The Carbon Isotope Ratios of Serum Amino Acids in Combination with Participant Characteristics can be Used to Estimate Added Sugar Intake in a Controlled Feeding Study of US Postmenopausal Women

Carbon stable isotope values in hair are associated with added sugar intake in adults but not young children: a cross-sectional study

BACKGROUND

Carbon (δ13C) and nitrogen (δ15N) stable isotope ratios in tissues are proposed biomarkers for dietary intake, with δ13C values reflecting added sugar intake derived from corn and sugarcane, and δ15N values reflecting animal protein intake. Research in young children is limited.

OBJECTIVE

We examined associations between hair δ13C and δ15N values and dietary intake among children and also their mothers, to confirm associations found in other adults.

METHODS

Hair samples and 24-h dietary recalls were collected from children (aged 5.6 ± 0.2 y; n = 138) and adults (34.1 ± 0.7 y; n = 114) in a cross-sectional study in Philadelphia. Hair δ13C and δ15N values were determined by continuous-flow isotope ratio mass spectrometry. Intake assessments focused on foods with high δ13C values [e.g. sugar-sweetened beverages (SSB)], high δ15N values (e.g. meat), or both (e.g. cow's milk). Three analytical approaches-single- (δ13C), dual- (δ13C, δ15N) isotope regression models and, uniquely, k-means cluster analysis-were used to assess associations.

RESULTS

Among adults, regression models revealed positive associations of δ13C values with added sugar [β (95% confidence interval): single, 0.17 (-0.01, 0.36); dual, 0.31 (0.10, 0.53)] and SSB [single, 0.30 (0.12, 0.48); dual, 0.31 (0.09, 0.53)] intakes, confirming prior findings. Adults in the high δ13C-δ15N cluster drank more SSB than the low cluster (213 ± 23 compared with 109 ± 20 kcal/d, P = 0.03). Among children, no such associations were found. However, children in the high δ13C-δ15N cluster consumed more cow's milk (81 ± 9 compared with 31 ± 7 kcal/d, P = 0.009) and animal proteins (408 ± 33 compared with 272 ± 36 kcal/d, P = 0.04). Their cow's milk intake is significantly associated with δ13C and δ15N values.

CONCLUSIONS

Age-related dietary patterns, particularly higher cow's milk consumption in children, may mask δ13C-added sugar associations, highlighting the importance of accounting for age and dietary complexity in biomarker research. This study was registered at: Snacks, Smiles and Taste Preferences as registration number NCT03631992. Website: https://clinicaltrials.gov/study/NCT03631992; Added Sugar Intake, Sweet Taste Phenotypes and Biomarkers (SWBIO), NCT05047588. Website: https://clinicaltrials.gov/ct2/show/NCT05047588.

Associations of Food Group Intakes with Serum Carbon Isotope Ratio Values in Youth: Results from 2 Prospective Pediatric Cohort Studies

BACKGROUND

The carbon isotope ratio (CIR) is a candidate biomarker for sugar-sweetened beverage (SSB) intake in the United States. However, research specific to youth, who differ in their physiology and dietary patterns compared with adults, is lacking.

OBJECTIVES

We evaluated longitudinal associations of SSB intakes across childhood/adolescence with serum CIR. We also explored the relationship between other dietary intakes and serum CIR.

METHODS

Data were from participants in two longitudinal, pediatric cohorts in Colorado: Exploring Perinatal Outcomes among CHildren (EPOCH) study (visits at median 10 and 16 y, n = 150) and Healthy Start Study (visits at median 5 and 9 y, n = 166). Serum CIR was measured using isotope ratio mass spectrometry. Diet was assessed by food-frequency questionnaires (EPOCH) or 24-h diet recalls (Healthy Start). We assessed associations of longitudinal dietary intakes (log2-transformed, standardized) with serum CIR using linear mixed models adjusted for age, sex, and energy intake, and associations of change values between visits using linear regression models.

