostate cancer.

CONCLUSIONS

Results suggest that plasma alkylresorcinol metabolites are mainly determined by whole-grain intake in this nested case-control study of Swedish men. The increased risk of prostate cancer seen among men with high plasma alkylresorcinol metabolites requires further study, but residual confounding, detection bias, or competing risks of nonprostate cancer-related deaths are plausible explanations that could not be ruled out.

IMPACT

We found no evidence of a protective effect of whole grains on incident prostate cancer. Further validation of alkylresorcinol metabolites as a biomarker for whole-grain intake is needed.

Plasma alkylresorcinols reflect important whole-grain components of a healthy Nordic diet

Biomarkers of dietary intake can be important tools in nutrition research. Our aim was to assess whether plasma alkylresorcinol (AR) and β-carotene concentrations could be used as dietary biomarkers for whole-grain, fruits and vegetables in a healthy Nordic diet (ND). Participants (n = 166), 30-65 y with a body mass index of 27-40 kg/m(2) and two more features of metabolic syndrome (International Diabetes Federation definition, slightly modified), were recruited through six centers in the Nordic countries and randomly assigned to an ND or control diet for 18 or 24 wk, depending on study center. Plasma AR and β-carotene were analyzed and nutrient intake calculated from 4-d food records. Median fiber intake increased in the ND group from 2.5 g/MJ at baseline to 4.1 g/MJ (P < 0.001) at end point (week 18 or 24), and median (IQR) fasting plasma total AR concentration increased from 73 (88) to 106 (108) nmol/L, or 45%, from baseline to end point (P < 0.001). The AR concentration was significantly higher in the ND group (P < 0.001) than in the control group at end point. β-Carotene intake tended to increase in the ND group (P = 0.07), but the plasma β-carotene concentration did not change significantly throughout the study and did not differ between the groups at follow-up. In conclusion, an ND resulted in higher dietary fiber intake and increased plasma total AR concentration compared with the control diet, showing that the total AR concentration might be a valid biomarker for an ND in which whole-grain wheat and rye are important components. No significant difference in plasma β-carotene concentrations was observed between the ND and control groups, suggesting that β-carotene may not be a sensitive enough biomarker of the ND.

Long-term reproducibility of plasma alkylresorcinols as biomarkers of whole-grain wheat and rye intake within Northern Sweden Health and Disease Study Cohort

BACKGROUND/OBJECTIVES

Alkylresorcinols (AR) have been suggested as specific biomarkers of whole-grain (WG) and bran intake from wheat and rye. Before using plasma AR as biomarkers in prospective cohort studies, the long-term reproducibility needs to be determined in order to judge how well a single plasma sample reflects the long-term concentration. The objective was therefore to estimate the reproducibility of plasma AR concentrations over 0.1-3.9 years.

SUBJECTS/METHODS

The concentrations of AR homologues were analysed in plasma samples, drawn>8 h since last meal, 0.1-3.9 years apart (mean ≈ 2 years) in 74 participants in the Swedish prospective Västerbotten Intervention Project cohort. Reproducibility was estimated by calculating the intra class correlation coefficient (ICC).

RESULTS

Fasting plasma AR concentrations were similar between the first and second measurements. The ICC for total AR was 0.54 (95% confidence interval (CI)=0.38-0.69] overall, 0.34 (95% CI=0.13-0.64) for men and 0.73 (95% CI=0.56-0.85) for women, respectively. Somewhat higher ICCs were obtained for shorter AR homologues.

CONCLUSION

In summary, the reproducibility of plasma AR over 0.1-3.9 years was high for women and moderate for men within this population. Together with previous data showing high validity of plasma AR as biomarkers of wheat and rye in different populations, the current finding suggest that this biomarker is stable over a long-time period and is therefore probably useful for assessment of long-term WG intake in populations with a wide intake range and a frequent intake.

Plasma alkylresorcinols, biomarkers of whole-grain intake, are related to lower BMI in older adults

Alkylresorcinols (AR) are phenolic lipids found in the bran fraction of whole-grain wheat, rye, and barley. In intervention studies, plasma AR concentration increased in response to greater intakes of whole grain, wheat, and rye. This study examined the cross-sectional associations between plasma AR and habitual whole-grain intake, BMI, and metabolic risk factors in 407 free-living older adults (166 men and 241 women; aged 60-81y; median BMI: 27 kg/m(2)). Plasma AR were measured by liquid chromatography-tandem MS, and whole-grain intakes were estimated by using an FFQ. After adjustment for fasting TG concentrations, median plasma AR concentrations across quartile categories of AR were 5, 14, 27, and 62 nmol/L, respectively. Spearman correlation coefficients between plasma AR and whole-grain wheat-rich foods and total bran intake were 0.31 and 0.27, respectively (both P < 0.0001). After adjustment for multiple covariates, the geometric means of BMI in the lowest and highest quartile category of plasma AR were 27.6 and 26.7 kg/m(2), respectively (P-trend = 0.04). No associations were observed between plasma AR and glucose and insulin. Our study shows a dose-dependent relationship between whole-grain intake and plasma AR and confirms the previously observed inverse relationship between whole-grain intake and BMI using an independent biomarker of whole-grain wheat intake.

