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

Dietary biomarkers and food records indicate compliance to study diets in the ADIRA (Anti-inflammatory Diet In Rheumatoid Arthritis) trial

Background

In the ADIRA (Anti-inflammatory Diet In Rheumatoid arthritis) trial, compliance to the study diets has previously been described primarily with a score based on reported intake of trial foods from telephone interviews. The aim of this study was to evaluate compliance using objective dietary biomarkers for whole grain, fruit and vegetables, margarine and oil, seafood and overall fat quality, as well as reported intake from food records of key components of the study diets.

Methods

Fifty patients with rheumatoid arthritis were randomized to begin with the intervention diet (rich in whole grain, fruit and vegetables, margarine/oil and seafood) or the control diet (rich in meat and high-fat dairy) for 10 weeks, followed by a ~ 4 months wash-out period, and then switched diet. Compliance was evaluated using plasma alkylresorcinols (AR) as biomarkers for intake of whole grain wheat and rye, serum carotenoids for fruit and vegetables, plasma linoleic acid (LA, 18:2 n-6) and -α-linolenic acid (18:3, n-3) for margarine and cooking oil, plasma eicosapentaenoic acid (EPA, 20:5 n-3), -docosahexaenoic acid (DHA 22:6, n-3) and -docosapentaenoic acid (22:5 n-3) for seafood, and plasma fatty acid pattern for the overall dietary fat quality. Reported intake of whole grain, fruit, berries and vegetables, seafood, red meat, and fat quality was extracted from 3-d food records.

Results

Plasma AR C21:0 and C23:0, LA, EPA, and DHA were higher while total serum carotenoids were lower after the intervention diet period compared to the control diet period (AR and carotenoids: p = <0.05, fatty acids: p = <0.001). Reported intake of whole grain, fruit, berries and vegetables, and seafood was higher and reported intake of red meat was lower during the intervention diet period compared to the control diet period (p = <0.001). Plasma- and reported fatty acid pattern differed as intended between the diet periods.

Conclusion

This study indicates that the participants in the ADIRA trial were compliant to the study diets regarding intake of whole grain, cooking fat, seafood, and red meat, and the intended overall dietary fat quality. Compliance to instructions on fruit- and vegetable intake remains uncertain.

Clinical trial registration

https://clinicaltrials.gov/ct2/show/NCT02941055?term=NCT02941055&draw=2&rank=1, NCT02941055.

Serum metabolites associated with wholegrain consumption using nontargeted metabolic profiling: a discovery and reproducibility study

PURPOSE

To identify fasting serum metabolites associated with WG intake in a free-living population adjusted for potential confounders.

METHODS

We selected fasting serum samples at baseline from a subset (n = 364) of the prospective population-based Kuopio Ischaemic Heart Disease Risk Factor Study (KIHD) cohort. The samples were analyzed using nontargeted metabolomics with liquid chromatography coupled with mass spectrometry (LC-MS). Association with WG intake was investigated using both random forest followed by linear regression adjusted for age, BMI, smoking, physical activity, energy and alcohol consumption, and partial Spearman correlation adjusted for the same covariates. Features selected by any of these models were shortlisted for annotation. We then checked if we could replicate the findings in an independent subset from the same cohort (n = 200).

RESULTS

Direct associations were observed between WG intake and pipecolic acid betaine, tetradecanedioic acid, four glucuronidated alkylresorcinols (ARs), and an unknown metabolite both in discovery and replication cohorts. The associations remained significant (FDR<0.05) even after adjustment for the confounders in both cohorts. Sinapyl alcohol was positively correlated with WG intake in both cohorts after adjustment for the confounders but not in linear models in the replication cohort. Some microbial metabolites, such as indolepropionic acid, were positively correlated with WG intake in the discovery cohort, but the correlations were not replicated in the replication cohort.

CONCLUSIONS

The identified associations between WG intake and the seven metabolites after adjusting for confounders in both discovery and replication cohorts suggest the potential of these metabolites as robust biomarkers of WG consumption.

Plasma metabolomic profiling of dietary patterns associated with glucose metabolism status: The Maastricht Study

BACKGROUND

Glucose metabolism has been reported to be affected by dietary patterns, while the underlying mechanisms involved remain unclear. This study aimed to investigate the potential mediation role of circulating metabolites in relation to dietary patterns for prediabetes and type 2 diabetes.

METHODS

Data was derived from The Maastricht Study that comprised of 3441 participants (mean age of 60 years) with 28% type 2 diabetes patients by design. Dietary patterns were assessed using a validated food frequency questionnaire (FFQ), and the glucose metabolism status (GMS) was defined according to WHO guidelines. Both cross-sectional and prospective analyses were performed for the circulating metabolome to investigate their associations and mediations with responses to dietary patterns and GMS.

RESULTS

Among 226 eligible metabolite measures obtained from targeted metabolomics, 14 were identified to be associated and mediated with three dietary patterns (i.e. Mediterranean Diet (MED), Dietary Approaches to Stop Hypertension Diet (DASH), and Dutch Healthy Diet (DHD)) and overall GMS. Of these, the mediation effects of 5 metabolite measures were consistent for all three dietary patterns and GMS. Based on a 7-year follow-up, a decreased risk for apolipoprotein A1 (APOA1) and docosahexaenoic acid (DHA) (RR 0.60, 95% CI 0.55, 0.65; RR 0.89, 95% CI 0.83, 0.97, respectively) but an increased risk for ratio of ω-6 to ω-3 fatty acids (RR 1.29, 95% CI 1.05, 1.43) of type 2 diabetes were observed from prediabetes, while APOA1 showed a decreased risk of type 2 diabetes from normal glucose metabolism (NGM; RR 0.82, 95% CI 0.75, 0.89).