RESULTS

In linear mixed models, higher SSB intake across visits was associated with higher serum CIR in both cohorts [β (95% confidence interval (CI)): 0.11 (0.06, 0.15) in EPOCH and 0.14 (0.07, 0.21) in Healthy Start]. Higher meat intake and a higher dietary animal protein ratio were also positively associated with serum CIR in both cohorts [β (95% CI): 0.08 (0.05, 0.12) and 0.18 (0.13, 0.23) in EPOCH; 0.08 (0.01, 0.16) and 0.28 (0.21, 0.35) in Healthy Start]. In change analyses, there were positive associations for changes in the dietary animal protein ratio between visits with changes in serum CIR in both cohorts, but not for changes in SSB intake.

CONCLUSIONS

Our findings support serum CIR as a potential biomarker of SSB intake in youth cross-sectionally; however, there was not a strong link between change values over longer-term follow-up. Meat/animal protein intake was also consistently and, at times, more strongly associated with serum CIR.

The carbon isotope ratio of breath is elevated by short-term and long-term added sugar and animal protein intake in a controlled feeding study

BACKGROUND

The breath carbon isotope ratio (CIR) was recently identified as a noninvasive candidate biomarker of short-term added sugars (AS) intake.

OBJECTIVES

This study aimed to better understand the potential of the breath CIR as a dietary biomarker. We evaluated the effects of short-term and long-term intakes of AS, animal protein (AP), and related variables on breath CIR, in the context of typical dietary intake patterns.

METHODS

We conducted a 15-d controlled feeding study of 100 adults (age 18-70 y, 55% females) in Phoenix, AZ. Participants were provided individualized diets that approximated habitual food intakes and recorded the timing of food consumption. Three breath samples (fasting, midday, and evening) were collected on each of 3 nonconsecutive study days. We modeled the effects of dietary intake in each of 8 h preceding collection of the breath sample on breath CIR with a linear mixed model, which also included 15-d mean intakes, sex, age, and BMI.

RESULTS

Median (IQR) intakes of AS and AP in our study were 65 (38) and 67 (33) g/d, respectively. Midday and evening breath CIRs correlated strongly with each other (0.80) and with fasting breath CIR (0.77 and 0.68, respectively). In our linear mixed models, breath CIR increased by AS consumed 1-4 h before sample collection, AP consumed 3-6 h before sample collection, and 15-d intakes of AS and AP, all with similar effect sizes. The breath CIR was also inversely associated with 15-d intakes of intrinsic sugars and plant protein; thus, associations with 15-d intakes were particularly strong when expressed proportionally as the AS ratio (added sugars/total sugars) and AP ratio (animal protein/total protein).

CONCLUSIONS

The breath CIR is a promising measure of long-term intakes of AS and AP, especially as proportional intakes. Approaches to increase specificity would benefit the further development of this biomarker.

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.

The Carbon Isotope Ratio as an Objective Biomarker of Added Sugar Intake: A Scoping Review of Current Evidence in Human Nutrition

Objective biomarkers of dietary intake are needed to advance nutrition research. The carbon isotope ratio (C13/C12; CIR) holds promise as an objective biomarker of added sugar (AS) and sugar-sweetened beverage (SSB) intake. This systematic scoping review presents the current evidence on CIRs from human studies. Search results (through April 12, 2024) yielded 6297 studies and 24 final articles. Studies were observational (n = 12), controlled feeding (n = 10), or dietary interventions (n = 2). CIRs were sampled from blood (n = 23), hair (n = 5), breath (n = 2), and/or adipose tissue (n = 1). Most (n = 17) conducted whole tissue (that is, bulk) analysis, 8 used compound specific isotope analysis (CSIA), and/or 2 studies used methods appropriate for analyzing breath. Studies were conducted in 3 concentrated geographic regions of the United States (n = 7 Virginia; n = 5 Arizona; n = 4 Alaska), with only 2 studies conducted in other countries. Studies that used CSIA to examine the CIR from the amino acid alanine (CIR-Ala; n = 4) and CIR analyzed from breath (n = 2) provided the most robust evidence for CIR as an objective biomarker of AS and SSBs (R2 range 0.36-0.91). Studies using bulk analysis of hair or blood showed positive, but modest and more variable associations with AS and SSBs (R2 range 0.05-0.48). Few studies showed no association, particularly in non-United States populations and those with low AS and SSB intakes. Two studies provided evidence for CIR to detect changes in SSB intake in response to dietary interventions. Overall, the most compelling evidence supports CIR-Ala as an objective indicator of AS intake and breath CIR as an indicator of short-term AS intake. Considering how to adjust for underlying dietary patterns remains an important area of future work and emerging methods using breath and CSIA warrant additional investigation. More evidence is needed to refine the utility and specificity of CIRs to measure AS and SSB intake.