Alkylresorcinol metabolism in Swedish adults is affected by factors other than intake of whole-grain wheat and rye

The urinary alkylresorcinol (AR) metabolites, 3,5-dihydroxybenzoic acid (DHBA) and 3-(3,5-dihydroxyphenyl)-propanoic acid (DHPPA), could potentially serve as biomarkers for intake of whole-grain (WG) wheat and rye. Excretion of AR metabolites is largely dependent on the intake of AR but may also be influenced by other factors. This study aimed to investigate the validity of free and conjugated AR metabolites as biomarkers for WG intake of wheat and rye and to identify potential determinants of AR metabolites in urine. We quantified free aglycones and conjugates of AR metabolites in 24-h urine collections from 52 free-living Swedish adults and calculated correlation coefficients between urinary AR metabolite excretion and self-reported WG intake. We used partial least-squares regression to identify possible determinants of urinary AR metabolites. Approximately 50% of urinary AR metabolites were found as conjugates. Excretions of individually quantified free and conjugated AR metabolites and their sums were correlated to self-reported intake of WG rye and wheat (r = 0.50-0.68; P < 0.001). Excretion of urinary AR metabolites was mainly dependent on intake of 2 major dietary AR homologs, C19:0 and C21:0. Sex, BMI, and vitamin C intake were identified as determinants of the proportion of free and glucuronidated DHPPA in the present study. Urinary AR metabolites may be useful in reflecting short-term to medium-term intake of WG, but urine samples should be deconjugated prior to quantification. Anthropometric and dietary factors affecting the proportion of conjugated AR metabolites in urine may to some extent influence AR elimination and thereby the performance of urinary AR metabolites as biomarkers.

Alkylresorcinol metabolite concentrations in spot urine samples correlated with whole grain and cereal fiber intake but showed low to modest reproducibility over one to three years in U.S. women

Two alkylresorcinol (AR) metabolites, 3, 5-dihydroxybenzoic acid (DHBA) and 3-(3,5-dihydroxyphenyl)-1-propanoic acid (DHPPA), in urine have been suggested as biomarkers of whole grain (WG) and cereal fiber intake but the long-term reproducibility and correlation with habitual intake has not been determined. Therefore, we evaluated the long-term reproducibility of AR metabolites in spot urine samples and investigated their correlation with habitual WG and cereal fiber intake in U.S. women. AR metabolites were analyzed in 104 women participating in the Nurses' Health Study II and WG and fiber intakes were assessed using a FFQ. Long-term reproducibility was assessed by calculating the intra-class correlation coefficients (ICC) using samples taken 1-3 y (mean 1.8 y) apart. The observed Spearman correlation coefficients (r(s)) and r(s) adjusted for within-participant variation in the biomarker were calculated between WG and fiber intake and biomarkers. The long-term reproducibility was poor for DHBA [ICC = 0.17 (95% CI: 0.05, 0.43)] and modest for DHPPA [ICC = 0.31 (95% CI: 0.17, 0.51)]. The correlation between WG intake in 1995 and DHPPA measured 2 y later was 0.37 (P < 0.0001); the adjusted correlation was 0.60 (95% CI: 0.37, 0.76). Cereal fiber and WG intake were similarly correlated to the biomarkers. DHPPA in spot urine samples reflected WG intake despite relatively low intake of food sources of AR. The poor to modest reproducibility may limit the use of single measurements of these biomarkers in cohort studies in the US, where WG intake is relatively low and has changed over time. But DHPPA in repeated samples may be useful for validating WG intake and assessing compliance in WG intervention studies.

Alkylresorcinol metabolites in urine correlate with the intake of whole grains and cereal fibre in free-living Swedish adults

Alkylresorcinols (AR) have been established as short/medium-term biomarkers for whole grain (WG) wheat and rye intake; and AR metabolites, 3,5-dihydroxybenzoic acid and 3-(3,5-dihydroxyphenyl)-propanoic acid, have been suggested as complementary biomarkers to AR. The present study examined the medium-term reproducibility and relative validity of urinary AR metabolites as biomarkers for WG and cereal fibre intake. A total of sixty-six free-living Swedes completed 3 d weighed food records and provided single 24 h urine collections and morning urine spot samples on two occasions, 2-3 months apart. The medium-term reproducibility of urinary AR metabolites was moderate when assessed in 24 h collections and lower in creatinine (CR)-adjusted morning urine. Mean AR metabolite 24 h excretions correlated well with total WG (r(s) 0·31-0·52, P < 0·05) and cereal fibre (r(s) 0·46-0·58, P < 0·001) intake on both occasions. As expected, correlations with WG (r(s) 0·28-0·38, P < 0·05) and cereal fibre (r(s) 0·35-0·42, P < 0·01) were weaker for mean CR-adjusted AR metabolite concentrations in spot samples of morning urine, although the adjusted concentrations correlated well with 24 h urinary excretion (r(s) 0·69-0·73, P < 0·001). Adjustment for intra-individual variations substantially improved the correlations between intake and excretion. These findings suggest that urinary AR metabolites can successfully reflect the medium-term intake of WG and cereal fibre when adjusted for intra-individual variation in this population, where rye was the major contributor to high WG intake. The performance of urinary AR metabolites as medium-term biomarkers appears to be comparable to that of fasting plasma AR concentration in this population.