CONCLUSIONS

In summary, this study suggests that adherence to a healthy dietary pattern (i.e. MED, DASH, or DHD) could affect the GMS through circulating metabolites, which provides novel insights into understanding the biological mechanisms of diet on glucose metabolism and leads to facilitating prevention strategy for type 2 diabetes.

Alkylresorcinol, a biomarker for whole grain intake, and its association with osteoarthritis: the MOST study

INTRODUCTION

Higher intake of fiber has been associated with lower risk of incident symptomatic osteoarthritis (OA). We examined whether levels of alkylresorcinol (AR), a marker of whole grain intake, were associated with OA in subjects in The Multicenter Osteoarthritis (MOST) Study.

METHOD

Knee x-rays and knee pain were assessed at baseline and through 60-months. Stored baseline fasting plasma samples were analyzed for AR homologues (C17:0, C19:0, C21:0, C23:0, C25:0) and total AR levels (AR sum). Two nested case-control studies, one for incident radiographic OA and one for incident symptomatic OA were performed with participants re-assessed at 15, 30 and 60 months. Multivariable conditional logistic regression with baseline covariates including age, sex, BMI, physical activity, quadriceps strength, race, smoking, depressive symptoms, diabetes and knee injury tested the association of log transformed AR levels with OA outcomes.

RESULTS

Seven hundred seventy-seven subjects were, on average, in their 60's, and most were women. For 60-month cumulative incidence, there was no significant association between quartiles of AR concentration and incident radiographic (e.g., for incident radiographic OA, highest vs lowest quartile of AR sum showed RR = 0.93 (95% CI 0.59, 1.47), and for symptomatic OA RR was 1.22 (95% CI 0.76, 1.94). In secondary analyses examining 30-month incidence, high AR levels were associated with a reduced risk of X-ray OA (RR = 0.31 (95% CI 0.15, 0.64).

CONCLUSION

In primary analyses, AR levels were not associated with risk of OA, but secondary analyses left open the possibility that high AR levels may protect against OA.

Reproducibility of the Blood and Urine Exposome: A Systematic Literature Review and Meta-Analysis

Endogenous and exogenous metabolite concentrations may be susceptible to variation over time. This variability can lead to misclassification of exposure levels and in turn to biased results. To assess the reproducibility of metabolites, the intraclass correlation coefficient (ICC) is computed. A literature search in three databases from 2000 to May 2021 was conducted to identify studies reporting ICCs for blood and urine metabolites. This review includes 192 studies, of which 31 studies are included in the meta-analyses. The ICCs of 359 single metabolites are reported, and the ICCs of 10 metabolites were meta-analyzed. The reproducibility of the single metabolites ranges from poor to excellent and is highly compound-dependent. The reproducibility of bisphenol A (BPA), mono-ethyl phthalate (MEP), mono-n-butyl phthalate (MnBP), mono-2-ethylhexyl phthalate (MEHP), mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono-benzyl phthalate (MBzP), mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), methylparaben, and propylparaben is poor to moderate (ICC median: 0.32; range: 0.15-0.49), and for 25-hydroxyvitamin D [25(OH)D], it is excellent (ICC: 0.95; 95% CI, 0.90-0.99). Pharmacokinetics, mainly the half-life of elimination and exposure patterns, can explain reproducibility. This review describes the reproducibility of the blood and urine exposome, provides a vast dataset of ICC estimates, and hence constitutes a valuable resource for future reproducibility and clinical epidemiologic studies.

Variation on a theme: the structures and biosynthesis of specialized fatty acid natural products in plants

Plants are able to construct lineage-specific natural products from a wide array of their core metabolic pathways. Considerable progress has been made toward documenting and understanding, for example, phenylpropanoid natural products derived from phosphoenolpyruvate via the shikimate pathway, terpenoid compounds built using isopentyl pyrophosphate, and alkaloids generated by the extensive modification of amino acids. By comparison, natural products derived from fatty acids have received little attention, except for unusual fatty acids in seed oils and jasmonate-like oxylipins. However, scattered but numerous reports show that plants are able to generate many structurally diverse compounds from fatty acids, including some with highly elaborate and unique structural features that have novel bioproduct functionalities. Furthermore, although recent work has shed light on multiple new fatty acid natural product biosynthesis pathways and products in diverse plant species, these discoveries have not been reviewed. The aims of this work, therefore, are to (i) review and systematize our current knowledge of the structures and biosynthesis of fatty acid-derived natural products that are not seed oils or jasmonate-type oxylipins, specifically, polyacetylenic, very-long-chain, and aromatic fatty acid-derived natural products, and (ii) suggest priorities for future investigative steps that will bring our knowledge of fatty acid-derived natural products closer to the levels of knowledge that we have attained for other phytochemical classes.

Pregnancy outcomes with differences in grain consumption: a randomized controlled trial

OBJECTIVES

Contemporary obstetrics has begun to appreciate the importance of diet in pregnancy, but guidelines are not based on robust data. The hypothesis that a whole grains diet improves pregnancy outcomes is tested in this study. We compared maternal and neonatal outcomes for a pregnancy diet containing 75% of total carbohydrates as refined grains with outcomes for a diet with 75% of total carbohydrates as whole grains.

METHODS

This was a randomized interventional study in a clinic population over the last 4-7 months of normal pregnancy with extensive compliance measures. Besides obstetrical and neonatal outcomes, anthropometric measurements were done. In addition to food frequency questionnaires (FFQs), total plasma alkyl resorcinols, a unique quantitative measure of whole grains, were used as a measure of whole grain consumption.

RESULTS

The data show effective compliance and no difference in outcomes between the diets with regard to maternal weight gain, birth weights, subcutaneous fat and glucose tolerance.