Carbon Isotope Ratios of Plasma and RBC Fatty Acids Identify Meat Consumers in a 12-Week Inpatient Feeding Study of 32 Men

BACKGROUND

Molecular stable isotope ratios are a novel type of dietary biomarker with high sensitivity and specificity for certain foods. Among these, fatty acid carbon isotope ratios (CIRs) have strong potential but have not been investigated as dietary biomarkers.

OBJECTIVES

We evaluated whether fatty acid CIRs and mass proportions were associated with meat, fish, and sugar-sweetened beverage (SSB) intake.

METHODS

Thirty-two men [aged 46.2 ± 10.5 y; BMI (kg/m2): 27.2 ± 4.0] underwent a 12-wk inpatient dietary intervention at the National Institute of Diabetes and Digestive and Kidney Diseases in Phoenix, Arizona. Men were randomly assigned to 1 of 8 dietary treatments varying the presence/absence of dietary meat, fish, and SSBs in all combinations. Fatty acid CIRs and mass proportions were measured in fasting blood samples and adipose tissue biopsies that were collected pre- and postintervention. Dietary effects were analyzed using multivariable regression and receiver operating characteristic AUCs were calculated using logistic regression.

RESULTS

CIRs of the several abundant SFAs, MUFAs and arachidonic acid (20:4n-6) in plasma were strongly associated with meat, as were a subset of these fatty acids in RBCs. Effect sizes in plasma ranged from 1.01‰ to 1.93‰ and were similar but attenuated in RBCs. Mass proportions of those fatty acids were not associated with diet. CIRs of plasma dihomo-γ-linolenic acid (20:3n-6) and adipose palmitic acid (16:0) were weakly associated with SSBs. Mass proportions of plasma odd-chain fatty acids were associated with meat, and mass proportions of plasma EPA and DHA (20:5n-3 and 22:6n-3) were associated with fish.

CONCLUSIONS

CIRs of plasma and RBC fatty acids show promise as sensitive and specific measures of dietary meat. These provide different information from that provided by fatty acid mass proportions, and are informative where mass proportion is not. This trial is registered at www.clinicaltrials.gov as NCT01237093.

Stable isotope ratios of nitrogen and carbon as biomarkers of a vegan diet

PURPOSE

Dietary biomarkers can potentially overcome the limitations of self-reported dietary data. While in ecology and archaeology, stable isotope ratios of carbon and nitrogen are widely used as biomarkers, this is not the case in nutrition research. Since the abundance of the 13C and the 15N isotope differ in food sources from plant and animal origin, stable isotope ratios of carbon and nitrogen (δ13C and δ15N) may differ in human biological material. Here, we investigated the stable isotope ratios of nitrogen and carbon in serum and urine from vegans and omnivores.

METHOD

Measurement of δ15N and δ13C in serum and 24 h urine was performed by Elemental Analyzer-Isotope Ratio Mass Spectrometer in the cross-sectional study "Risks and Benefits of a Vegan Diet". The study included 36 vegans and 36 omnivores with a median age of 37.5 years (matched for age and sex), who adhered to their diet for at least 1 year.

RESULTS

Both δ15N and δ13C were significantly lower in both the serum and 24 h urine of vegans compared to omnivores. δ15N either in serum or urine had 100% specificity and sensitivity to discriminate between vegans and omnivores. Specificity of δ13C was also > 90%, while sensitivity was 93% in serum and 77% in urine.

CONCLUSION

δ15N both in serum and urine was able to accurately identify vegans and thus appears to be a promising marker for dietary habits.