Present status and perspectives on the use of alkylresorcinols as biomarkers of wholegrain wheat and rye intake

Alkylresorcinols (ARs) were first proposed as potential biomarkers of wholegrain wheat and rye intake a decade ago. Since then there has been a considerable body of research which suggests that ARs do meet most criteria of a biomarker of these foods. Results from human studies on plasma AR and their plasma and urinary metabolites strongly indicate that these compounds are responsive to whole grain wheat and rye intake and are correlated with various measures of AR consumption. This review briefly summarises work on the bioactivities of AR and focuses on aspects related to their use as biomarkers of whole grain wheat and rye intake. Evidence suggests that they thus far broadly fulfil the criteria to act as biomarkers of these cereals. However, there are still gaps in the knowledge on factors relating to the wide interindividual variation, and application to different epidemiological cohorts. Overall, ARs are highly promising biomarkers of whole grain wheat and rye intake and add to our increasing understanding of whole grains and health.

Plasma alkylresorcinols as a biomarker of whole-grain food consumption in a large population: results from the WHOLEheart Intervention Study

BACKGROUND

Small-scale, short-term intervention studies have suggested that plasma alkylresorcinol (AR) concentrations may be biomarkers of whole grain (WG) wheat and rye intakes.

OBJECTIVE

The objective was to determine whether plasma AR concentrations reflect self-reported WG food intake in a 16-wk WG intervention study and to establish which phenotypic characteristics influence plasma AR concentrations.

DESIGN

In a randomized parallel-group dietary intervention study, 316 overweight and obese participants with a WG intake of <30 g/d were recruited and randomly assigned to 1 of 3 groups: control (no dietary change), intervention 1 (60 g WG/d for 16 wk), or intervention 2 (60 g WG/d for 8 wk followed by 120 g WG/d for 8 wk). Fasting blood samples were collected at baseline, 8 wk, and 16 wk for the measurement of plasma lipids and ARs.

RESULTS

Plasma samples from 266 study completers were analyzed. Total plasma AR concentrations increased with the WG intervention and could be used to distinguish between control subjects and those who consumed 60 or 120 g WG, but not between those who consumed 60 and 120 g WG. Plasma AR concentrations were higher in men, were positively associated with plasma triglyceride concentrations, and were negatively associated with nonesterified fatty acids.

CONCLUSIONS

Plasma AR concentrations were correlated with WG intake and could be used to distinguish between low- and high-WG consumers. Sex and plasma lipid concentrations independently influenced plasma AR concentrations, although plasma triglycerides may explain higher concentrations in men. This trial is registered as ISRCT no. 83078872.

Plasma alkylresorcinol concentrations correlate with whole grain wheat and rye intake and show moderate reproducibility over a 2- to 3-month period in free-living Swedish adults

Plasma alkylresorcinols (AR) are useful as dietary biomarkers of wheat and rye whole grain (WG) during interventions but need to be validated in free-living populations. This study estimated the medium-term reproducibility and relative validity of plasma AR as biomarkers of WG and cereal fiber intake. Seventy-two Swedish adults kept 3-d weighed food records on 2 occasions 2-3 mo apart. Of these men and women, 51 provided a fasting blood sample at the end of each occasion. In addition, 18 participants provided 3 fasting and 3 nonfasting samples for 3 consecutive days on the first and second occasions, respectively. Dietary and blood variables did not differ between the 2 occasions. Nonfasting plasma total AR concentration [210 nmol/L (95% CI: 140, 314)] was higher than fasting [99 nmol/L (95% CI: 72, 137)] (P < 0.0001). Mean WG intake was 70 ± 61 g/d (41% from rye) and the intra-class correlation coefficient was 0.44 (95% CI: 0.26, 0.63) for total WG intake and 0.47 (95% CI: 0.27, 0.67) for the fasting plasma total AR concentration, suggesting moderate reproducibility. Fasting plasma total AR moderately correlated with WG rye + wheat (r(s) = 0.53; P < 0.001) and cereal fiber intake (r(s) = 0.32; P < 0.05) when using mean values from both occasions. This suggests that plasma AR concentration in fasting samples can be used as a biomarker of rye + wheat WG intake in free-living populations with a high and consistent WG intake.