CONCLUSIONS

Ensuring compliance to a proper pregnancy diet resulted in satisfactory weight gain and normal outcomes even when the proportion of whole grains consumed is only 25% of total carbohydrates.

A randomized controlled trial of the effects of whole grains versus refined grains diets on the microbiome in pregnancy

Dietary whole grain consumption has been postulated to have metabolic benefits. The purpose of this study was to compare a pregnancy diet containing 75% of total carbohydrates as refined grains with a diet of 75% of total carbohydrates as whole grains for pregnancy outcomes and effects on the microbiome. Gestational weight gain, glucose tolerance and newborn outcomes were measured on 248 enrolled compliant women from whom a subset of 103 women consented to give 108 vaginal and 109 anal swabs. The data presented here are limited to the patients from whom the vaginal and anal swabs were obtained in order to study the microbiome. A microbiome—16SrRNA survey—was characterized in these samples. Samples and measurements were obtained at the first obstetrical visit, before beginning a prescribed diet (T1—baseline) and after 17–32 weeks on the prescribed diet (T3). Food frequency questionnaires and total plasma alkylresorcinols were used as a measure of whole grain consumption. There were no dietary differences in maternal weight gain, birth weight, or glucose tolerance test. Mothers consuming the whole grains diet showed a trend of gestational decrease in vaginal bacterial alpha diversity, with increasing Lactobacillus-dominance. No significant difference was observed for the anal microbiome. The results suggest that diet modulations of the vaginal microbiome during gestation may have important implications for maternal and neonatal health and in the intergenerational transfer of maternal microbiome.

Trial registration: ClinicalTrials.gov Identifier: NCT03232762.

Effects of substitution dietary guidelines targeted at prevention of IHD on dietary intake and risk factors in middle-aged Danish adults: the Diet and Prevention of Ischemic Heart Disease: a Translational Approach (DIPI) randomised controlled trial

The objective was to investigate the effects of substitution (SUB) dietary guidelines (DG) targeted at the prevention of IHD on dietary intake and IHD risk factors in Danish adults with minimum one self-assessed IHD risk factor. A 6-month single-blinded parallel randomised controlled trial with a follow-up at month 12 included 219 subjects (median age 51 years, 59 % female, 73 % overweight or obese) randomised into an SUB DG, an official (OFF) DG or a control group following their habitual diet (HAB). Participants in the DG intervention groups received bi-weekly reminders of their DG and recipes for dishes and the HAB group received a greeting. Dietary intake and fasting blood, anthropometric and blood pressure measurements were obtained at baseline, month 6 and month 12. Linear regression analyses were applied. At month 6, when compared with the HAB, the SUB had a greater impact on the extent of dietary changes with increased intake of whole grains, dietary fibre and low fibre vegetables compared with the OFF DG, and both DG groups had similar decreased percentage of energy (E%) intake from SFA. The extent of dietary changes was similar at month 12. No overall significant changes from baseline were found in blood pressure, anthropometrics and IHD risk markers. In conclusion, both SUB and OFF DG resulted in cardioprotective dietary changes. However, neither the SUB nor the OFF DG resulted in any overall effects on the selected intermediate risk factors for IHD.

Development and validation of the FiberScreen: A short questionnaire to screen fibre intake in adults

Background

Health effects of dietary fibres are the topic of many studies. Eligibility criteria often include a certain fibre intake, which requires dietary screening during recruitment. However, dietary assessment methods are extensive and burdensome for both the researcher and participant. Therefore, we developed and validated a short questionnaire (FiberScreen) to screen fibre intake.

Methods

The initial five‐item questionnaire assessed fruit, vegetable, whole grain, pasta/rice/potato and legume intake. The optimised FiberScreen included 18 items, which further specified intake of the above‐mentioned categories, and included nuts and seeds. The FiberScreen was completed during two fibre promoting interventions. In Study A, participants without constipation completed the five‐item FiberScreen and a food frequency questionnaire (FFQ) during screening (n = 131), and the 18‐item FiberScreen and a FFQ at 3‐month follow‐up (n = 87). In Study B, 29 constipated participants completed the 18‐item FiberScreen at screening and a FFQ during the first study visit.

Results

The fibre estimate from the five‐item FiberScreen and the FFQ was moderately correlated (r = 0.356, p < 0.001). Importantly, the 18‐item FiberScreen and FFQ, when data of both studies were combined, had a strong correlation (r = 0.563, p < 0.001). The 18‐item FiberScreen had a lower fibre estimate compared to the FFQ (Δ = 1.2 ± 5.9 g, p = 0.030) but the difference was relatively small. Bland–Altman plots showed a good agreement between the questionnaires. Completion time of the 18‐item FiberScreen was 4.2 ± 2 min.

Conclusions

The 18‐item FiberScreen is a suitable short screening questionnaire for ranking the fibre intake of adults. The 18‐item FiberScreen can help to reduce screening burden for both the participant and researcher.

 

Dietary screening during recruitment is more elaborate than is often needed, and burdensome for both the researcher and participant.

An 18‐item FiberScreen questionnaire to screen fibre intake was developed and validated in Dutch adults with and without gastrointestinal complaints.

The 18‐item FiberScreen had a good agreement with a food frequency questionnaire.

Completion time of the 18‐item FiberScreen was around 4 min, compared to 45–60 min for the food frequency questionnaire.

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.