Evaluating a Model of Added Sugar Intake Based on Amino Acid Carbon Isotope Ratios in a Controlled Feeding Study of U.S. Adults

Previous studies suggest that amino acid carbon stable isotope ratios (CIRAAs) may serve as biomarkers of added sugar (AS) intake, but this has not been tested in a demographically diverse population. We conducted a 15-day feeding study of U.S. adults, recruited across sex, age, and BMI groups. Participants consumed personalized diets that resembled habitual intake, assessed using two consecutive 7-day food records. We measured serum (n = 99) CIRAAs collected at the end of the feeding period and determined correlations with diet. We used forward selection to model AS intake using participant characteristics and 15 CIRAAs. This model was internally validated using bootstrap optimism correction. Median (25th, 75th percentile) AS intake was 65.2 g/day (44.7, 81.4) and 9.5% (7.2%, 12.4%) of energy. The CIR of alanine had the highest, although modest, correlation with AS intake (r = 0.32, p = 0.001). Serum CIRAAs were more highly correlated with animal food intakes, especially the ratio of animal to total protein. The AS model included sex, body weight and 6 CIRAAs. This model had modest explanatory power (multiple R2 = 0.38), and the optimism-corrected R2 was lower (R2 = 0.15). Further investigations in populations with wider ranges of AS intake are warranted.

Sugars measured enzymatically in a fasting overnight urine sample are not sensitive biomarkers of dietary added sugar intake in postmenopausal women

BACKGROUND

Restricting dietary sugar is a leading recommendation, but limited biomarkers assessing intake exist. Although 24-h urinary sucrose (U-Suc) and urinary fructose (U-Fruc) excretion has been used with mixed success, collection is burdensome.

AIM

This study aimed to test the sensitivity of an enzymatic assay of U-Suc and U-Fruc to detect changing added sugar intake using low-burden overnight urine samples in 30 postmenopausal women.

METHODS

Women consumed usual dietary intake during day 1 and usual intake plus a sugar sweetened beverage during day 2. Weighed, photographed food records assessed intake. Enzymatic assay measured U-Suc and U-Fruc from fasting overnight samples; liquid chromatography mass spectrometry (LC-MS) validated U-Suc findings.

RESULTS

Dietary added sugars increased significantly during day 2 (p < 0.001), but urinary sugars were not significantly increased. Enzymatic assay detected urinary sugars in 75% (U-Suc) and 35% (U-Fruc) of samples. Dietary sucrose was not associated with U-Suc, however dietary fructose was significantly associated with U-Fruc [β = 0.031; p < 0.05] among women with detectable urinary sugars. Participants with detectable U-Fruc consumed more energy from added sugars [12.6% kcal day 1; 21.5% kcal day 2] than participants with undetectable U-Fruc [9.3% kcal day 1; 17.4% kcal day 2], p < 0.05. Using LC-MS, U-Suc predicted sucrose and added sugar intake [β = 0.017, β = 0.013 respectively; both p < 0.05].

CONCLUSIONS

Urinary sugars measured enzymatically from overnight urine samples were not sensitive biomarkers of changing added sugar intake in postmenopausal women. However, urinary fructose measured by enzymatic assay or LC-MS may differentiate low versus high added sugar consumers.

OUP accepted manuscript

Stable isotope analysis of teeth and bones is regularly applied by archeologists and paleoanthropologists seeking to reconstruct diets, ecologies, and environments of past hominin populations. Moving beyond the now prevalent study of stable isotope ratios from bulk materials, researchers are increasingly turning to stable isotope ratios of individual amino acids to obtain more detailed and robust insights into trophic level and resource use. In the present article, we provide a guide on how to best use amino acid stable isotope ratios to determine hominin dietary behaviors and ecologies, past and present. We highlight existing uncertainties of interpretation and the methodological developments required to ensure good practice. In doing so, we hope to make this promising approach more broadly accessible to researchers at a variety of career stages and from a variety of methodological and academic backgrounds who seek to delve into new depths in the study of dietary composition.

A Systematic Review of Metabolomic Biomarkers for the Intake of Sugar-Sweetened and Low-Calorie Sweetened Beverages