Presence of Fermentable Oligo-, Di-, Monosaccharides, and Polyols (FODMAPs) in commonly eaten foods: extension of a database to indicate dietary FODMAP content and calculation of intake in the general population from food diary data

Background

FODMAPs (Fermentable Oligo-, Di-, Monosaccharides And Polyols) are known for their health benefits but their fermentation may trigger gastrointestinal symptoms and a low-FODMAP diet is a commonly used intervention for functional gastrointestinal disorders. The use of direct measures of FODMAP is labor intensive and expensive and to facilitate the assessment of FODMAP intake in research and clinical work, a nutritional content database with good quality estimates on FODMAP values is needed. Further, the average intake of FODMAP in a general population would be a useful reference and knowledge of the most commonly eaten foods containing FODMAPs would facilitate clinical work utilizing FODMAP diet interventions.

Methods

A nutritional content database was extended with published FODMAP content data. The database was used to calculate FODMAP intake from four-day food diaries from 117 individuals from the general population in Sweden and the most common food items containing FODMAPs were identified.

Results

FODMAP content for 1060 food items was added to the database resulting in 1805 listed FODMAP values. Mean intake of total FODMAP in the diaries was 19 g (fructose: 15.2 g; fructan: 3.5 g; lactose: 14.1 g; galacto-oligosaccharides (GOS) 0.43 g and polyols 1.3 g per day). Overall the most common eaten food items containing FODMAPs were rye and wheat based foods.

Conclusion

Intake of FODMAPs as calculated using the extended database were in line with previous studies supporting its use of the database in both research and clinical interventions. The lists of the most commonly eaten FODMAP food items are provided and may be used to facilitate FODMAP diet interventions.

Increasing dietary fibre intake in healthy adults using personalised dietary advice compared with general advice: a single-blind randomised controlled trial

Objective:

A high-fibre diet is associated with a lower risk for diseases. However, few adults meet the dietary fibre recommendation. Therefore, the effects and acceptance of an algorithm-generated personalised dietary advice (PDA) compared with general advice (GA) on fibre intake were investigated.

Design:

A 6-week, single-blind randomised controlled trial with a 3-month follow-up.

Setting:

PDA was based on habitual intake and provided fibre-rich alternatives using a website; GA contained brochures. Dietary intake was assessed at baseline, week 1, week 6 and 3-month follow-up. Both groups evaluated their advice at week 6. All participants had access to PDA from week 7 until 3-month follow-up.

Participants:

Two groups of healthy adults: PDA (n 34) and GA (n 47). For 3-month follow-up analysis, participants were re-divided into visitors (n 52) and non-visitors (n 26) of the PDA.

Results:

At week 6, energy intake remained stable in both groups, but fibre intake per 1000 kcal increased non-significantly in both groups (PDA = Δ0·5 ± 2·8; GA = Δ0·8 ± 3·1, P = 0·128). Importantly, a significantly higher percentage of PDA participants adhered to the recommendation compared with week 1 (PDA = 21 % increase; GA = 4 % increase, P ≤ 0·001). PDA participants evaluated the advice significantly better compared with GA participants. At 3-month follow-up, fibre intake increased compared with baseline (visitors = Δ2·2 ± 2·6, P < 0·001; non-visitors = Δ1·5 ± 1·9, P = 0·001), but was insignificantly different between groups. Visitors had a decrease and non-visitors had an increase in energy intake (visitors =Δ − 132 ± 525; non-visitors = Δ109 ± 507, P = 0·055).

Conclusions:

The algorithm-generated PDA was well accepted and stimulated adherence to the recommendations more than GA, indicating to be a suitable and cost-efficient method for improving dietary fibre intake in healthy adults.

Simplified method for the measurement of plasma alkylresorcinols: Biomarkers of whole-grain intake

RATIONALE

Consumption of whole grains is negatively associated with cardiovascular disease (CVD) risk but quantification of whole-grain intake is challenging. Alkylresorcinols (ARs) are biomarkers of whole-grain intake. Current methods for AR quantification involve a time-consuming multi-step separation process that hampers applicability in large-scale studies.

METHODS

We developed a streamlined method to quantify ARs in human plasma based on protein precipitation and direct injection into an ultra-high-performance liquid chromatograph coupled to a quadrupole time-of-flight mass spectrometer operating in atmospheric pressure chemical ionization negative ion mode.

RESULTS

Separation of five major ARs was achieved, with linearity in the 5 to 550 nmol/L range and a lower limit of detection (LOD) of 0.5 nmol/L and quantification (LOQ) of 5 nmol/L. The within-run and between-run precision and accuracy were below 15%, and recoveries above 90%. Once validated, the method was applied to measure concentrations of plasma ARs in subjects who participated in a randomized, crossover trial evaluating the effect of carbohydrate type on CVD risk factors. The unrefined carbohydrate diet with the highest fiber content resulted in the highest plasma AR concentration (93 ± 78 nmol/L), and was significantly different (p <0.01) from lower fiber diets (18 ± 26 nmol/L and 19 ± 26 nmol/L, simple and unrefined carbohydrate, respectively).

CONCLUSIONS

This method offers a simplified approach to measure concentrations of plasma ARs as an objective biomarker of whole-grain intake that can be applied to large-scale cohort studies.

Bioavailability and Bioactivity of Alkylresorcinols from Different Cereal Products

Cereal products are the most important dietary source for energy intake and several bioactive compounds with high concentrations in the bran and the germ. Different cereal products provide a rich source of bioactive phytochemicals, namely, phenolic acids, carotenoids, tocopherols, alkylresorcinols, benzoxazines, phytosterols, and lignans. The bioactive substance alkylresorcinols (ARs) present in the whole cereal can inhibit enzyme activity, prevent bacterial or fungal infection, reduce cholesterol absorption, prevent cancer, and resist oxidation. In this paper, we discussed the biological activity of ARs in whole cereal products. Understanding the effects of processing on cereal phytochemicals will help us to develop improved processes for processing cereal foods with higher retention rates of bioactive compounds.

Biomarkers of Whole-Grain and Cereal-Fiber Intake in Human Studies: A Systematic Review of the Available Evidence and Perspectives

High whole-grain consumption is related to better health outcomes. The specific physiological effect of these compounds is still unrevealed, partly because the accurate estimation of the intake of whole grains from dietary assessments is difficult and prone to bias, due to the complexity of the estimation of the intake by the consumer. A biomarker of whole-grain intake and type of whole-grain intake would be useful for quantifying the exposure to whole-grain intake. In this review, we aim to review the evidence on the potential biomarkers for whole-grain intake in the literature. We conducted a systematic search in Medline, Embase, Web of Science, and the Cochrane database. In total, 39 papers met the inclusion criteria following the PRISMA guidelines and were included. The relative validity, responsiveness, and reproducibility of these markers were assessed for short-, medium-, and long-term exposure as important criteria for the potential use of these biomarkers from a clinical and research perspective. We found three major groups of biomarkers: (1) alkylresorcinol, as well as its homologs and metabolites, assessed in plasma, adipose tissue biopsies, erythrocyte membranes, and urine; (2) avenacosides, assessed in urine samples; and (3) benzoxazinoid-derived phenylacetamide sulfates, assessed in blood and urine samples. The reviewed biomarkers may be used for improved assessment of associations between whole-grain intake and health outcomes.

Biomarkers of cereal food intake

Background/objectives

Cereal foods are major contributors to the daily energy, protein, and dietary fiber intake all over the world. The role of cereals in human health is dependent on whether they are consumed as refined or whole grain and on cereal species. To unravel the underlying mechanisms of health effects attributed to specific cereal foods and to provide more precise dietary advice, there is a need for improved dietary assessment of whole-grain intake. Dietary biomarkers of specific cereals, different fractions or cereal-containing foods could offer such a possibility. The aim of this review was to summarize the current status on biomarkers of different cereals, fractions, and specific cereal foods.

Subjects and methods

A literature review was conducted and putative biomarkers of different cereals and pseudo-cereals (wheat, oats, rye, barley, rice, and quinoa) as well as for different grain fractions (whole grain, refined grain, bran) and foods were summarized and discussed.

Results

Several putative biomarkers have been suggested for different cereals, due to their unique presence in these grains. Among the biomarkers, odd-numbered alkylresorcinols are the most well-studied and -evaluated biomarkers and reflect whole-grain wheat and rye intake. Even-numbered alkylresorcinols have been suggested to reflect quinoa intake. Recent studies have also highlighted the potential of avenanthramides and avenacosides as specific biomarkers of oat intake, and a set of biomarkers have been suggested to reflect rice bran intake. However, there are yet no specific biomarkers of refined grains. Most biomarker candidates remain to be evaluated in controlled interventions and free-living populations before applied as biomarkers of intake in food and health studies.

Conclusion

Several putative biomarkers of different cereals have been suggested and should be validated in human studies using recently developed food intake biomarker validation criteria.

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.

Biomarkers of food intake and nutrient status are associated with glucose tolerance status and development of type 2 diabetes in older Swedish women

Background: Diet is frequently associated with both the development and prevention of type 2 diabetes (T2D), but there is a lack of objective tools for assessing the relation between diet and T2D. Biomarkers of dietary intake are unconfounded by recall and reporting bias, and using multiple dietary biomarkers could help strengthen the link between a healthy diet and the prevention of T2D.Objective: The objective of this study was to explore how diet is related to glucose tolerance status (GTS) and to future development of T2D irrespective of common T2D and cardiovascular disease risk factors by using multiple dietary biomarkers.Design: Dietary biomarkers were measured in plasma from 64-y-old Swedish women with different GTS [normal glucose tolerance (NGT; n = 190), impaired glucose tolerance (IGT; n = 209), and diabetes (n = 230)]. The same subjects were followed up after 5 y to determine changes in glucose tolerance (n = 167 for NGT, n = 174 for IGT, and n = 159 for diabetes). ANCOVA and logistic regression were used to explore baseline data for associations between dietary biomarkers, GTS, and new T2D cases at follow-up (n = 69).Results: Of the 10 dietary biomarkers analyzed, β-alanine (beef) (P-raw < 0.001), alkylresorcinols C17 and C19 (whole-grain wheat and rye) (P-raw = 0.003 and 0.011), eicosapentaenoic acid (fish) (P-raw = 0.041), 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) (fish) (P-raw = 0.002), linoleic acid (P-raw < 0.001), oleic acid (P-raw = 0.003), and α-tocopherol (margarine and vegetable oil) (P-raw < 0.001) were associated with GTS, and CMPF (fish) (OR: 0.72; 95% CI: 0.56, 0.93; P-raw = 0.013) and α-tocopherol (OR: 0.71; 95% CI: 0.51, 0.98; P-raw = 0.041) were inversely associated with future T2D development.Conclusions: Several circulating dietary biomarkers were strongly associated with GTS after correction for known T2D risk factors, underlining the role of diet in the development and prevention of T2D. To our knowledge, this study is the first to use multiple dietary biomarkers to investigate the link between diet and disease risk.

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.

Serum alkylresorcinols as biomarkers of dietary gluten exposure in coeliac disease

BACKGROUND

Therapy for coeliac disease (CD) mainly relies on following a gluten-free diet (GFD); however, a serum marker for gluten intake has yet to be established.

AIM

To evaluate the utility of alkylresorcinol concentrations for detecting gluten intake in studies of human and mouse.