Intake of added sugars (AS) is challenging to assess compared with total dietary sugar because of the lack of reliable assessment methods. The reliance on self-reported dietary data in observational studies is often cited as biased, with evidence of AS intake in relation to health outcomes rated as low to moderate quality. Sugar-sweetened beverages (SSBs) are a major source of AS. A regular and high intake of SSBs is associated with an overall poor diet, weight gain, and cardiometabolic risks. An elevated intake of low-calorie sweetened beverages (LCSBs), often regarded as healthier alternatives to SSBs, is also increasingly associated with increased risk for metabolic dysfunction. In this review, we systematically collate evidence and provide perspectives on the use of metabolomics for the discovery of candidate biomarkers associated with the intake of SSBs and LCSBs. We searched the Medline, Embase, Scopus, and Web of Science databases until the end of December 2020. Seventeen articles fulfilled our inclusion criteria. We evaluated specificity and validity of the identified biomarkers following Guidelines for Biomarker of Food Intake Reviews (BFIRev). We report that the ¹³C:¹²C carbon isotope ratio (δ¹³C), particularly, the δ¹³C of alanine is the most robust, sensitive, and specific biomarker of SSBs intake. Acesulfame-K, saccharin, sucralose, cyclamate, and steviol glucuronide showed moderate validity for predicting the short-term intake of LCSBs. More evidence is required to evaluate the validity of other panels of metabolites associated with the intake of SSBs.

UK Nutrition Research Partnership (NRP) workshop: Forum on advancing dietary intake assessment

The development of better and more robust measures of dietary intake in free living situations was identified as a priority for advancing nutrition research by the Office of Strategic Coordination for Health Research (OSCHR) Review of Nutrition and Human Health Research in 2017. The UK Nutrition Research Partnership (NRP) sponsored a workshop on Dietary Intake Assessment methodology alongside its series of ‘Hot Topic’ workshops designed to accelerate progress in nutrition research by bringing together people from a range of different disciplines. The workshop on Dietary Intake Assessment methodology took place via Zoom over two half‐days in January 2021 and included 50 scientists from a wide range of disciplines. The problems with current methods of dietary assessment and how emerging technologies might address them were set out in pre‐recorded presentations and explored in panel discussions. Participants then worked in breakout groups to discuss and prioritise the research questions that should be addressed to best further the field and lead to improvements in dietary assessment methodology. Five priority research questions were selected. Participants were asked to brainstorm potential approaches for addressing them and were then asked to focus on one approach and develop it further. At the end of these sessions, participants presented their project ideas to the rest of the workshop and these will be reported back to the Medical Research Council. It is hoped that potential collaborative projects arising from these discussions will be taken forward in response to future funding calls.

The carbon isotope ratios of nonessential amino acids identify sugar-sweetened beverage (SSB) consumers in a 12-wk inpatient feeding study of 32 men with varying SSB and meat exposures

BACKGROUND

The carbon isotope ratios (CIRs) of individual amino acids (AAs) may provide more sensitive and specific biomarkers of sugar-sweetened beverages (SSBs) than total tissue CIR. Because CIRs turn over slowly, long-term controlled-feeding studies are needed in their evaluation.

OBJECTIVE

We assessed the responses of plasma and RBC CIRAA's to SSB and meat intake in a 12-wk inpatient feeding study.

METHODS

Thirty-two men (aged 46.2 ± 10.5 y) completed the feeding study at the National Institute of Diabetes and Digestive and Kidney Diseases in Phoenix, Arizona. The effects of SSB, meat, and fish intake on plasma and RBC CIRAA's were evaluated in a balanced factorial design with each dietary variable either present or absent in a common weight-maintaining, macronutrient-balanced diet. Fasting blood samples were collected biweekly from baseline. Dietary effects on the postfeeding CIR of 5 nonessential AAs (CIRNEAA's) and 4 essential AAs (CIREAA's) were analyzed using multivariable regression.

RESULTS

In plasma, 4 of 5 CIRNEAA's increased with SSB intake. Of these, the CIRAla was the most sensitive (β = 2.81, SE = 0.38) to SSB intake and was not affected by meat or fish intake. In RBCs, all 5 CIRNEAA's increased with SSBs but had smaller effect sizes than in plasma. All plasma CIREAA's increased with meat intake (but not SSB or fish intake), and the CIRLeu was the most sensitive (β = 1.26, SE = 0.23). CIRs of leucine and valine also increased with meat intake in RBCs. Estimates of turnover suggest that CIRAA's in plasma, but not RBCs, were in equilibrium with the diets by the end of the study.

CONCLUSIONS

The results of this study in men support CIRNEAA's as potential biomarkers of SSB intake and suggest CIREAA's as potential biomarkers of meat intake in US diets. This trial was registered at clinicaltrials.gov/ct2/show/NCT01237093 as NCT01237093.