METHODS

Alkylresorcinol concentrations were compared among treated patients with coeliac disease (n = 34), untreated coeliac disease patients (n = 36) and controls (n = 33). Furthermore, seven additional coeliac disease patients whose serum samples were available at diagnosis and after GFD were evaluated. In mice studies, alkylresorcinol concentrations were compared in the serum of five mice fed a regular chow and 10 mice fed lifelong with a gluten-free chow. In addition, the effect of adding gluten on changes of alkylresorcinol concentrations was also evaluated.

RESULTS

Total alkylresorcinol concentrations were significantly lower in treated with coeliac disease [median (IQR), 3 (2-8) nmol/L], compared to untreated patients [median (IQR), 32 (11-74) nmol/L; P < 0.0001] or healthy controls [median (IQR), 54 (23-112) nmol/L; P < 0.0001]. Moreover, alkylresorcinol concentrations in coeliac disease patients significantly decreased after introduction of a GFD (median, 34 nmol/L at diagnosis vs. 5 nmol/L after GFD, P = 0.02). In the mice, median (IQR) total alkylresorcinol concentrations in serum samples of mice fed lifelong with a gluten-free chow was 1.8 (1.6-2.3) nmol/L, which was further significantly increased to 16 (11-22) nmol/L after 8 days of feeding with the gluten-free chow that had gluten added to it. (P = 0.008).

CONCLUSION

Serum alkylresorcinol concentrations could be a useful marker for dietary gluten in coeliac disease.

Plasma Alkylresorcinols Reflect Gluten Intake and Distinguish between Gluten-Rich and Gluten-Poor Diets in a Population at Risk of Metabolic Syndrome

BACKGROUND

Many patients with celiac disease experience difficulties in adherence to a gluten-free diet. Methods for testing compliance to a gluten-free diet are costly and cumbersome. Thus, a simple biomarker of gluten intake is needed in a clinical setting and will be useful for epidemiologic studies investigating wider effects of gluten intake.

OBJECTIVE

The aim was to evaluate plasma total alkylresorcinol concentrations as a measure of gluten intake.

METHODS

In this randomized, controlled, crossover intervention study in 52 Danish adults with features of the metabolic syndrome, we compared 8 wk of a gluten-rich and gluten-poor diet separated by a washout period of ≥6 wk. We measured fasting plasma concentrations of alkylresorcinols to determine if they reflected differences in gluten intake as a secondary outcome of the original study. In addition, we investigated in 118 Danish adults the cross-sectional association between self-reported gluten intake and plasma alkylresorcinols in the same and a similar study at baseline. We used mixed-model ANCOVA for examining treatment effects, a classification tree to determine compliance to the gluten-poor diet, and linear regression models for examining baseline correlation between plasma alkylresorcinol concentrations and gluten intake.

RESULTS

Plasma total alkylresorcinols decreased more during the gluten-poor period (geometric mean: -124.8 nmol/L; 95% CI: -156.5, -93.0 nmol/L) than in the gluten-rich period (geometric mean: -31.8 nmol/L; 95% CI: -63.1, -0.4 nmol/L) (P < 0.001). On the basis of the plasma alkylresorcinol profile, we built a classification tree to objectively determine compliance and found an overall participant misclassification error of 3.9%. In the cross-sectional study we found a 5.6% (95% CI: 2.4%, 8.9%) increase in plasma total alkylresorcinols per 1-g increase in reported gluten intake (P < 0.001).

CONCLUSION

We propose the use of plasma alkylresorcinols to monitor compliance to a gluten-free diet as well as to help investigations into the possible effects of gluten in the wider population. This trial was registered at www.clinicaltrials.gov as NCT017119913 and NCT01731366.

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.

Nutritional Cognitive Neuroscience: Innovations for Healthy Brain Aging

Nutritional cognitive neuroscience is an emerging interdisciplinary field of research that seeks to understand nutrition's impact on cognition and brain health across the life span. Research in this burgeoning field demonstrates that many aspects of nutrition—from entire diets to specific nutrients—affect brain structure and function, and therefore have profound implications for understanding the nature of healthy brain aging. The aim of this Focused Review is to examine recent advances in nutritional cognitive neuroscience, with an emphasis on methods that enable discovery of nutrient biomarkers that predict healthy brain aging. We propose an integrative framework that calls for the synthesis of research in nutritional epidemiology and cognitive neuroscience, incorporating: (i) methods for the precise characterization of nutritional health based on the analysis of nutrient biomarker patterns (NBPs), along with (ii) modern indices of brain health derived from high-resolution magnetic resonance imaging (MRI). By integrating cutting-edge techniques from nutritional epidemiology and cognitive neuroscience, nutritional cognitive neuroscience will continue to advance our understanding of the beneficial effects of nutrition on the aging brain and establish effective nutritional interventions to promote healthy brain aging.

The use of mass spectrometry for analysing metabolite biomarkers in epidemiology: methodological and statistical considerations for application to large numbers of biological samples

Data quality is critical for epidemiology, and as scientific understanding expands, the range of data available for epidemiological studies and the types of tools used for measurement have also expanded. It is essential for the epidemiologist to have a grasp of the issues involved with different measurement tools. One tool that is increasingly being used for measuring biomarkers in epidemiological cohorts is mass spectrometry (MS), because of the high specificity and sensitivity of MS-based methods and the expanding range of biomarkers that can be measured. Further, the ability of MS to quantify many biomarkers simultaneously is advantageously compared to single biomarker methods. However, as with all methods used to measure biomarkers, there are a number of pitfalls to consider which may have an impact on results when used in epidemiology. In this review we discuss the use of MS for biomarker analyses, focusing on metabolites and their application and potential issues related to large-scale epidemiology studies, the use of MS "omics" approaches for biomarker discovery and how MS-based results can be used for increasing biological knowledge gained from epidemiological studies. Better understanding of the possibilities and possible problems related to MS-based measurements will help the epidemiologist in their discussions with analytical chemists and lead to the use of the most appropriate statistical tools for these data.

Biomarkers of Dietary Intake Are Correlated with Corresponding Measures from Repeated Dietary Recalls and Food-Frequency Questionnaires in the Adventist Health Study-2

BACKGROUND

Accurate assessment of diet in study populations is still a challenge. Some statistical strategies that use biomarkers of dietary intake attempt to compensate for the biasing effects of reporting errors.

OBJECTIVE

The objective was to correlate biomarkers of dietary intake with 2 direct measures of dietary intake.

METHODS

Subjects provided repeated 24-h dietary recalls and 2 food-frequency questionnaires (FFQs) separated by ∼3 y. Correlations between biomarkers and reported dietary intakes as measured by the recalls and FFQs were de-attenuated for within-person variability. The Adventist Health Study-2 (AHS-2) has a large database of biomarkers of dietary intake (blood, urine, adipose tissue) from a calibration study (909 analytic subjects) representing the cohort. Participants were black and non-black Adventists in the United States and Canada.

RESULTS

Dietary items with higher-valued de-attenuated correlations (≥0.50) between biomarkers and recalls included some fatty acids (FAs), the non-fish meats, fruit (non-black subjects), some carotenoids, vitamin B-12 (non-black subjects), and vitamin E. Moderately valued correlations (0.30-0.49) were found for very long chain ω-3 (n-3) FAs, some carotenoids, folate, isoflavones, cruciferous vegetables, fruit (black subjects), and calcium. The highest correlation values in non-black and black subjects were 0.69 (urinary 1-methyl-histidine and meat consumption) and 0.72 (adipose and dietary 18:2 ω-6), respectively. Correlations comparing biomarkers with recalls were generally similar for black and non-black subjects, but correlations between biomarkers and the FFQ were slightly lower than corresponding recall correlations. Correlations between biomarkers and a single FFQ estimate (the usual cohort situation) were generally much lower.

CONCLUSIONS

Many biomarkers that have relatively high-valued correlations with dietary intake were identified and were usually of similar value in black and non-black subjects. These may be used to correct effects of dietary measurement errors in the AHS-2 cohort, and in some cases they also provide evidence supporting the validity of the dietary data.

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.

Simultaneous pharmacokinetic modeling of alkylresorcinols and their main metabolites indicates dual absorption mechanisms and enterohepatic elimination in humans

BACKGROUND

Alkylresorcinols have proven to be useful biomarkers of whole-grain wheat and rye intake in many nutritional studies. To improve their utility, more knowledge regarding the fate of alkylresorcinols and their metabolites after consumption is needed.

OBJECTIVE

The objective of this study was to develop a combined pharmacokinetic model for plasma concentrations of alkylresorcinols and their 2 major metabolites, 3,5-dihydroxybenzoic acid (DHBA) and 3-(3,5-dihydroxyphenyl)-propanoic acid (DHPPA).

METHODS

The model was established by using plasma samples collected from 3 women and 2 men after a single dose (120 g) of rye bran and validated against fasting plasma concentrations from 8 women and 7 men with controlled rye bran intake (23, 45, or 90 g/d). Alkylresorcinols in the lymph and plasma of a pig fed a single alkylresorcinol dose (1.3 mmol) were quantified to assess absorption. Human ileostomal effluent and pig bile after high and low alkylresorcinol doses were analyzed to evaluate biliary alkylresorcinol metabolite excretion.

RESULTS

The model contained 2 absorption compartments: 1 that transferred alkylresorcinols directly to the systematic circulation and 1 in which a proportion of absorbed alkylresorcinols was metabolized before reaching the systemic circulation. Plasma concentrations of alkylresorcinols and their metabolites depended on absorption and formation, respectively, and the mean ± SEM terminal elimination half-life of alkylresorcinols (1.9 ± 0.59 h), DHPPA (1.5 ± 0.26 h), and DHBA (1.3 ± 0.22 h) did not differ. The model accurately predicted alkylresorcinol and DHBA concentrations after repeated alkylresorcinol intake but DHPPA concentration was overpredicted, possibly because of poorly modeled enterohepatic circulation. During the 8 h following administration, <2% of the alkylresorcinol dose was recovered in the lymph. DHPPA was identified in both human ileostomal effluent and pig bile, indicating availability of DHPPA for absorption and enterohepatic circulation.

CONCLUSION

Intact alkylresorcinols have advantages over DHBA and DHPPA as plasma biomarkers for whole-grain wheat and rye intake because of lower susceptibility to factors other than alkylresorcinol intake.

Measuring exposure to the polyphenol metabolome in observational epidemiologic studies: current tools and applications and their limits

Much experimental evidence supports a protective role of dietary polyphenols against chronic diseases such as cardiovascular diseases, diabetes, and cancer. However, results from observational epidemiologic studies are still limited and are often inconsistent. This is largely explained by the difficulties encountered in the estimation of exposure to the polyphenol metabolome, which is composed of ~500 polyphenols distributed across a wide variety of foods and characterized by diverse biological properties. Exposure to the polyphenol metabolome in epidemiologic studies can be assessed by the use of detailed dietary questionnaires or the measurement of biomarkers of polyphenol intake. The questionnaire approach has been greatly facilitated by the use of new databases on polyphenol composition but is limited by bias as a result of self-reporting. The use of polyphenol biomarkers holds much promise for objective estimation of polyphenol exposure in future metabolome-wide association studies. These approaches are reviewed and their advantages and limitations discussed by using examples of epidemiologic studies on polyphenols and cancer. The current improvement in these techniques, along with greater emphasis on the intake of individual polyphenols rather than polyphenols considered collectively, will help unravel the role of these major food bioactive constituents in disease prevention.

The food metabolome: a window over dietary exposure

The food metabolome is defined as the part of the human metabolome directly derived from the digestion and biotransformation of foods and their constituents. With >25,000 compounds known in various foods, the food metabolome is extremely complex, with a composition varying widely according to the diet. By its very nature it represents a considerable and still largely unexploited source of novel dietary biomarkers that could be used to measure dietary exposures with a high level of detail and precision. Most dietary biomarkers currently have been identified on the basis of our knowledge of food compositions by using hypothesis-driven approaches. However, the rapid development of metabolomics resulting from the development of highly sensitive modern analytic instruments, the availability of metabolite databases, and progress in (bio)informatics has made agnostic approaches more attractive as shown by the recent identification of novel biomarkers of intakes for fruit, vegetables, beverages, meats, or complex diets. Moreover, examples also show how the scrutiny of the food metabolome can lead to the discovery of bioactive molecules and dietary factors associated with diseases. However, researchers still face hurdles, which slow progress and need to be resolved to bring this emerging field of research to maturity. These limits were discussed during the First International Workshop on the Food Metabolome held in Glasgow. Key recommendations made during the workshop included more coordination of efforts; development of new databases, software tools, and chemical libraries for the food metabolome; and shared repositories of metabolomic data. Once achieved, major progress can be expected toward a better understanding of the complex interactions between diet and human health.

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, 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 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.

Intake of whole-grain and fiber-rich rye bread versus refined wheat bread does not differentiate intestinal microbiota composition in Finnish adults with metabolic syndrome

Whole-grain (WG) foods rich in indigestible carbohydrates are thought to modulate the composition of the intestinal microbiota. We investigated in a randomized, parallel, 2-arm 12-wk intervention whether consumption of WG and fiber-rich rye breads compared with refined wheat breads affected the microbiota composition in Finnish individuals aged 60 ± 6 y with metabolic syndrome. Fecal samples from 51 participants (25 males, 26 females) before and after the intervention were processed for the microbiota analysis using a phylogenetic microarray and quantitative polymerase chain reactions targeting the 16S rRNA gene. The intake of whole grains calculated from food records was higher in the group consuming rye breads (75 g) than in that consuming refined wheat breads (4 g; P < 0.001), confirmed by fasting plasma alkylrecorsinol concentrations, a biomarker of whole grain intake. The intestinal microbiota composition did not significantly differ between the groups after the intervention. However, we detected a 37% decrease of Bacteroidetes (P < 0.05) in parallel to a 53% decrease in the alkylrecorsinol concentration (P < 0.001) in the group consuming refined wheat breads. In this group, the abundance of bacteria related to Bacteroides vulgatus, B. plebeius, and Prevotella tannerae decreased, whereas that of bacteria related to Collinsella and members of the Clostridium clusters IV and XI increased. In a multivariate regression analysis, the abundance of Bacteroides spp. was best explained by different fat compounds among dietary variables, whereas the main sugar-converting butyrate-producers were mostly associated with the intake of whole- and refined-grain bread and fiber. Our results indicate that the quality of grains has a minor effect on the intestinal microbiota composition in participants with metabolic syndrome and suggest that the dietary influence on the microbiota involves other dietary components such as fat.

LC-QTOF/MS metabolomic profiles in human plasma after a 5-week high dietary fiber intake

The objective was to investigate the alterations of plasma metabolome profiles to identify exposure and effect markers of dietary fiber intake. Subjects (n = 25) aged 58.6 (1.1) years (mean and SD) with a body mass index of 26.6 (0.5) kg/m(2) were given a high fiber (HF) and a low fiber (LF) diet, in a 5-week randomized controlled crossover intervention. The HF diet consisted of oat bran, rye bran, and sugar beet fiber incorporated into test food products, whereas the LF diet was made of equivalent food products to the HF diet, but without adding fibers. Blood plasma samples were collected at the start and end of each intervention period and analyzed by LC-QTOF/MS. In total, 6 features in positive mode and 14 features in negative mode were significantly different between the HF and the LF diet (p < 0.01, q < 0.05). Two markers, 2,6-dihydroxybenzoic acid and 2-aminophenol sulfate, were increased after HF diet, along with a tentatively identified saponin derived from oat avenacosides. The untargeted metabolomics approach enabled the identification of two new markers of dietary fiber intake in human plasma. Further studies will be needed to verify if these markers could serve as compliance markers of fiber intake.

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.

Dietary biomarkers: advances, limitations and future directions

The subjective nature of self-reported dietary intake assessment methods presents numerous challenges to obtaining accurate dietary intake and nutritional status. This limitation can be overcome by the use of dietary biomarkers, which are able to objectively assess dietary consumption (or exposure) without the bias of self-reported dietary intake errors. The need for dietary biomarkers was addressed by the Institute of Medicine, who recognized the lack of nutritional biomarkers as a knowledge gap requiring future research. The purpose of this article is to review existing literature on currently available dietary biomarkers, including novel biomarkers of specific foods and dietary components, and assess the validity, reliability and sensitivity of the markers. This review revealed several biomarkers in need of additional validation research; research is also needed to produce sensitive, specific, cost-effective and noninvasive dietary biomarkers. The emerging field of metabolomics may help to advance the development of food/nutrient biomarkers, yet advances in food metabolome databases are needed. The availability of biomarkers that estimate intake of specific foods and dietary components could greatly enhance nutritional research targeting compliance to national recommendations as well as direct associations with disease outcomes. More research is necessary to refine existing biomarkers by accounting for confounding factors, to establish new indicators of specific food intake, and to develop techniques that are cost-effective, noninvasive, rapid and accurate measures of nutritional status.

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.